linux/fs/namespace.c
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   1/*
   2 *  linux/fs/namespace.c
   3 *
   4 * (C) Copyright Al Viro 2000, 2001
   5 *      Released under GPL v2.
   6 *
   7 * Based on code from fs/super.c, copyright Linus Torvalds and others.
   8 * Heavily rewritten.
   9 */
  10
  11#include <linux/syscalls.h>
  12#include <linux/export.h>
  13#include <linux/capability.h>
  14#include <linux/mnt_namespace.h>
  15#include <linux/user_namespace.h>
  16#include <linux/namei.h>
  17#include <linux/security.h>
  18#include <linux/idr.h>
  19#include <linux/acct.h>         /* acct_auto_close_mnt */
  20#include <linux/init.h>         /* init_rootfs */
  21#include <linux/fs_struct.h>    /* get_fs_root et.al. */
  22#include <linux/fsnotify.h>     /* fsnotify_vfsmount_delete */
  23#include <linux/uaccess.h>
  24#include <linux/proc_ns.h>
  25#include <linux/magic.h>
  26#include "pnode.h"
  27#include "internal.h"
  28
  29#define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
  30#define HASH_SIZE (1UL << HASH_SHIFT)
  31
  32static int event;
  33static DEFINE_IDA(mnt_id_ida);
  34static DEFINE_IDA(mnt_group_ida);
  35static DEFINE_SPINLOCK(mnt_id_lock);
  36static int mnt_id_start = 0;
  37static int mnt_group_start = 1;
  38
  39static struct list_head *mount_hashtable __read_mostly;
  40static struct list_head *mountpoint_hashtable __read_mostly;
  41static struct kmem_cache *mnt_cache __read_mostly;
  42static struct rw_semaphore namespace_sem;
  43
  44/* /sys/fs */
  45struct kobject *fs_kobj;
  46EXPORT_SYMBOL_GPL(fs_kobj);
  47
  48/*
  49 * vfsmount lock may be taken for read to prevent changes to the
  50 * vfsmount hash, ie. during mountpoint lookups or walking back
  51 * up the tree.
  52 *
  53 * It should be taken for write in all cases where the vfsmount
  54 * tree or hash is modified or when a vfsmount structure is modified.
  55 */
  56DEFINE_BRLOCK(vfsmount_lock);
  57
  58static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
  59{
  60        unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
  61        tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
  62        tmp = tmp + (tmp >> HASH_SHIFT);
  63        return tmp & (HASH_SIZE - 1);
  64}
  65
  66#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
  67
  68/*
  69 * allocation is serialized by namespace_sem, but we need the spinlock to
  70 * serialize with freeing.
  71 */
  72static int mnt_alloc_id(struct mount *mnt)
  73{
  74        int res;
  75
  76retry:
  77        ida_pre_get(&mnt_id_ida, GFP_KERNEL);
  78        spin_lock(&mnt_id_lock);
  79        res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
  80        if (!res)
  81                mnt_id_start = mnt->mnt_id + 1;
  82        spin_unlock(&mnt_id_lock);
  83        if (res == -EAGAIN)
  84                goto retry;
  85
  86        return res;
  87}
  88
  89static void mnt_free_id(struct mount *mnt)
  90{
  91        int id = mnt->mnt_id;
  92        spin_lock(&mnt_id_lock);
  93        ida_remove(&mnt_id_ida, id);
  94        if (mnt_id_start > id)
  95                mnt_id_start = id;
  96        spin_unlock(&mnt_id_lock);
  97}
  98
  99/*
 100 * Allocate a new peer group ID
 101 *
 102 * mnt_group_ida is protected by namespace_sem
 103 */
 104static int mnt_alloc_group_id(struct mount *mnt)
 105{
 106        int res;
 107
 108        if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
 109                return -ENOMEM;
 110
 111        res = ida_get_new_above(&mnt_group_ida,
 112                                mnt_group_start,
 113                                &mnt->mnt_group_id);
 114        if (!res)
 115                mnt_group_start = mnt->mnt_group_id + 1;
 116
 117        return res;
 118}
 119
 120/*
 121 * Release a peer group ID
 122 */
 123void mnt_release_group_id(struct mount *mnt)
 124{
 125        int id = mnt->mnt_group_id;
 126        ida_remove(&mnt_group_ida, id);
 127        if (mnt_group_start > id)
 128                mnt_group_start = id;
 129        mnt->mnt_group_id = 0;
 130}
 131
 132/*
 133 * vfsmount lock must be held for read
 134 */
 135static inline void mnt_add_count(struct mount *mnt, int n)
 136{
 137#ifdef CONFIG_SMP
 138        this_cpu_add(mnt->mnt_pcp->mnt_count, n);
 139#else
 140        preempt_disable();
 141        mnt->mnt_count += n;
 142        preempt_enable();
 143#endif
 144}
 145
 146/*
 147 * vfsmount lock must be held for write
 148 */
 149unsigned int mnt_get_count(struct mount *mnt)
 150{
 151#ifdef CONFIG_SMP
 152        unsigned int count = 0;
 153        int cpu;
 154
 155        for_each_possible_cpu(cpu) {
 156                count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
 157        }
 158
 159        return count;
 160#else
 161        return mnt->mnt_count;
 162#endif
 163}
 164
 165static struct mount *alloc_vfsmnt(const char *name)
 166{
 167        struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
 168        if (mnt) {
 169                int err;
 170
 171                err = mnt_alloc_id(mnt);
 172                if (err)
 173                        goto out_free_cache;
 174
 175                if (name) {
 176                        mnt->mnt_devname = kstrdup(name, GFP_KERNEL);
 177                        if (!mnt->mnt_devname)
 178                                goto out_free_id;
 179                }
 180
 181#ifdef CONFIG_SMP
 182                mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
 183                if (!mnt->mnt_pcp)
 184                        goto out_free_devname;
 185
 186                this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
 187#else
 188                mnt->mnt_count = 1;
 189                mnt->mnt_writers = 0;
 190#endif
 191
 192                INIT_LIST_HEAD(&mnt->mnt_hash);
 193                INIT_LIST_HEAD(&mnt->mnt_child);
 194                INIT_LIST_HEAD(&mnt->mnt_mounts);
 195                INIT_LIST_HEAD(&mnt->mnt_list);
 196                INIT_LIST_HEAD(&mnt->mnt_expire);
 197                INIT_LIST_HEAD(&mnt->mnt_share);
 198                INIT_LIST_HEAD(&mnt->mnt_slave_list);
 199                INIT_LIST_HEAD(&mnt->mnt_slave);
 200#ifdef CONFIG_FSNOTIFY
 201                INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
 202#endif
 203        }
 204        return mnt;
 205
 206#ifdef CONFIG_SMP
 207out_free_devname:
 208        kfree(mnt->mnt_devname);
 209#endif
 210out_free_id:
 211        mnt_free_id(mnt);
 212out_free_cache:
 213        kmem_cache_free(mnt_cache, mnt);
 214        return NULL;
 215}
 216
 217/*
 218 * Most r/o checks on a fs are for operations that take
 219 * discrete amounts of time, like a write() or unlink().
 220 * We must keep track of when those operations start
 221 * (for permission checks) and when they end, so that
 222 * we can determine when writes are able to occur to
 223 * a filesystem.
 224 */
 225/*
 226 * __mnt_is_readonly: check whether a mount is read-only
 227 * @mnt: the mount to check for its write status
 228 *
 229 * This shouldn't be used directly ouside of the VFS.
 230 * It does not guarantee that the filesystem will stay
 231 * r/w, just that it is right *now*.  This can not and
 232 * should not be used in place of IS_RDONLY(inode).
 233 * mnt_want/drop_write() will _keep_ the filesystem
 234 * r/w.
 235 */
 236int __mnt_is_readonly(struct vfsmount *mnt)
 237{
 238        if (mnt->mnt_flags & MNT_READONLY)
 239                return 1;
 240        if (mnt->mnt_sb->s_flags & MS_RDONLY)
 241                return 1;
 242        return 0;
 243}
 244EXPORT_SYMBOL_GPL(__mnt_is_readonly);
 245
 246static inline void mnt_inc_writers(struct mount *mnt)
 247{
 248#ifdef CONFIG_SMP
 249        this_cpu_inc(mnt->mnt_pcp->mnt_writers);
 250#else
 251        mnt->mnt_writers++;
 252#endif
 253}
 254
 255static inline void mnt_dec_writers(struct mount *mnt)
 256{
 257#ifdef CONFIG_SMP
 258        this_cpu_dec(mnt->mnt_pcp->mnt_writers);
 259#else
 260        mnt->mnt_writers--;
 261#endif
 262}
 263
 264static unsigned int mnt_get_writers(struct mount *mnt)
 265{
 266#ifdef CONFIG_SMP
 267        unsigned int count = 0;
 268        int cpu;
 269
 270        for_each_possible_cpu(cpu) {
 271                count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
 272        }
 273
 274        return count;
 275#else
 276        return mnt->mnt_writers;
 277#endif
 278}
 279
 280static int mnt_is_readonly(struct vfsmount *mnt)
 281{
 282        if (mnt->mnt_sb->s_readonly_remount)
 283                return 1;
 284        /* Order wrt setting s_flags/s_readonly_remount in do_remount() */
 285        smp_rmb();
 286        return __mnt_is_readonly(mnt);
 287}
 288
 289/*
 290 * Most r/o & frozen checks on a fs are for operations that take discrete
 291 * amounts of time, like a write() or unlink().  We must keep track of when
 292 * those operations start (for permission checks) and when they end, so that we
 293 * can determine when writes are able to occur to a filesystem.
 294 */
 295/**
 296 * __mnt_want_write - get write access to a mount without freeze protection
 297 * @m: the mount on which to take a write
 298 *
 299 * This tells the low-level filesystem that a write is about to be performed to
 300 * it, and makes sure that writes are allowed (mnt it read-write) before
 301 * returning success. This operation does not protect against filesystem being
 302 * frozen. When the write operation is finished, __mnt_drop_write() must be
 303 * called. This is effectively a refcount.
 304 */
 305int __mnt_want_write(struct vfsmount *m)
 306{
 307        struct mount *mnt = real_mount(m);
 308        int ret = 0;
 309
 310        preempt_disable();
 311        mnt_inc_writers(mnt);
 312        /*
 313         * The store to mnt_inc_writers must be visible before we pass
 314         * MNT_WRITE_HOLD loop below, so that the slowpath can see our
 315         * incremented count after it has set MNT_WRITE_HOLD.
 316         */
 317        smp_mb();
 318        while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
 319                cpu_relax();
 320        /*
 321         * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
 322         * be set to match its requirements. So we must not load that until
 323         * MNT_WRITE_HOLD is cleared.
 324         */
 325        smp_rmb();
 326        if (mnt_is_readonly(m)) {
 327                mnt_dec_writers(mnt);
 328                ret = -EROFS;
 329        }
 330        preempt_enable();
 331
 332        return ret;
 333}
 334
 335/**
 336 * mnt_want_write - get write access to a mount
 337 * @m: the mount on which to take a write
 338 *
 339 * This tells the low-level filesystem that a write is about to be performed to
 340 * it, and makes sure that writes are allowed (mount is read-write, filesystem
 341 * is not frozen) before returning success.  When the write operation is
 342 * finished, mnt_drop_write() must be called.  This is effectively a refcount.
 343 */
 344int mnt_want_write(struct vfsmount *m)
 345{
 346        int ret;
 347
 348        sb_start_write(m->mnt_sb);
 349        ret = __mnt_want_write(m);
 350        if (ret)
 351                sb_end_write(m->mnt_sb);
 352        return ret;
 353}
 354EXPORT_SYMBOL_GPL(mnt_want_write);
 355
 356/**
 357 * mnt_clone_write - get write access to a mount
 358 * @mnt: the mount on which to take a write
 359 *
 360 * This is effectively like mnt_want_write, except
 361 * it must only be used to take an extra write reference
 362 * on a mountpoint that we already know has a write reference
 363 * on it. This allows some optimisation.
 364 *
 365 * After finished, mnt_drop_write must be called as usual to
 366 * drop the reference.
 367 */
 368int mnt_clone_write(struct vfsmount *mnt)
 369{
 370        /* superblock may be r/o */
 371        if (__mnt_is_readonly(mnt))
 372                return -EROFS;
 373        preempt_disable();
 374        mnt_inc_writers(real_mount(mnt));
 375        preempt_enable();
 376        return 0;
 377}
 378EXPORT_SYMBOL_GPL(mnt_clone_write);
 379
 380/**
 381 * __mnt_want_write_file - get write access to a file's mount
 382 * @file: the file who's mount on which to take a write
 383 *
 384 * This is like __mnt_want_write, but it takes a file and can
 385 * do some optimisations if the file is open for write already
 386 */
 387int __mnt_want_write_file(struct file *file)
 388{
 389        struct inode *inode = file_inode(file);
 390
 391        if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
 392                return __mnt_want_write(file->f_path.mnt);
 393        else
 394                return mnt_clone_write(file->f_path.mnt);
 395}
 396
 397/**
 398 * mnt_want_write_file - get write access to a file's mount
 399 * @file: the file who's mount on which to take a write
 400 *
 401 * This is like mnt_want_write, but it takes a file and can
 402 * do some optimisations if the file is open for write already
 403 */
 404int mnt_want_write_file(struct file *file)
 405{
 406        int ret;
 407
 408        sb_start_write(file->f_path.mnt->mnt_sb);
 409        ret = __mnt_want_write_file(file);
 410        if (ret)
 411                sb_end_write(file->f_path.mnt->mnt_sb);
 412        return ret;
 413}
 414EXPORT_SYMBOL_GPL(mnt_want_write_file);
 415
 416/**
 417 * __mnt_drop_write - give up write access to a mount
 418 * @mnt: the mount on which to give up write access
 419 *
 420 * Tells the low-level filesystem that we are done
 421 * performing writes to it.  Must be matched with
 422 * __mnt_want_write() call above.
 423 */
 424void __mnt_drop_write(struct vfsmount *mnt)
 425{
 426        preempt_disable();
 427        mnt_dec_writers(real_mount(mnt));
 428        preempt_enable();
 429}
 430
 431/**
 432 * mnt_drop_write - give up write access to a mount
 433 * @mnt: the mount on which to give up write access
 434 *
 435 * Tells the low-level filesystem that we are done performing writes to it and
 436 * also allows filesystem to be frozen again.  Must be matched with
 437 * mnt_want_write() call above.
 438 */
 439void mnt_drop_write(struct vfsmount *mnt)
 440{
 441        __mnt_drop_write(mnt);
 442        sb_end_write(mnt->mnt_sb);
 443}
 444EXPORT_SYMBOL_GPL(mnt_drop_write);
 445
 446void __mnt_drop_write_file(struct file *file)
 447{
 448        __mnt_drop_write(file->f_path.mnt);
 449}
 450
 451void mnt_drop_write_file(struct file *file)
 452{
 453        mnt_drop_write(file->f_path.mnt);
 454}
 455EXPORT_SYMBOL(mnt_drop_write_file);
 456
 457static int mnt_make_readonly(struct mount *mnt)
 458{
 459        int ret = 0;
 460
 461        br_write_lock(&vfsmount_lock);
 462        mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
 463        /*
 464         * After storing MNT_WRITE_HOLD, we'll read the counters. This store
 465         * should be visible before we do.
 466         */
 467        smp_mb();
 468
 469        /*
 470         * With writers on hold, if this value is zero, then there are
 471         * definitely no active writers (although held writers may subsequently
 472         * increment the count, they'll have to wait, and decrement it after
 473         * seeing MNT_READONLY).
 474         *
 475         * It is OK to have counter incremented on one CPU and decremented on
 476         * another: the sum will add up correctly. The danger would be when we
 477         * sum up each counter, if we read a counter before it is incremented,
 478         * but then read another CPU's count which it has been subsequently
 479         * decremented from -- we would see more decrements than we should.
 480         * MNT_WRITE_HOLD protects against this scenario, because
 481         * mnt_want_write first increments count, then smp_mb, then spins on
 482         * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
 483         * we're counting up here.
 484         */
 485        if (mnt_get_writers(mnt) > 0)
 486                ret = -EBUSY;
 487        else
 488                mnt->mnt.mnt_flags |= MNT_READONLY;
 489        /*
 490         * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
 491         * that become unheld will see MNT_READONLY.
 492         */
 493        smp_wmb();
 494        mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
 495        br_write_unlock(&vfsmount_lock);
 496        return ret;
 497}
 498
 499static void __mnt_unmake_readonly(struct mount *mnt)
 500{
 501        br_write_lock(&vfsmount_lock);
 502        mnt->mnt.mnt_flags &= ~MNT_READONLY;
 503        br_write_unlock(&vfsmount_lock);
 504}
 505
 506int sb_prepare_remount_readonly(struct super_block *sb)
 507{
 508        struct mount *mnt;
 509        int err = 0;
 510
 511        /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
 512        if (atomic_long_read(&sb->s_remove_count))
 513                return -EBUSY;
 514
 515        br_write_lock(&vfsmount_lock);
 516        list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
 517                if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
 518                        mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
 519                        smp_mb();
 520                        if (mnt_get_writers(mnt) > 0) {
 521                                err = -EBUSY;
 522                                break;
 523                        }
 524                }
 525        }
 526        if (!err && atomic_long_read(&sb->s_remove_count))
 527                err = -EBUSY;
 528
 529        if (!err) {
 530                sb->s_readonly_remount = 1;
 531                smp_wmb();
 532        }
 533        list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
 534                if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
 535                        mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
 536        }
 537        br_write_unlock(&vfsmount_lock);
 538
 539        return err;
 540}
 541
 542static void free_vfsmnt(struct mount *mnt)
 543{
 544        kfree(mnt->mnt_devname);
 545        mnt_free_id(mnt);
 546#ifdef CONFIG_SMP
 547        free_percpu(mnt->mnt_pcp);
 548#endif
 549        kmem_cache_free(mnt_cache, mnt);
 550}
 551
 552/*
 553 * find the first or last mount at @dentry on vfsmount @mnt depending on
 554 * @dir. If @dir is set return the first mount else return the last mount.
 555 * vfsmount_lock must be held for read or write.
 556 */
 557struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
 558                              int dir)
 559{
 560        struct list_head *head = mount_hashtable + hash(mnt, dentry);
 561        struct list_head *tmp = head;
 562        struct mount *p, *found = NULL;
 563
 564        for (;;) {
 565                tmp = dir ? tmp->next : tmp->prev;
 566                p = NULL;
 567                if (tmp == head)
 568                        break;
 569                p = list_entry(tmp, struct mount, mnt_hash);
 570                if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry) {
 571                        found = p;
 572                        break;
 573                }
 574        }
 575        return found;
 576}
 577
 578/*
 579 * lookup_mnt - Return the first child mount mounted at path
 580 *
 581 * "First" means first mounted chronologically.  If you create the
 582 * following mounts:
 583 *
 584 * mount /dev/sda1 /mnt
 585 * mount /dev/sda2 /mnt
 586 * mount /dev/sda3 /mnt
 587 *
 588 * Then lookup_mnt() on the base /mnt dentry in the root mount will
 589 * return successively the root dentry and vfsmount of /dev/sda1, then
 590 * /dev/sda2, then /dev/sda3, then NULL.
 591 *
 592 * lookup_mnt takes a reference to the found vfsmount.
 593 */
 594struct vfsmount *lookup_mnt(struct path *path)
 595{
 596        struct mount *child_mnt;
 597
 598        br_read_lock(&vfsmount_lock);
 599        child_mnt = __lookup_mnt(path->mnt, path->dentry, 1);
 600        if (child_mnt) {
 601                mnt_add_count(child_mnt, 1);
 602                br_read_unlock(&vfsmount_lock);
 603                return &child_mnt->mnt;
 604        } else {
 605                br_read_unlock(&vfsmount_lock);
 606                return NULL;
 607        }
 608}
 609
 610static struct mountpoint *new_mountpoint(struct dentry *dentry)
 611{
 612        struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
 613        struct mountpoint *mp;
 614        int ret;
 615
 616        list_for_each_entry(mp, chain, m_hash) {
 617                if (mp->m_dentry == dentry) {
 618                        /* might be worth a WARN_ON() */
 619                        if (d_unlinked(dentry))
 620                                return ERR_PTR(-ENOENT);
 621                        mp->m_count++;
 622                        return mp;
 623                }
 624        }
 625
 626        mp = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
 627        if (!mp)
 628                return ERR_PTR(-ENOMEM);
 629
 630        ret = d_set_mounted(dentry);
 631        if (ret) {
 632                kfree(mp);
 633                return ERR_PTR(ret);
 634        }
 635
 636        mp->m_dentry = dentry;
 637        mp->m_count = 1;
 638        list_add(&mp->m_hash, chain);
 639        return mp;
 640}
 641
 642static void put_mountpoint(struct mountpoint *mp)
 643{
 644        if (!--mp->m_count) {
 645                struct dentry *dentry = mp->m_dentry;
 646                spin_lock(&dentry->d_lock);
 647                dentry->d_flags &= ~DCACHE_MOUNTED;
 648                spin_unlock(&dentry->d_lock);
 649                list_del(&mp->m_hash);
 650                kfree(mp);
 651        }
 652}
 653
 654static inline int check_mnt(struct mount *mnt)
 655{
 656        return mnt->mnt_ns == current->nsproxy->mnt_ns;
 657}
 658
 659/*
 660 * vfsmount lock must be held for write
 661 */
 662static void touch_mnt_namespace(struct mnt_namespace *ns)
 663{
 664        if (ns) {
 665                ns->event = ++event;
 666                wake_up_interruptible(&ns->poll);
 667        }
 668}
 669
 670/*
 671 * vfsmount lock must be held for write
 672 */
 673static void __touch_mnt_namespace(struct mnt_namespace *ns)
 674{
 675        if (ns && ns->event != event) {
 676                ns->event = event;
 677                wake_up_interruptible(&ns->poll);
 678        }
 679}
 680
 681/*
 682 * vfsmount lock must be held for write
 683 */
 684static void detach_mnt(struct mount *mnt, struct path *old_path)
 685{
 686        old_path->dentry = mnt->mnt_mountpoint;
 687        old_path->mnt = &mnt->mnt_parent->mnt;
 688        mnt->mnt_parent = mnt;
 689        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 690        list_del_init(&mnt->mnt_child);
 691        list_del_init(&mnt->mnt_hash);
 692        put_mountpoint(mnt->mnt_mp);
 693        mnt->mnt_mp = NULL;
 694}
 695
 696/*
 697 * vfsmount lock must be held for write
 698 */
 699void mnt_set_mountpoint(struct mount *mnt,
 700                        struct mountpoint *mp,
 701                        struct mount *child_mnt)
 702{
 703        mp->m_count++;
 704        mnt_add_count(mnt, 1);  /* essentially, that's mntget */
 705        child_mnt->mnt_mountpoint = dget(mp->m_dentry);
 706        child_mnt->mnt_parent = mnt;
 707        child_mnt->mnt_mp = mp;
 708}
 709
 710/*
 711 * vfsmount lock must be held for write
 712 */
 713static void attach_mnt(struct mount *mnt,
 714                        struct mount *parent,
 715                        struct mountpoint *mp)
 716{
 717        mnt_set_mountpoint(parent, mp, mnt);
 718        list_add_tail(&mnt->mnt_hash, mount_hashtable +
 719                        hash(&parent->mnt, mp->m_dentry));
 720        list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 721}
 722
 723/*
 724 * vfsmount lock must be held for write
 725 */
 726static void commit_tree(struct mount *mnt)
 727{
 728        struct mount *parent = mnt->mnt_parent;
 729        struct mount *m;
 730        LIST_HEAD(head);
 731        struct mnt_namespace *n = parent->mnt_ns;
 732
 733        BUG_ON(parent == mnt);
 734
 735        list_add_tail(&head, &mnt->mnt_list);
 736        list_for_each_entry(m, &head, mnt_list)
 737                m->mnt_ns = n;
 738
 739        list_splice(&head, n->list.prev);
 740
 741        list_add_tail(&mnt->mnt_hash, mount_hashtable +
 742                                hash(&parent->mnt, mnt->mnt_mountpoint));
 743        list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 744        touch_mnt_namespace(n);
 745}
 746
 747static struct mount *next_mnt(struct mount *p, struct mount *root)
 748{
 749        struct list_head *next = p->mnt_mounts.next;
 750        if (next == &p->mnt_mounts) {
 751                while (1) {
 752                        if (p == root)
 753                                return NULL;
 754                        next = p->mnt_child.next;
 755                        if (next != &p->mnt_parent->mnt_mounts)
 756                                break;
 757                        p = p->mnt_parent;
 758                }
 759        }
 760        return list_entry(next, struct mount, mnt_child);
 761}
 762
 763static struct mount *skip_mnt_tree(struct mount *p)
 764{
 765        struct list_head *prev = p->mnt_mounts.prev;
 766        while (prev != &p->mnt_mounts) {
 767                p = list_entry(prev, struct mount, mnt_child);
 768                prev = p->mnt_mounts.prev;
 769        }
 770        return p;
 771}
 772
 773struct vfsmount *
 774vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
 775{
 776        struct mount *mnt;
 777        struct dentry *root;
 778
 779        if (!type)
 780                return ERR_PTR(-ENODEV);
 781
 782        mnt = alloc_vfsmnt(name);
 783        if (!mnt)
 784                return ERR_PTR(-ENOMEM);
 785
 786        if (flags & MS_KERNMOUNT)
 787                mnt->mnt.mnt_flags = MNT_INTERNAL;
 788
 789        root = mount_fs(type, flags, name, data);
 790        if (IS_ERR(root)) {
 791                free_vfsmnt(mnt);
 792                return ERR_CAST(root);
 793        }
 794
 795        mnt->mnt.mnt_root = root;
 796        mnt->mnt.mnt_sb = root->d_sb;
 797        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 798        mnt->mnt_parent = mnt;
 799        br_write_lock(&vfsmount_lock);
 800        list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
 801        br_write_unlock(&vfsmount_lock);
 802        return &mnt->mnt;
 803}
 804EXPORT_SYMBOL_GPL(vfs_kern_mount);
 805
 806static struct mount *clone_mnt(struct mount *old, struct dentry *root,
 807                                        int flag)
 808{
 809        struct super_block *sb = old->mnt.mnt_sb;
 810        struct mount *mnt;
 811        int err;
 812
 813        mnt = alloc_vfsmnt(old->mnt_devname);
 814        if (!mnt)
 815                return ERR_PTR(-ENOMEM);
 816
 817        if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
 818                mnt->mnt_group_id = 0; /* not a peer of original */
 819        else
 820                mnt->mnt_group_id = old->mnt_group_id;
 821
 822        if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
 823                err = mnt_alloc_group_id(mnt);
 824                if (err)
 825                        goto out_free;
 826        }
 827
 828        mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~MNT_WRITE_HOLD;
 829        /* Don't allow unprivileged users to change mount flags */
 830        if ((flag & CL_UNPRIVILEGED) && (mnt->mnt.mnt_flags & MNT_READONLY))
 831                mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
 832
 833        /* Don't allow unprivileged users to reveal what is under a mount */
 834        if ((flag & CL_UNPRIVILEGED) && list_empty(&old->mnt_expire))
 835                mnt->mnt.mnt_flags |= MNT_LOCKED;
 836
 837        atomic_inc(&sb->s_active);
 838        mnt->mnt.mnt_sb = sb;
 839        mnt->mnt.mnt_root = dget(root);
 840        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 841        mnt->mnt_parent = mnt;
 842        br_write_lock(&vfsmount_lock);
 843        list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
 844        br_write_unlock(&vfsmount_lock);
 845
 846        if ((flag & CL_SLAVE) ||
 847            ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
 848                list_add(&mnt->mnt_slave, &old->mnt_slave_list);
 849                mnt->mnt_master = old;
 850                CLEAR_MNT_SHARED(mnt);
 851        } else if (!(flag & CL_PRIVATE)) {
 852                if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
 853                        list_add(&mnt->mnt_share, &old->mnt_share);
 854                if (IS_MNT_SLAVE(old))
 855                        list_add(&mnt->mnt_slave, &old->mnt_slave);
 856                mnt->mnt_master = old->mnt_master;
 857        }
 858        if (flag & CL_MAKE_SHARED)
 859                set_mnt_shared(mnt);
 860
 861        /* stick the duplicate mount on the same expiry list
 862         * as the original if that was on one */
 863        if (flag & CL_EXPIRE) {
 864                if (!list_empty(&old->mnt_expire))
 865                        list_add(&mnt->mnt_expire, &old->mnt_expire);
 866        }
 867
 868        return mnt;
 869
 870 out_free:
 871        free_vfsmnt(mnt);
 872        return ERR_PTR(err);
 873}
 874
 875static inline void mntfree(struct mount *mnt)
 876{
 877        struct vfsmount *m = &mnt->mnt;
 878        struct super_block *sb = m->mnt_sb;
 879
 880        /*
 881         * This probably indicates that somebody messed
 882         * up a mnt_want/drop_write() pair.  If this
 883         * happens, the filesystem was probably unable
 884         * to make r/w->r/o transitions.
 885         */
 886        /*
 887         * The locking used to deal with mnt_count decrement provides barriers,
 888         * so mnt_get_writers() below is safe.
 889         */
 890        WARN_ON(mnt_get_writers(mnt));
 891        fsnotify_vfsmount_delete(m);
 892        dput(m->mnt_root);
 893        free_vfsmnt(mnt);
 894        deactivate_super(sb);
 895}
 896
 897static void mntput_no_expire(struct mount *mnt)
 898{
 899put_again:
 900#ifdef CONFIG_SMP
 901        br_read_lock(&vfsmount_lock);
 902        if (likely(mnt->mnt_ns)) {
 903                /* shouldn't be the last one */
 904                mnt_add_count(mnt, -1);
 905                br_read_unlock(&vfsmount_lock);
 906                return;
 907        }
 908        br_read_unlock(&vfsmount_lock);
 909
 910        br_write_lock(&vfsmount_lock);
 911        mnt_add_count(mnt, -1);
 912        if (mnt_get_count(mnt)) {
 913                br_write_unlock(&vfsmount_lock);
 914                return;
 915        }
 916#else
 917        mnt_add_count(mnt, -1);
 918        if (likely(mnt_get_count(mnt)))
 919                return;
 920        br_write_lock(&vfsmount_lock);
 921#endif
 922        if (unlikely(mnt->mnt_pinned)) {
 923                mnt_add_count(mnt, mnt->mnt_pinned + 1);
 924                mnt->mnt_pinned = 0;
 925                br_write_unlock(&vfsmount_lock);
 926                acct_auto_close_mnt(&mnt->mnt);
 927                goto put_again;
 928        }
 929
 930        list_del(&mnt->mnt_instance);
 931        br_write_unlock(&vfsmount_lock);
 932        mntfree(mnt);
 933}
 934
 935void mntput(struct vfsmount *mnt)
 936{
 937        if (mnt) {
 938                struct mount *m = real_mount(mnt);
 939                /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
 940                if (unlikely(m->mnt_expiry_mark))
 941                        m->mnt_expiry_mark = 0;
 942                mntput_no_expire(m);
 943        }
 944}
 945EXPORT_SYMBOL(mntput);
 946
 947struct vfsmount *mntget(struct vfsmount *mnt)
 948{
 949        if (mnt)
 950                mnt_add_count(real_mount(mnt), 1);
 951        return mnt;
 952}
 953EXPORT_SYMBOL(mntget);
 954
 955void mnt_pin(struct vfsmount *mnt)
 956{
 957        br_write_lock(&vfsmount_lock);
 958        real_mount(mnt)->mnt_pinned++;
 959        br_write_unlock(&vfsmount_lock);
 960}
 961EXPORT_SYMBOL(mnt_pin);
 962
 963void mnt_unpin(struct vfsmount *m)
 964{
 965        struct mount *mnt = real_mount(m);
 966        br_write_lock(&vfsmount_lock);
 967        if (mnt->mnt_pinned) {
 968                mnt_add_count(mnt, 1);
 969                mnt->mnt_pinned--;
 970        }
 971        br_write_unlock(&vfsmount_lock);
 972}
 973EXPORT_SYMBOL(mnt_unpin);
 974
 975static inline void mangle(struct seq_file *m, const char *s)
 976{
 977        seq_escape(m, s, " \t\n\\");
 978}
 979
 980/*
 981 * Simple .show_options callback for filesystems which don't want to
 982 * implement more complex mount option showing.
 983 *
 984 * See also save_mount_options().
 985 */
 986int generic_show_options(struct seq_file *m, struct dentry *root)
 987{
 988        const char *options;
 989
 990        rcu_read_lock();
 991        options = rcu_dereference(root->d_sb->s_options);
 992
 993        if (options != NULL && options[0]) {
 994                seq_putc(m, ',');
 995                mangle(m, options);
 996        }
 997        rcu_read_unlock();
 998
 999        return 0;
1000}
1001EXPORT_SYMBOL(generic_show_options);
1002
1003/*
1004 * If filesystem uses generic_show_options(), this function should be
1005 * called from the fill_super() callback.
1006 *
1007 * The .remount_fs callback usually needs to be handled in a special
1008 * way, to make sure, that previous options are not overwritten if the
1009 * remount fails.
1010 *
1011 * Also note, that if the filesystem's .remount_fs function doesn't
1012 * reset all options to their default value, but changes only newly
1013 * given options, then the displayed options will not reflect reality
1014 * any more.
1015 */
1016void save_mount_options(struct super_block *sb, char *options)
1017{
1018        BUG_ON(sb->s_options);
1019        rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
1020}
1021EXPORT_SYMBOL(save_mount_options);
1022
1023void replace_mount_options(struct super_block *sb, char *options)
1024{
1025        char *old = sb->s_options;
1026        rcu_assign_pointer(sb->s_options, options);
1027        if (old) {
1028                synchronize_rcu();
1029                kfree(old);
1030        }
1031}
1032EXPORT_SYMBOL(replace_mount_options);
1033
1034#ifdef CONFIG_PROC_FS
1035/* iterator; we want it to have access to namespace_sem, thus here... */
1036static void *m_start(struct seq_file *m, loff_t *pos)
1037{
1038        struct proc_mounts *p = proc_mounts(m);
1039
1040        down_read(&namespace_sem);
1041        return seq_list_start(&p->ns->list, *pos);
1042}
1043
1044static void *m_next(struct seq_file *m, void *v, loff_t *pos)
1045{
1046        struct proc_mounts *p = proc_mounts(m);
1047
1048        return seq_list_next(v, &p->ns->list, pos);
1049}
1050
1051static void m_stop(struct seq_file *m, void *v)
1052{
1053        up_read(&namespace_sem);
1054}
1055
1056static int m_show(struct seq_file *m, void *v)
1057{
1058        struct proc_mounts *p = proc_mounts(m);
1059        struct mount *r = list_entry(v, struct mount, mnt_list);
1060        return p->show(m, &r->mnt);
1061}
1062
1063const struct seq_operations mounts_op = {
1064        .start  = m_start,
1065        .next   = m_next,
1066        .stop   = m_stop,
1067        .show   = m_show,
1068};
1069#endif  /* CONFIG_PROC_FS */
1070
1071/**
1072 * may_umount_tree - check if a mount tree is busy
1073 * @mnt: root of mount tree
1074 *
1075 * This is called to check if a tree of mounts has any
1076 * open files, pwds, chroots or sub mounts that are
1077 * busy.
1078 */
1079int may_umount_tree(struct vfsmount *m)
1080{
1081        struct mount *mnt = real_mount(m);
1082        int actual_refs = 0;
1083        int minimum_refs = 0;
1084        struct mount *p;
1085        BUG_ON(!m);
1086
1087        /* write lock needed for mnt_get_count */
1088        br_write_lock(&vfsmount_lock);
1089        for (p = mnt; p; p = next_mnt(p, mnt)) {
1090                actual_refs += mnt_get_count(p);
1091                minimum_refs += 2;
1092        }
1093        br_write_unlock(&vfsmount_lock);
1094
1095        if (actual_refs > minimum_refs)
1096                return 0;
1097
1098        return 1;
1099}
1100
1101EXPORT_SYMBOL(may_umount_tree);
1102
1103/**
1104 * may_umount - check if a mount point is busy
1105 * @mnt: root of mount
1106 *
1107 * This is called to check if a mount point has any
1108 * open files, pwds, chroots or sub mounts. If the
1109 * mount has sub mounts this will return busy
1110 * regardless of whether the sub mounts are busy.
1111 *
1112 * Doesn't take quota and stuff into account. IOW, in some cases it will
1113 * give false negatives. The main reason why it's here is that we need
1114 * a non-destructive way to look for easily umountable filesystems.
1115 */
1116int may_umount(struct vfsmount *mnt)
1117{
1118        int ret = 1;
1119        down_read(&namespace_sem);
1120        br_write_lock(&vfsmount_lock);
1121        if (propagate_mount_busy(real_mount(mnt), 2))
1122                ret = 0;
1123        br_write_unlock(&vfsmount_lock);
1124        up_read(&namespace_sem);
1125        return ret;
1126}
1127
1128EXPORT_SYMBOL(may_umount);
1129
1130static LIST_HEAD(unmounted);    /* protected by namespace_sem */
1131
1132static void namespace_unlock(void)
1133{
1134        struct mount *mnt;
1135        LIST_HEAD(head);
1136
1137        if (likely(list_empty(&unmounted))) {
1138                up_write(&namespace_sem);
1139                return;
1140        }
1141
1142        list_splice_init(&unmounted, &head);
1143        up_write(&namespace_sem);
1144
1145        while (!list_empty(&head)) {
1146                mnt = list_first_entry(&head, struct mount, mnt_hash);
1147                list_del_init(&mnt->mnt_hash);
1148                if (mnt_has_parent(mnt)) {
1149                        struct dentry *dentry;
1150                        struct mount *m;
1151
1152                        br_write_lock(&vfsmount_lock);
1153                        dentry = mnt->mnt_mountpoint;
1154                        m = mnt->mnt_parent;
1155                        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
1156                        mnt->mnt_parent = mnt;
1157                        m->mnt_ghosts--;
1158                        br_write_unlock(&vfsmount_lock);
1159                        dput(dentry);
1160                        mntput(&m->mnt);
1161                }
1162                mntput(&mnt->mnt);
1163        }
1164}
1165
1166static inline void namespace_lock(void)
1167{
1168        down_write(&namespace_sem);
1169}
1170
1171/*
1172 * vfsmount lock must be held for write
1173 * namespace_sem must be held for write
1174 */
1175void umount_tree(struct mount *mnt, int propagate)
1176{
1177        LIST_HEAD(tmp_list);
1178        struct mount *p;
1179
1180        for (p = mnt; p; p = next_mnt(p, mnt))
1181                list_move(&p->mnt_hash, &tmp_list);
1182
1183        if (propagate)
1184                propagate_umount(&tmp_list);
1185
1186        list_for_each_entry(p, &tmp_list, mnt_hash) {
1187                list_del_init(&p->mnt_expire);
1188                list_del_init(&p->mnt_list);
1189                __touch_mnt_namespace(p->mnt_ns);
1190                p->mnt_ns = NULL;
1191                list_del_init(&p->mnt_child);
1192                if (mnt_has_parent(p)) {
1193                        p->mnt_parent->mnt_ghosts++;
1194                        put_mountpoint(p->mnt_mp);
1195                        p->mnt_mp = NULL;
1196                }
1197                change_mnt_propagation(p, MS_PRIVATE);
1198        }
1199        list_splice(&tmp_list, &unmounted);
1200}
1201
1202static void shrink_submounts(struct mount *mnt);
1203
1204static int do_umount(struct mount *mnt, int flags)
1205{
1206        struct super_block *sb = mnt->mnt.mnt_sb;
1207        int retval;
1208
1209        retval = security_sb_umount(&mnt->mnt, flags);
1210        if (retval)
1211                return retval;
1212
1213        /*
1214         * Allow userspace to request a mountpoint be expired rather than
1215         * unmounting unconditionally. Unmount only happens if:
1216         *  (1) the mark is already set (the mark is cleared by mntput())
1217         *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1218         */
1219        if (flags & MNT_EXPIRE) {
1220                if (&mnt->mnt == current->fs->root.mnt ||
1221                    flags & (MNT_FORCE | MNT_DETACH))
1222                        return -EINVAL;
1223
1224                /*
1225                 * probably don't strictly need the lock here if we examined
1226                 * all race cases, but it's a slowpath.
1227                 */
1228                br_write_lock(&vfsmount_lock);
1229                if (mnt_get_count(mnt) != 2) {
1230                        br_write_unlock(&vfsmount_lock);
1231                        return -EBUSY;
1232                }
1233                br_write_unlock(&vfsmount_lock);
1234
1235                if (!xchg(&mnt->mnt_expiry_mark, 1))
1236                        return -EAGAIN;
1237        }
1238
1239        /*
1240         * If we may have to abort operations to get out of this
1241         * mount, and they will themselves hold resources we must
1242         * allow the fs to do things. In the Unix tradition of
1243         * 'Gee thats tricky lets do it in userspace' the umount_begin
1244         * might fail to complete on the first run through as other tasks
1245         * must return, and the like. Thats for the mount program to worry
1246         * about for the moment.
1247         */
1248
1249        if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1250                sb->s_op->umount_begin(sb);
1251        }
1252
1253        /*
1254         * No sense to grab the lock for this test, but test itself looks
1255         * somewhat bogus. Suggestions for better replacement?
1256         * Ho-hum... In principle, we might treat that as umount + switch
1257         * to rootfs. GC would eventually take care of the old vfsmount.
1258         * Actually it makes sense, especially if rootfs would contain a
1259         * /reboot - static binary that would close all descriptors and
1260         * call reboot(9). Then init(8) could umount root and exec /reboot.
1261         */
1262        if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1263                /*
1264                 * Special case for "unmounting" root ...
1265                 * we just try to remount it readonly.
1266                 */
1267                down_write(&sb->s_umount);
1268                if (!(sb->s_flags & MS_RDONLY))
1269                        retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
1270                up_write(&sb->s_umount);
1271                return retval;
1272        }
1273
1274        namespace_lock();
1275        br_write_lock(&vfsmount_lock);
1276        event++;
1277
1278        if (!(flags & MNT_DETACH))
1279                shrink_submounts(mnt);
1280
1281        retval = -EBUSY;
1282        if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
1283                if (!list_empty(&mnt->mnt_list))
1284                        umount_tree(mnt, 1);
1285                retval = 0;
1286        }
1287        br_write_unlock(&vfsmount_lock);
1288        namespace_unlock();
1289        return retval;
1290}
1291
1292/* 
1293 * Is the caller allowed to modify his namespace?
1294 */
1295static inline bool may_mount(void)
1296{
1297        return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
1298}
1299
1300/*
1301 * Now umount can handle mount points as well as block devices.
1302 * This is important for filesystems which use unnamed block devices.
1303 *
1304 * We now support a flag for forced unmount like the other 'big iron'
1305 * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1306 */
1307
1308SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1309{
1310        struct path path;
1311        struct mount *mnt;
1312        int retval;
1313        int lookup_flags = 0;
1314
1315        if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1316                return -EINVAL;
1317
1318        if (!may_mount())
1319                return -EPERM;
1320
1321        if (!(flags & UMOUNT_NOFOLLOW))
1322                lookup_flags |= LOOKUP_FOLLOW;
1323
1324        retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
1325        if (retval)
1326                goto out;
1327        mnt = real_mount(path.mnt);
1328        retval = -EINVAL;
1329        if (path.dentry != path.mnt->mnt_root)
1330                goto dput_and_out;
1331        if (!check_mnt(mnt))
1332                goto dput_and_out;
1333        if (mnt->mnt.mnt_flags & MNT_LOCKED)
1334                goto dput_and_out;
1335
1336        retval = do_umount(mnt, flags);
1337dput_and_out:
1338        /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1339        dput(path.dentry);
1340        mntput_no_expire(mnt);
1341out:
1342        return retval;
1343}
1344
1345#ifdef __ARCH_WANT_SYS_OLDUMOUNT
1346
1347/*
1348 *      The 2.0 compatible umount. No flags.
1349 */
1350SYSCALL_DEFINE1(oldumount, char __user *, name)
1351{
1352        return sys_umount(name, 0);
1353}
1354
1355#endif
1356
1357static bool is_mnt_ns_file(struct dentry *dentry)
1358{
1359        /* Is this a proxy for a mount namespace? */
1360        struct inode *inode = dentry->d_inode;
1361        struct proc_ns *ei;
1362
1363        if (!proc_ns_inode(inode))
1364                return false;
1365
1366        ei = get_proc_ns(inode);
1367        if (ei->ns_ops != &mntns_operations)
1368                return false;
1369
1370        return true;
1371}
1372
1373static bool mnt_ns_loop(struct dentry *dentry)
1374{
1375        /* Could bind mounting the mount namespace inode cause a
1376         * mount namespace loop?
1377         */
1378        struct mnt_namespace *mnt_ns;
1379        if (!is_mnt_ns_file(dentry))
1380                return false;
1381
1382        mnt_ns = get_proc_ns(dentry->d_inode)->ns;
1383        return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
1384}
1385
1386struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
1387                                        int flag)
1388{
1389        struct mount *res, *p, *q, *r, *parent;
1390
1391        if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
1392                return ERR_PTR(-EINVAL);
1393
1394        if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
1395                return ERR_PTR(-EINVAL);
1396
1397        res = q = clone_mnt(mnt, dentry, flag);
1398        if (IS_ERR(q))
1399                return q;
1400
1401        q->mnt.mnt_flags &= ~MNT_LOCKED;
1402        q->mnt_mountpoint = mnt->mnt_mountpoint;
1403
1404        p = mnt;
1405        list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1406                struct mount *s;
1407                if (!is_subdir(r->mnt_mountpoint, dentry))
1408                        continue;
1409
1410                for (s = r; s; s = next_mnt(s, r)) {
1411                        if (!(flag & CL_COPY_UNBINDABLE) &&
1412                            IS_MNT_UNBINDABLE(s)) {
1413                                s = skip_mnt_tree(s);
1414                                continue;
1415                        }
1416                        if (!(flag & CL_COPY_MNT_NS_FILE) &&
1417                            is_mnt_ns_file(s->mnt.mnt_root)) {
1418                                s = skip_mnt_tree(s);
1419                                continue;
1420                        }
1421                        while (p != s->mnt_parent) {
1422                                p = p->mnt_parent;
1423                                q = q->mnt_parent;
1424                        }
1425                        p = s;
1426                        parent = q;
1427                        q = clone_mnt(p, p->mnt.mnt_root, flag);
1428                        if (IS_ERR(q))
1429                                goto out;
1430                        br_write_lock(&vfsmount_lock);
1431                        list_add_tail(&q->mnt_list, &res->mnt_list);
1432                        attach_mnt(q, parent, p->mnt_mp);
1433                        br_write_unlock(&vfsmount_lock);
1434                }
1435        }
1436        return res;
1437out:
1438        if (res) {
1439                br_write_lock(&vfsmount_lock);
1440                umount_tree(res, 0);
1441                br_write_unlock(&vfsmount_lock);
1442        }
1443        return q;
1444}
1445
1446/* Caller should check returned pointer for errors */
1447
1448struct vfsmount *collect_mounts(struct path *path)
1449{
1450        struct mount *tree;
1451        namespace_lock();
1452        tree = copy_tree(real_mount(path->mnt), path->dentry,
1453                         CL_COPY_ALL | CL_PRIVATE);
1454        namespace_unlock();
1455        if (IS_ERR(tree))
1456                return ERR_CAST(tree);
1457        return &tree->mnt;
1458}
1459
1460void drop_collected_mounts(struct vfsmount *mnt)
1461{
1462        namespace_lock();
1463        br_write_lock(&vfsmount_lock);
1464        umount_tree(real_mount(mnt), 0);
1465        br_write_unlock(&vfsmount_lock);
1466        namespace_unlock();
1467}
1468
1469int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1470                   struct vfsmount *root)
1471{
1472        struct mount *mnt;
1473        int res = f(root, arg);
1474        if (res)
1475                return res;
1476        list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
1477                res = f(&mnt->mnt, arg);
1478                if (res)
1479                        return res;
1480        }
1481        return 0;
1482}
1483
1484static void cleanup_group_ids(struct mount *mnt, struct mount *end)
1485{
1486        struct mount *p;
1487
1488        for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1489                if (p->mnt_group_id && !IS_MNT_SHARED(p))
1490                        mnt_release_group_id(p);
1491        }
1492}
1493
1494static int invent_group_ids(struct mount *mnt, bool recurse)
1495{
1496        struct mount *p;
1497
1498        for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1499                if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1500                        int err = mnt_alloc_group_id(p);
1501                        if (err) {
1502                                cleanup_group_ids(mnt, p);
1503                                return err;
1504                        }
1505                }
1506        }
1507
1508        return 0;
1509}
1510
1511/*
1512 *  @source_mnt : mount tree to be attached
1513 *  @nd         : place the mount tree @source_mnt is attached
1514 *  @parent_nd  : if non-null, detach the source_mnt from its parent and
1515 *                 store the parent mount and mountpoint dentry.
1516 *                 (done when source_mnt is moved)
1517 *
1518 *  NOTE: in the table below explains the semantics when a source mount
1519 *  of a given type is attached to a destination mount of a given type.
1520 * ---------------------------------------------------------------------------
1521 * |         BIND MOUNT OPERATION                                            |
1522 * |**************************************************************************
1523 * | source-->| shared        |       private  |       slave    | unbindable |
1524 * | dest     |               |                |                |            |
1525 * |   |      |               |                |                |            |
1526 * |   v      |               |                |                |            |
1527 * |**************************************************************************
1528 * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
1529 * |          |               |                |                |            |
1530 * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
1531 * ***************************************************************************
1532 * A bind operation clones the source mount and mounts the clone on the
1533 * destination mount.
1534 *
1535 * (++)  the cloned mount is propagated to all the mounts in the propagation
1536 *       tree of the destination mount and the cloned mount is added to
1537 *       the peer group of the source mount.
1538 * (+)   the cloned mount is created under the destination mount and is marked
1539 *       as shared. The cloned mount is added to the peer group of the source
1540 *       mount.
1541 * (+++) the mount is propagated to all the mounts in the propagation tree
1542 *       of the destination mount and the cloned mount is made slave
1543 *       of the same master as that of the source mount. The cloned mount
1544 *       is marked as 'shared and slave'.
1545 * (*)   the cloned mount is made a slave of the same master as that of the
1546 *       source mount.
1547 *
1548 * ---------------------------------------------------------------------------
1549 * |                    MOVE MOUNT OPERATION                                 |
1550 * |**************************************************************************
1551 * | source-->| shared        |       private  |       slave    | unbindable |
1552 * | dest     |               |                |                |            |
1553 * |   |      |               |                |                |            |
1554 * |   v      |               |                |                |            |
1555 * |**************************************************************************
1556 * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
1557 * |          |               |                |                |            |
1558 * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
1559 * ***************************************************************************
1560 *
1561 * (+)  the mount is moved to the destination. And is then propagated to
1562 *      all the mounts in the propagation tree of the destination mount.
1563 * (+*)  the mount is moved to the destination.
1564 * (+++)  the mount is moved to the destination and is then propagated to
1565 *      all the mounts belonging to the destination mount's propagation tree.
1566 *      the mount is marked as 'shared and slave'.
1567 * (*)  the mount continues to be a slave at the new location.
1568 *
1569 * if the source mount is a tree, the operations explained above is
1570 * applied to each mount in the tree.
1571 * Must be called without spinlocks held, since this function can sleep
1572 * in allocations.
1573 */
1574static int attach_recursive_mnt(struct mount *source_mnt,
1575                        struct mount *dest_mnt,
1576                        struct mountpoint *dest_mp,
1577                        struct path *parent_path)
1578{
1579        LIST_HEAD(tree_list);
1580        struct mount *child, *p;
1581        int err;
1582
1583        if (IS_MNT_SHARED(dest_mnt)) {
1584                err = invent_group_ids(source_mnt, true);
1585                if (err)
1586                        goto out;
1587        }
1588        err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
1589        if (err)
1590                goto out_cleanup_ids;
1591
1592        br_write_lock(&vfsmount_lock);
1593
1594        if (IS_MNT_SHARED(dest_mnt)) {
1595                for (p = source_mnt; p; p = next_mnt(p, source_mnt))
1596                        set_mnt_shared(p);
1597        }
1598        if (parent_path) {
1599                detach_mnt(source_mnt, parent_path);
1600                attach_mnt(source_mnt, dest_mnt, dest_mp);
1601                touch_mnt_namespace(source_mnt->mnt_ns);
1602        } else {
1603                mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
1604                commit_tree(source_mnt);
1605        }
1606
1607        list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
1608                list_del_init(&child->mnt_hash);
1609                commit_tree(child);
1610        }
1611        br_write_unlock(&vfsmount_lock);
1612
1613        return 0;
1614
1615 out_cleanup_ids:
1616        if (IS_MNT_SHARED(dest_mnt))
1617                cleanup_group_ids(source_mnt, NULL);
1618 out:
1619        return err;
1620}
1621
1622static struct mountpoint *lock_mount(struct path *path)
1623{
1624        struct vfsmount *mnt;
1625        struct dentry *dentry = path->dentry;
1626retry:
1627        mutex_lock(&dentry->d_inode->i_mutex);
1628        if (unlikely(cant_mount(dentry))) {
1629                mutex_unlock(&dentry->d_inode->i_mutex);
1630                return ERR_PTR(-ENOENT);
1631        }
1632        namespace_lock();
1633        mnt = lookup_mnt(path);
1634        if (likely(!mnt)) {
1635                struct mountpoint *mp = new_mountpoint(dentry);
1636                if (IS_ERR(mp)) {
1637                        namespace_unlock();
1638                        mutex_unlock(&dentry->d_inode->i_mutex);
1639                        return mp;
1640                }
1641                return mp;
1642        }
1643        namespace_unlock();
1644        mutex_unlock(&path->dentry->d_inode->i_mutex);
1645        path_put(path);
1646        path->mnt = mnt;
1647        dentry = path->dentry = dget(mnt->mnt_root);
1648        goto retry;
1649}
1650
1651static void unlock_mount(struct mountpoint *where)
1652{
1653        struct dentry *dentry = where->m_dentry;
1654        put_mountpoint(where);
1655        namespace_unlock();
1656        mutex_unlock(&dentry->d_inode->i_mutex);
1657}
1658
1659static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
1660{
1661        if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
1662                return -EINVAL;
1663
1664        if (S_ISDIR(mp->m_dentry->d_inode->i_mode) !=
1665              S_ISDIR(mnt->mnt.mnt_root->d_inode->i_mode))
1666                return -ENOTDIR;
1667
1668        return attach_recursive_mnt(mnt, p, mp, NULL);
1669}
1670
1671/*
1672 * Sanity check the flags to change_mnt_propagation.
1673 */
1674
1675static int flags_to_propagation_type(int flags)
1676{
1677        int type = flags & ~(MS_REC | MS_SILENT);
1678
1679        /* Fail if any non-propagation flags are set */
1680        if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1681                return 0;
1682        /* Only one propagation flag should be set */
1683        if (!is_power_of_2(type))
1684                return 0;
1685        return type;
1686}
1687
1688/*
1689 * recursively change the type of the mountpoint.
1690 */
1691static int do_change_type(struct path *path, int flag)
1692{
1693        struct mount *m;
1694        struct mount *mnt = real_mount(path->mnt);
1695        int recurse = flag & MS_REC;
1696        int type;
1697        int err = 0;
1698
1699        if (path->dentry != path->mnt->mnt_root)
1700                return -EINVAL;
1701
1702        type = flags_to_propagation_type(flag);
1703        if (!type)
1704                return -EINVAL;
1705
1706        namespace_lock();
1707        if (type == MS_SHARED) {
1708                err = invent_group_ids(mnt, recurse);
1709                if (err)
1710                        goto out_unlock;
1711        }
1712
1713        br_write_lock(&vfsmount_lock);
1714        for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
1715                change_mnt_propagation(m, type);
1716        br_write_unlock(&vfsmount_lock);
1717
1718 out_unlock:
1719        namespace_unlock();
1720        return err;
1721}
1722
1723static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
1724{
1725        struct mount *child;
1726        list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
1727                if (!is_subdir(child->mnt_mountpoint, dentry))
1728                        continue;
1729
1730                if (child->mnt.mnt_flags & MNT_LOCKED)
1731                        return true;
1732        }
1733        return false;
1734}
1735
1736/*
1737 * do loopback mount.
1738 */
1739static int do_loopback(struct path *path, const char *old_name,
1740                                int recurse)
1741{
1742        struct path old_path;
1743        struct mount *mnt = NULL, *old, *parent;
1744        struct mountpoint *mp;
1745        int err;
1746        if (!old_name || !*old_name)
1747                return -EINVAL;
1748        err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
1749        if (err)
1750                return err;
1751
1752        err = -EINVAL;
1753        if (mnt_ns_loop(old_path.dentry))
1754                goto out; 
1755
1756        mp = lock_mount(path);
1757        err = PTR_ERR(mp);
1758        if (IS_ERR(mp))
1759                goto out;
1760
1761        old = real_mount(old_path.mnt);
1762        parent = real_mount(path->mnt);
1763
1764        err = -EINVAL;
1765        if (IS_MNT_UNBINDABLE(old))
1766                goto out2;
1767
1768        if (!check_mnt(parent) || !check_mnt(old))
1769                goto out2;
1770
1771        if (!recurse && has_locked_children(old, old_path.dentry))
1772                goto out2;
1773
1774        if (recurse)
1775                mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE);
1776        else
1777                mnt = clone_mnt(old, old_path.dentry, 0);
1778
1779        if (IS_ERR(mnt)) {
1780                err = PTR_ERR(mnt);
1781                goto out2;
1782        }
1783
1784        mnt->mnt.mnt_flags &= ~MNT_LOCKED;
1785
1786        err = graft_tree(mnt, parent, mp);
1787        if (err) {
1788                br_write_lock(&vfsmount_lock);
1789                umount_tree(mnt, 0);
1790                br_write_unlock(&vfsmount_lock);
1791        }
1792out2:
1793        unlock_mount(mp);
1794out:
1795        path_put(&old_path);
1796        return err;
1797}
1798
1799static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
1800{
1801        int error = 0;
1802        int readonly_request = 0;
1803
1804        if (ms_flags & MS_RDONLY)
1805                readonly_request = 1;
1806        if (readonly_request == __mnt_is_readonly(mnt))
1807                return 0;
1808
1809        if (mnt->mnt_flags & MNT_LOCK_READONLY)
1810                return -EPERM;
1811
1812        if (readonly_request)
1813                error = mnt_make_readonly(real_mount(mnt));
1814        else
1815                __mnt_unmake_readonly(real_mount(mnt));
1816        return error;
1817}
1818
1819/*
1820 * change filesystem flags. dir should be a physical root of filesystem.
1821 * If you've mounted a non-root directory somewhere and want to do remount
1822 * on it - tough luck.
1823 */
1824static int do_remount(struct path *path, int flags, int mnt_flags,
1825                      void *data)
1826{
1827        int err;
1828        struct super_block *sb = path->mnt->mnt_sb;
1829        struct mount *mnt = real_mount(path->mnt);
1830
1831        if (!check_mnt(mnt))
1832                return -EINVAL;
1833
1834        if (path->dentry != path->mnt->mnt_root)
1835                return -EINVAL;
1836
1837        err = security_sb_remount(sb, data);
1838        if (err)
1839                return err;
1840
1841        down_write(&sb->s_umount);
1842        if (flags & MS_BIND)
1843                err = change_mount_flags(path->mnt, flags);
1844        else if (!capable(CAP_SYS_ADMIN))
1845                err = -EPERM;
1846        else
1847                err = do_remount_sb(sb, flags, data, 0);
1848        if (!err) {
1849                br_write_lock(&vfsmount_lock);
1850                mnt_flags |= mnt->mnt.mnt_flags & MNT_PROPAGATION_MASK;
1851                mnt->mnt.mnt_flags = mnt_flags;
1852                br_write_unlock(&vfsmount_lock);
1853        }
1854        up_write(&sb->s_umount);
1855        if (!err) {
1856                br_write_lock(&vfsmount_lock);
1857                touch_mnt_namespace(mnt->mnt_ns);
1858                br_write_unlock(&vfsmount_lock);
1859        }
1860        return err;
1861}
1862
1863static inline int tree_contains_unbindable(struct mount *mnt)
1864{
1865        struct mount *p;
1866        for (p = mnt; p; p = next_mnt(p, mnt)) {
1867                if (IS_MNT_UNBINDABLE(p))
1868                        return 1;
1869        }
1870        return 0;
1871}
1872
1873static int do_move_mount(struct path *path, const char *old_name)
1874{
1875        struct path old_path, parent_path;
1876        struct mount *p;
1877        struct mount *old;
1878        struct mountpoint *mp;
1879        int err;
1880        if (!old_name || !*old_name)
1881                return -EINVAL;
1882        err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
1883        if (err)
1884                return err;
1885
1886        mp = lock_mount(path);
1887        err = PTR_ERR(mp);
1888        if (IS_ERR(mp))
1889                goto out;
1890
1891        old = real_mount(old_path.mnt);
1892        p = real_mount(path->mnt);
1893
1894        err = -EINVAL;
1895        if (!check_mnt(p) || !check_mnt(old))
1896                goto out1;
1897
1898        if (old->mnt.mnt_flags & MNT_LOCKED)
1899                goto out1;
1900
1901        err = -EINVAL;
1902        if (old_path.dentry != old_path.mnt->mnt_root)
1903                goto out1;
1904
1905        if (!mnt_has_parent(old))
1906                goto out1;
1907
1908        if (S_ISDIR(path->dentry->d_inode->i_mode) !=
1909              S_ISDIR(old_path.dentry->d_inode->i_mode))
1910                goto out1;
1911        /*
1912         * Don't move a mount residing in a shared parent.
1913         */
1914        if (IS_MNT_SHARED(old->mnt_parent))
1915                goto out1;
1916        /*
1917         * Don't move a mount tree containing unbindable mounts to a destination
1918         * mount which is shared.
1919         */
1920        if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
1921                goto out1;
1922        err = -ELOOP;
1923        for (; mnt_has_parent(p); p = p->mnt_parent)
1924                if (p == old)
1925                        goto out1;
1926
1927        err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
1928        if (err)
1929                goto out1;
1930
1931        /* if the mount is moved, it should no longer be expire
1932         * automatically */
1933        list_del_init(&old->mnt_expire);
1934out1:
1935        unlock_mount(mp);
1936out:
1937        if (!err)
1938                path_put(&parent_path);
1939        path_put(&old_path);
1940        return err;
1941}
1942
1943static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
1944{
1945        int err;
1946        const char *subtype = strchr(fstype, '.');
1947        if (subtype) {
1948                subtype++;
1949                err = -EINVAL;
1950                if (!subtype[0])
1951                        goto err;
1952        } else
1953                subtype = "";
1954
1955        mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
1956        err = -ENOMEM;
1957        if (!mnt->mnt_sb->s_subtype)
1958                goto err;
1959        return mnt;
1960
1961 err:
1962        mntput(mnt);
1963        return ERR_PTR(err);
1964}
1965
1966/*
1967 * add a mount into a namespace's mount tree
1968 */
1969static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
1970{
1971        struct mountpoint *mp;
1972        struct mount *parent;
1973        int err;
1974
1975        mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
1976
1977        mp = lock_mount(path);
1978        if (IS_ERR(mp))
1979                return PTR_ERR(mp);
1980
1981        parent = real_mount(path->mnt);
1982        err = -EINVAL;
1983        if (unlikely(!check_mnt(parent))) {
1984                /* that's acceptable only for automounts done in private ns */
1985                if (!(mnt_flags & MNT_SHRINKABLE))
1986                        goto unlock;
1987                /* ... and for those we'd better have mountpoint still alive */
1988                if (!parent->mnt_ns)
1989                        goto unlock;
1990        }
1991
1992        /* Refuse the same filesystem on the same mount point */
1993        err = -EBUSY;
1994        if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
1995            path->mnt->mnt_root == path->dentry)
1996                goto unlock;
1997
1998        err = -EINVAL;
1999        if (S_ISLNK(newmnt->mnt.mnt_root->d_inode->i_mode))
2000                goto unlock;
2001
2002        newmnt->mnt.mnt_flags = mnt_flags;
2003        err = graft_tree(newmnt, parent, mp);
2004
2005unlock:
2006        unlock_mount(mp);
2007        return err;
2008}
2009
2010/*
2011 * create a new mount for userspace and request it to be added into the
2012 * namespace's tree
2013 */
2014static int do_new_mount(struct path *path, const char *fstype, int flags,
2015                        int mnt_flags, const char *name, void *data)
2016{
2017        struct file_system_type *type;
2018        struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
2019        struct vfsmount *mnt;
2020        int err;
2021
2022        if (!fstype)
2023                return -EINVAL;
2024
2025        type = get_fs_type(fstype);
2026        if (!type)
2027                return -ENODEV;
2028
2029        if (user_ns != &init_user_ns) {
2030                if (!(type->fs_flags & FS_USERNS_MOUNT)) {
2031                        put_filesystem(type);
2032                        return -EPERM;
2033                }
2034                /* Only in special cases allow devices from mounts
2035                 * created outside the initial user namespace.
2036                 */
2037                if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
2038                        flags |= MS_NODEV;
2039                        mnt_flags |= MNT_NODEV;
2040                }
2041        }
2042
2043        mnt = vfs_kern_mount(type, flags, name, data);
2044        if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
2045            !mnt->mnt_sb->s_subtype)
2046                mnt = fs_set_subtype(mnt, fstype);
2047
2048        put_filesystem(type);
2049        if (IS_ERR(mnt))
2050                return PTR_ERR(mnt);
2051
2052        err = do_add_mount(real_mount(mnt), path, mnt_flags);
2053        if (err)
2054                mntput(mnt);
2055        return err;
2056}
2057
2058int finish_automount(struct vfsmount *m, struct path *path)
2059{
2060        struct mount *mnt = real_mount(m);
2061        int err;
2062        /* The new mount record should have at least 2 refs to prevent it being
2063         * expired before we get a chance to add it
2064         */
2065        BUG_ON(mnt_get_count(mnt) < 2);
2066
2067        if (m->mnt_sb == path->mnt->mnt_sb &&
2068            m->mnt_root == path->dentry) {
2069                err = -ELOOP;
2070                goto fail;
2071        }
2072
2073        err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2074        if (!err)
2075                return 0;
2076fail:
2077        /* remove m from any expiration list it may be on */
2078        if (!list_empty(&mnt->mnt_expire)) {
2079                namespace_lock();
2080                br_write_lock(&vfsmount_lock);
2081                list_del_init(&mnt->mnt_expire);
2082                br_write_unlock(&vfsmount_lock);
2083                namespace_unlock();
2084        }
2085        mntput(m);
2086        mntput(m);
2087        return err;
2088}
2089
2090/**
2091 * mnt_set_expiry - Put a mount on an expiration list
2092 * @mnt: The mount to list.
2093 * @expiry_list: The list to add the mount to.
2094 */
2095void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2096{
2097        namespace_lock();
2098        br_write_lock(&vfsmount_lock);
2099
2100        list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
2101
2102        br_write_unlock(&vfsmount_lock);
2103        namespace_unlock();
2104}
2105EXPORT_SYMBOL(mnt_set_expiry);
2106
2107/*
2108 * process a list of expirable mountpoints with the intent of discarding any
2109 * mountpoints that aren't in use and haven't been touched since last we came
2110 * here
2111 */
2112void mark_mounts_for_expiry(struct list_head *mounts)
2113{
2114        struct mount *mnt, *next;
2115        LIST_HEAD(graveyard);
2116
2117        if (list_empty(mounts))
2118                return;
2119
2120        namespace_lock();
2121        br_write_lock(&vfsmount_lock);
2122
2123        /* extract from the expiration list every vfsmount that matches the
2124         * following criteria:
2125         * - only referenced by its parent vfsmount
2126         * - still marked for expiry (marked on the last call here; marks are
2127         *   cleared by mntput())
2128         */
2129        list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2130                if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2131                        propagate_mount_busy(mnt, 1))
2132                        continue;
2133                list_move(&mnt->mnt_expire, &graveyard);
2134        }
2135        while (!list_empty(&graveyard)) {
2136                mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
2137                touch_mnt_namespace(mnt->mnt_ns);
2138                umount_tree(mnt, 1);
2139        }
2140        br_write_unlock(&vfsmount_lock);
2141        namespace_unlock();
2142}
2143
2144EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2145
2146/*
2147 * Ripoff of 'select_parent()'
2148 *
2149 * search the list of submounts for a given mountpoint, and move any
2150 * shrinkable submounts to the 'graveyard' list.
2151 */
2152static int select_submounts(struct mount *parent, struct list_head *graveyard)
2153{
2154        struct mount *this_parent = parent;
2155        struct list_head *next;
2156        int found = 0;
2157
2158repeat:
2159        next = this_parent->mnt_mounts.next;
2160resume:
2161        while (next != &this_parent->mnt_mounts) {
2162                struct list_head *tmp = next;
2163                struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
2164
2165                next = tmp->next;
2166                if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
2167                        continue;
2168                /*
2169                 * Descend a level if the d_mounts list is non-empty.
2170                 */
2171                if (!list_empty(&mnt->mnt_mounts)) {
2172                        this_parent = mnt;
2173                        goto repeat;
2174                }
2175
2176                if (!propagate_mount_busy(mnt, 1)) {
2177                        list_move_tail(&mnt->mnt_expire, graveyard);
2178                        found++;
2179                }
2180        }
2181        /*
2182         * All done at this level ... ascend and resume the search
2183         */
2184        if (this_parent != parent) {
2185                next = this_parent->mnt_child.next;
2186                this_parent = this_parent->mnt_parent;
2187                goto resume;
2188        }
2189        return found;
2190}
2191
2192/*
2193 * process a list of expirable mountpoints with the intent of discarding any
2194 * submounts of a specific parent mountpoint
2195 *
2196 * vfsmount_lock must be held for write
2197 */
2198static void shrink_submounts(struct mount *mnt)
2199{
2200        LIST_HEAD(graveyard);
2201        struct mount *m;
2202
2203        /* extract submounts of 'mountpoint' from the expiration list */
2204        while (select_submounts(mnt, &graveyard)) {
2205                while (!list_empty(&graveyard)) {
2206                        m = list_first_entry(&graveyard, struct mount,
2207                                                mnt_expire);
2208                        touch_mnt_namespace(m->mnt_ns);
2209                        umount_tree(m, 1);
2210                }
2211        }
2212}
2213
2214/*
2215 * Some copy_from_user() implementations do not return the exact number of
2216 * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
2217 * Note that this function differs from copy_from_user() in that it will oops
2218 * on bad values of `to', rather than returning a short copy.
2219 */
2220static long exact_copy_from_user(void *to, const void __user * from,
2221                                 unsigned long n)
2222{
2223        char *t = to;
2224        const char __user *f = from;
2225        char c;
2226
2227        if (!access_ok(VERIFY_READ, from, n))
2228                return n;
2229
2230        while (n) {
2231                if (__get_user(c, f)) {
2232                        memset(t, 0, n);
2233                        break;
2234                }
2235                *t++ = c;
2236                f++;
2237                n--;
2238        }
2239        return n;
2240}
2241
2242int copy_mount_options(const void __user * data, unsigned long *where)
2243{
2244        int i;
2245        unsigned long page;
2246        unsigned long size;
2247
2248        *where = 0;
2249        if (!data)
2250                return 0;
2251
2252        if (!(page = __get_free_page(GFP_KERNEL)))
2253                return -ENOMEM;
2254
2255        /* We only care that *some* data at the address the user
2256         * gave us is valid.  Just in case, we'll zero
2257         * the remainder of the page.
2258         */
2259        /* copy_from_user cannot cross TASK_SIZE ! */
2260        size = TASK_SIZE - (unsigned long)data;
2261        if (size > PAGE_SIZE)
2262                size = PAGE_SIZE;
2263
2264        i = size - exact_copy_from_user((void *)page, data, size);
2265        if (!i) {
2266                free_page(page);
2267                return -EFAULT;
2268        }
2269        if (i != PAGE_SIZE)
2270                memset((char *)page + i, 0, PAGE_SIZE - i);
2271        *where = page;
2272        return 0;
2273}
2274
2275int copy_mount_string(const void __user *data, char **where)
2276{
2277        char *tmp;
2278
2279        if (!data) {
2280                *where = NULL;
2281                return 0;
2282        }
2283
2284        tmp = strndup_user(data, PAGE_SIZE);
2285        if (IS_ERR(tmp))
2286                return PTR_ERR(tmp);
2287
2288        *where = tmp;
2289        return 0;
2290}
2291
2292/*
2293 * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
2294 * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
2295 *
2296 * data is a (void *) that can point to any structure up to
2297 * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
2298 * information (or be NULL).
2299 *
2300 * Pre-0.97 versions of mount() didn't have a flags word.
2301 * When the flags word was introduced its top half was required
2302 * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
2303 * Therefore, if this magic number is present, it carries no information
2304 * and must be discarded.
2305 */
2306long do_mount(const char *dev_name, const char *dir_name,
2307                const char *type_page, unsigned long flags, void *data_page)
2308{
2309        struct path path;
2310        int retval = 0;
2311        int mnt_flags = 0;
2312
2313        /* Discard magic */
2314        if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
2315                flags &= ~MS_MGC_MSK;
2316
2317        /* Basic sanity checks */
2318
2319        if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
2320                return -EINVAL;
2321
2322        if (data_page)
2323                ((char *)data_page)[PAGE_SIZE - 1] = 0;
2324
2325        /* ... and get the mountpoint */
2326        retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
2327        if (retval)
2328                return retval;
2329
2330        retval = security_sb_mount(dev_name, &path,
2331                                   type_page, flags, data_page);
2332        if (!retval && !may_mount())
2333                retval = -EPERM;
2334        if (retval)
2335                goto dput_out;
2336
2337        /* Default to relatime unless overriden */
2338        if (!(flags & MS_NOATIME))
2339                mnt_flags |= MNT_RELATIME;
2340
2341        /* Separate the per-mountpoint flags */
2342        if (flags & MS_NOSUID)
2343                mnt_flags |= MNT_NOSUID;
2344        if (flags & MS_NODEV)
2345                mnt_flags |= MNT_NODEV;
2346        if (flags & MS_NOEXEC)
2347                mnt_flags |= MNT_NOEXEC;
2348        if (flags & MS_NOATIME)
2349                mnt_flags |= MNT_NOATIME;
2350        if (flags & MS_NODIRATIME)
2351                mnt_flags |= MNT_NODIRATIME;
2352        if (flags & MS_STRICTATIME)
2353                mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
2354        if (flags & MS_RDONLY)
2355                mnt_flags |= MNT_READONLY;
2356
2357        flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
2358                   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
2359                   MS_STRICTATIME);
2360
2361        if (flags & MS_REMOUNT)
2362                retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
2363                                    data_page);
2364        else if (flags & MS_BIND)
2365                retval = do_loopback(&path, dev_name, flags & MS_REC);
2366        else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2367                retval = do_change_type(&path, flags);
2368        else if (flags & MS_MOVE)
2369                retval = do_move_mount(&path, dev_name);
2370        else
2371                retval = do_new_mount(&path, type_page, flags, mnt_flags,
2372                                      dev_name, data_page);
2373dput_out:
2374        path_put(&path);
2375        return retval;
2376}
2377
2378static void free_mnt_ns(struct mnt_namespace *ns)
2379{
2380        proc_free_inum(ns->proc_inum);
2381        put_user_ns(ns->user_ns);
2382        kfree(ns);
2383}
2384
2385/*
2386 * Assign a sequence number so we can detect when we attempt to bind
2387 * mount a reference to an older mount namespace into the current
2388 * mount namespace, preventing reference counting loops.  A 64bit
2389 * number incrementing at 10Ghz will take 12,427 years to wrap which
2390 * is effectively never, so we can ignore the possibility.
2391 */
2392static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
2393
2394static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
2395{
2396        struct mnt_namespace *new_ns;
2397        int ret;
2398
2399        new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
2400        if (!new_ns)
2401                return ERR_PTR(-ENOMEM);
2402        ret = proc_alloc_inum(&new_ns->proc_inum);
2403        if (ret) {
2404                kfree(new_ns);
2405                return ERR_PTR(ret);
2406        }
2407        new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
2408        atomic_set(&new_ns->count, 1);
2409        new_ns->root = NULL;
2410        INIT_LIST_HEAD(&new_ns->list);
2411        init_waitqueue_head(&new_ns->poll);
2412        new_ns->event = 0;
2413        new_ns->user_ns = get_user_ns(user_ns);
2414        return new_ns;
2415}
2416
2417/*
2418 * Allocate a new namespace structure and populate it with contents
2419 * copied from the namespace of the passed in task structure.
2420 */
2421static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
2422                struct user_namespace *user_ns, struct fs_struct *fs)
2423{
2424        struct mnt_namespace *new_ns;
2425        struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
2426        struct mount *p, *q;
2427        struct mount *old = mnt_ns->root;
2428        struct mount *new;
2429        int copy_flags;
2430
2431        new_ns = alloc_mnt_ns(user_ns);
2432        if (IS_ERR(new_ns))
2433                return new_ns;
2434
2435        namespace_lock();
2436        /* First pass: copy the tree topology */
2437        copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
2438        if (user_ns != mnt_ns->user_ns)
2439                copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
2440        new = copy_tree(old, old->mnt.mnt_root, copy_flags);
2441        if (IS_ERR(new)) {
2442                namespace_unlock();
2443                free_mnt_ns(new_ns);
2444                return ERR_CAST(new);
2445        }
2446        new_ns->root = new;
2447        br_write_lock(&vfsmount_lock);
2448        list_add_tail(&new_ns->list, &new->mnt_list);
2449        br_write_unlock(&vfsmount_lock);
2450
2451        /*
2452         * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
2453         * as belonging to new namespace.  We have already acquired a private
2454         * fs_struct, so tsk->fs->lock is not needed.
2455         */
2456        p = old;
2457        q = new;
2458        while (p) {
2459                q->mnt_ns = new_ns;
2460                if (fs) {
2461                        if (&p->mnt == fs->root.mnt) {
2462                                fs->root.mnt = mntget(&q->mnt);
2463                                rootmnt = &p->mnt;
2464                        }
2465                        if (&p->mnt == fs->pwd.mnt) {
2466                                fs->pwd.mnt = mntget(&q->mnt);
2467                                pwdmnt = &p->mnt;
2468                        }
2469                }
2470                p = next_mnt(p, old);
2471                q = next_mnt(q, new);
2472                if (!q)
2473                        break;
2474                while (p->mnt.mnt_root != q->mnt.mnt_root)
2475                        p = next_mnt(p, old);
2476        }
2477        namespace_unlock();
2478
2479        if (rootmnt)
2480                mntput(rootmnt);
2481        if (pwdmnt)
2482                mntput(pwdmnt);
2483
2484        return new_ns;
2485}
2486
2487struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
2488                struct user_namespace *user_ns, struct fs_struct *new_fs)
2489{
2490        struct mnt_namespace *new_ns;
2491
2492        BUG_ON(!ns);
2493        get_mnt_ns(ns);
2494
2495        if (!(flags & CLONE_NEWNS))
2496                return ns;
2497
2498        new_ns = dup_mnt_ns(ns, user_ns, new_fs);
2499
2500        put_mnt_ns(ns);
2501        return new_ns;
2502}
2503
2504/**
2505 * create_mnt_ns - creates a private namespace and adds a root filesystem
2506 * @mnt: pointer to the new root filesystem mountpoint
2507 */
2508static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
2509{
2510        struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
2511        if (!IS_ERR(new_ns)) {
2512                struct mount *mnt = real_mount(m);
2513                mnt->mnt_ns = new_ns;
2514                new_ns->root = mnt;
2515                list_add(&mnt->mnt_list, &new_ns->list);
2516        } else {
2517                mntput(m);
2518        }
2519        return new_ns;
2520}
2521
2522struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
2523{
2524        struct mnt_namespace *ns;
2525        struct super_block *s;
2526        struct path path;
2527        int err;
2528
2529        ns = create_mnt_ns(mnt);
2530        if (IS_ERR(ns))
2531                return ERR_CAST(ns);
2532
2533        err = vfs_path_lookup(mnt->mnt_root, mnt,
2534                        name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
2535
2536        put_mnt_ns(ns);
2537
2538        if (err)
2539                return ERR_PTR(err);
2540
2541        /* trade a vfsmount reference for active sb one */
2542        s = path.mnt->mnt_sb;
2543        atomic_inc(&s->s_active);
2544        mntput(path.mnt);
2545        /* lock the sucker */
2546        down_write(&s->s_umount);
2547        /* ... and return the root of (sub)tree on it */
2548        return path.dentry;
2549}
2550EXPORT_SYMBOL(mount_subtree);
2551
2552SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
2553                char __user *, type, unsigned long, flags, void __user *, data)
2554{
2555        int ret;
2556        char *kernel_type;
2557        struct filename *kernel_dir;
2558        char *kernel_dev;
2559        unsigned long data_page;
2560
2561        ret = copy_mount_string(type, &kernel_type);
2562        if (ret < 0)
2563                goto out_type;
2564
2565        kernel_dir = getname(dir_name);
2566        if (IS_ERR(kernel_dir)) {
2567                ret = PTR_ERR(kernel_dir);
2568                goto out_dir;
2569        }
2570
2571        ret = copy_mount_string(dev_name, &kernel_dev);
2572        if (ret < 0)
2573                goto out_dev;
2574
2575        ret = copy_mount_options(data, &data_page);
2576        if (ret < 0)
2577                goto out_data;
2578
2579        ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags,
2580                (void *) data_page);
2581
2582        free_page(data_page);
2583out_data:
2584        kfree(kernel_dev);
2585out_dev:
2586        putname(kernel_dir);
2587out_dir:
2588        kfree(kernel_type);
2589out_type:
2590        return ret;
2591}
2592
2593/*
2594 * Return true if path is reachable from root
2595 *
2596 * namespace_sem or vfsmount_lock is held
2597 */
2598bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
2599                         const struct path *root)
2600{
2601        while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
2602                dentry = mnt->mnt_mountpoint;
2603                mnt = mnt->mnt_parent;
2604        }
2605        return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
2606}
2607
2608int path_is_under(struct path *path1, struct path *path2)
2609{
2610        int res;
2611        br_read_lock(&vfsmount_lock);
2612        res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
2613        br_read_unlock(&vfsmount_lock);
2614        return res;
2615}
2616EXPORT_SYMBOL(path_is_under);
2617
2618/*
2619 * pivot_root Semantics:
2620 * Moves the root file system of the current process to the directory put_old,
2621 * makes new_root as the new root file system of the current process, and sets
2622 * root/cwd of all processes which had them on the current root to new_root.
2623 *
2624 * Restrictions:
2625 * The new_root and put_old must be directories, and  must not be on the
2626 * same file  system as the current process root. The put_old  must  be
2627 * underneath new_root,  i.e. adding a non-zero number of /.. to the string
2628 * pointed to by put_old must yield the same directory as new_root. No other
2629 * file system may be mounted on put_old. After all, new_root is a mountpoint.
2630 *
2631 * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
2632 * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
2633 * in this situation.
2634 *
2635 * Notes:
2636 *  - we don't move root/cwd if they are not at the root (reason: if something
2637 *    cared enough to change them, it's probably wrong to force them elsewhere)
2638 *  - it's okay to pick a root that isn't the root of a file system, e.g.
2639 *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
2640 *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
2641 *    first.
2642 */
2643SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
2644                const char __user *, put_old)
2645{
2646        struct path new, old, parent_path, root_parent, root;
2647        struct mount *new_mnt, *root_mnt, *old_mnt;
2648        struct mountpoint *old_mp, *root_mp;
2649        int error;
2650
2651        if (!may_mount())
2652                return -EPERM;
2653
2654        error = user_path_dir(new_root, &new);
2655        if (error)
2656                goto out0;
2657
2658        error = user_path_dir(put_old, &old);
2659        if (error)
2660                goto out1;
2661
2662        error = security_sb_pivotroot(&old, &new);
2663        if (error)
2664                goto out2;
2665
2666        get_fs_root(current->fs, &root);
2667        old_mp = lock_mount(&old);
2668        error = PTR_ERR(old_mp);
2669        if (IS_ERR(old_mp))
2670                goto out3;
2671
2672        error = -EINVAL;
2673        new_mnt = real_mount(new.mnt);
2674        root_mnt = real_mount(root.mnt);
2675        old_mnt = real_mount(old.mnt);
2676        if (IS_MNT_SHARED(old_mnt) ||
2677                IS_MNT_SHARED(new_mnt->mnt_parent) ||
2678                IS_MNT_SHARED(root_mnt->mnt_parent))
2679                goto out4;
2680        if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
2681                goto out4;
2682        if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
2683                goto out4;
2684        error = -ENOENT;
2685        if (d_unlinked(new.dentry))
2686                goto out4;
2687        error = -EBUSY;
2688        if (new_mnt == root_mnt || old_mnt == root_mnt)
2689                goto out4; /* loop, on the same file system  */
2690        error = -EINVAL;
2691        if (root.mnt->mnt_root != root.dentry)
2692                goto out4; /* not a mountpoint */
2693        if (!mnt_has_parent(root_mnt))
2694                goto out4; /* not attached */
2695        root_mp = root_mnt->mnt_mp;
2696        if (new.mnt->mnt_root != new.dentry)
2697                goto out4; /* not a mountpoint */
2698        if (!mnt_has_parent(new_mnt))
2699                goto out4; /* not attached */
2700        /* make sure we can reach put_old from new_root */
2701        if (!is_path_reachable(old_mnt, old.dentry, &new))
2702                goto out4;
2703        root_mp->m_count++; /* pin it so it won't go away */
2704        br_write_lock(&vfsmount_lock);
2705        detach_mnt(new_mnt, &parent_path);
2706        detach_mnt(root_mnt, &root_parent);
2707        if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
2708                new_mnt->mnt.mnt_flags |= MNT_LOCKED;
2709                root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
2710        }
2711        /* mount old root on put_old */
2712        attach_mnt(root_mnt, old_mnt, old_mp);
2713        /* mount new_root on / */
2714        attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
2715        touch_mnt_namespace(current->nsproxy->mnt_ns);
2716        br_write_unlock(&vfsmount_lock);
2717        chroot_fs_refs(&root, &new);
2718        put_mountpoint(root_mp);
2719        error = 0;
2720out4:
2721        unlock_mount(old_mp);
2722        if (!error) {
2723                path_put(&root_parent);
2724                path_put(&parent_path);
2725        }
2726out3:
2727        path_put(&root);
2728out2:
2729        path_put(&old);
2730out1:
2731        path_put(&new);
2732out0:
2733        return error;
2734}
2735
2736static void __init init_mount_tree(void)
2737{
2738        struct vfsmount *mnt;
2739        struct mnt_namespace *ns;
2740        struct path root;
2741        struct file_system_type *type;
2742
2743        type = get_fs_type("rootfs");
2744        if (!type)
2745                panic("Can't find rootfs type");
2746        mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
2747        put_filesystem(type);
2748        if (IS_ERR(mnt))
2749                panic("Can't create rootfs");
2750
2751        ns = create_mnt_ns(mnt);
2752        if (IS_ERR(ns))
2753                panic("Can't allocate initial namespace");
2754
2755        init_task.nsproxy->mnt_ns = ns;
2756        get_mnt_ns(ns);
2757
2758        root.mnt = mnt;
2759        root.dentry = mnt->mnt_root;
2760
2761        set_fs_pwd(current->fs, &root);
2762        set_fs_root(current->fs, &root);
2763}
2764
2765void __init mnt_init(void)
2766{
2767        unsigned u;
2768        int err;
2769
2770        init_rwsem(&namespace_sem);
2771
2772        mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
2773                        0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2774
2775        mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
2776        mountpoint_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
2777
2778        if (!mount_hashtable || !mountpoint_hashtable)
2779                panic("Failed to allocate mount hash table\n");
2780
2781        printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
2782
2783        for (u = 0; u < HASH_SIZE; u++)
2784                INIT_LIST_HEAD(&mount_hashtable[u]);
2785        for (u = 0; u < HASH_SIZE; u++)
2786                INIT_LIST_HEAD(&mountpoint_hashtable[u]);
2787
2788        br_lock_init(&vfsmount_lock);
2789
2790        err = sysfs_init();
2791        if (err)
2792                printk(KERN_WARNING "%s: sysfs_init error: %d\n",
2793                        __func__, err);
2794        fs_kobj = kobject_create_and_add("fs", NULL);
2795        if (!fs_kobj)
2796                printk(KERN_WARNING "%s: kobj create error\n", __func__);
2797        init_rootfs();
2798        init_mount_tree();
2799}
2800
2801void put_mnt_ns(struct mnt_namespace *ns)
2802{
2803        if (!atomic_dec_and_test(&ns->count))
2804                return;
2805        namespace_lock();
2806        br_write_lock(&vfsmount_lock);
2807        umount_tree(ns->root, 0);
2808        br_write_unlock(&vfsmount_lock);
2809        namespace_unlock();
2810        free_mnt_ns(ns);
2811}
2812
2813struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
2814{
2815        struct vfsmount *mnt;
2816        mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
2817        if (!IS_ERR(mnt)) {
2818                /*
2819                 * it is a longterm mount, don't release mnt until
2820                 * we unmount before file sys is unregistered
2821                */
2822                real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
2823        }
2824        return mnt;
2825}
2826EXPORT_SYMBOL_GPL(kern_mount_data);
2827
2828void kern_unmount(struct vfsmount *mnt)
2829{
2830        /* release long term mount so mount point can be released */
2831        if (!IS_ERR_OR_NULL(mnt)) {
2832                br_write_lock(&vfsmount_lock);
2833                real_mount(mnt)->mnt_ns = NULL;
2834                br_write_unlock(&vfsmount_lock);
2835                mntput(mnt);
2836        }
2837}
2838EXPORT_SYMBOL(kern_unmount);
2839
2840bool our_mnt(struct vfsmount *mnt)
2841{
2842        return check_mnt(real_mount(mnt));
2843}
2844
2845bool current_chrooted(void)
2846{
2847        /* Does the current process have a non-standard root */
2848        struct path ns_root;
2849        struct path fs_root;
2850        bool chrooted;
2851
2852        /* Find the namespace root */
2853        ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
2854        ns_root.dentry = ns_root.mnt->mnt_root;
2855        path_get(&ns_root);
2856        while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
2857                ;
2858
2859        get_fs_root(current->fs, &fs_root);
2860
2861        chrooted = !path_equal(&fs_root, &ns_root);
2862
2863        path_put(&fs_root);
2864        path_put(&ns_root);
2865
2866        return chrooted;
2867}
2868
2869bool fs_fully_visible(struct file_system_type *type)
2870{
2871        struct mnt_namespace *ns = current->nsproxy->mnt_ns;
2872        struct mount *mnt;
2873        bool visible = false;
2874
2875        if (unlikely(!ns))
2876                return false;
2877
2878        namespace_lock();
2879        list_for_each_entry(mnt, &ns->list, mnt_list) {
2880                struct mount *child;
2881                if (mnt->mnt.mnt_sb->s_type != type)
2882                        continue;
2883
2884                /* This mount is not fully visible if there are any child mounts
2885                 * that cover anything except for empty directories.
2886                 */
2887                list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
2888                        struct inode *inode = child->mnt_mountpoint->d_inode;
2889                        if (!S_ISDIR(inode->i_mode))
2890                                goto next;
2891                        if (inode->i_nlink != 2)
2892                                goto next;
2893                }
2894                visible = true;
2895                goto found;
2896        next:   ;
2897        }
2898found:
2899        namespace_unlock();
2900        return visible;
2901}
2902
2903static void *mntns_get(struct task_struct *task)
2904{
2905        struct mnt_namespace *ns = NULL;
2906        struct nsproxy *nsproxy;
2907
2908        rcu_read_lock();
2909        nsproxy = task_nsproxy(task);
2910        if (nsproxy) {
2911                ns = nsproxy->mnt_ns;
2912                get_mnt_ns(ns);
2913        }
2914        rcu_read_unlock();
2915
2916        return ns;
2917}
2918
2919static void mntns_put(void *ns)
2920{
2921        put_mnt_ns(ns);
2922}
2923
2924static int mntns_install(struct nsproxy *nsproxy, void *ns)
2925{
2926        struct fs_struct *fs = current->fs;
2927        struct mnt_namespace *mnt_ns = ns;
2928        struct path root;
2929
2930        if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
2931            !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
2932            !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
2933                return -EPERM;
2934
2935        if (fs->users != 1)
2936                return -EINVAL;
2937
2938        get_mnt_ns(mnt_ns);
2939        put_mnt_ns(nsproxy->mnt_ns);
2940        nsproxy->mnt_ns = mnt_ns;
2941
2942        /* Find the root */
2943        root.mnt    = &mnt_ns->root->mnt;
2944        root.dentry = mnt_ns->root->mnt.mnt_root;
2945        path_get(&root);
2946        while(d_mountpoint(root.dentry) && follow_down_one(&root))
2947                ;
2948
2949        /* Update the pwd and root */
2950        set_fs_pwd(fs, &root);
2951        set_fs_root(fs, &root);
2952
2953        path_put(&root);
2954        return 0;
2955}
2956
2957static unsigned int mntns_inum(void *ns)
2958{
2959        struct mnt_namespace *mnt_ns = ns;
2960        return mnt_ns->proc_inum;
2961}
2962
2963const struct proc_ns_operations mntns_operations = {
2964        .name           = "mnt",
2965        .type           = CLONE_NEWNS,
2966        .get            = mntns_get,
2967        .put            = mntns_put,
2968        .install        = mntns_install,
2969        .inum           = mntns_inum,
2970};
2971
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