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/ramfs.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
 615        list_for_each_entry(mp, chain, m_hash) {
 616                if (mp->m_dentry == dentry) {
 617                        /* might be worth a WARN_ON() */
 618                        if (d_unlinked(dentry))
 619                                return ERR_PTR(-ENOENT);
 620                        mp->m_count++;
 621                        return mp;
 622                }
 623        }
 624
 625        mp = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
 626        if (!mp)
 627                return ERR_PTR(-ENOMEM);
 628
 629        spin_lock(&dentry->d_lock);
 630        if (d_unlinked(dentry)) {
 631                spin_unlock(&dentry->d_lock);
 632                kfree(mp);
 633                return ERR_PTR(-ENOENT);
 634        }
 635        dentry->d_flags |= DCACHE_MOUNTED;
 636        spin_unlock(&dentry->d_lock);
 637        mp->m_dentry = dentry;
 638        mp->m_count = 1;
 639        list_add(&mp->m_hash, chain);
 640        return mp;
 641}
 642
 643static void put_mountpoint(struct mountpoint *mp)
 644{
 645        if (!--mp->m_count) {
 646                struct dentry *dentry = mp->m_dentry;
 647                spin_lock(&dentry->d_lock);
 648                dentry->d_flags &= ~DCACHE_MOUNTED;
 649                spin_unlock(&dentry->d_lock);
 650                list_del(&mp->m_hash);
 651                kfree(mp);
 652        }
 653}
 654
 655static inline int check_mnt(struct mount *mnt)
 656{
 657        return mnt->mnt_ns == current->nsproxy->mnt_ns;
 658}
 659
 660/*
 661 * vfsmount lock must be held for write
 662 */
 663static void touch_mnt_namespace(struct mnt_namespace *ns)
 664{
 665        if (ns) {
 666                ns->event = ++event;
 667                wake_up_interruptible(&ns->poll);
 668        }
 669}
 670
 671/*
 672 * vfsmount lock must be held for write
 673 */
 674static void __touch_mnt_namespace(struct mnt_namespace *ns)
 675{
 676        if (ns && ns->event != event) {
 677                ns->event = event;
 678                wake_up_interruptible(&ns->poll);
 679        }
 680}
 681
 682/*
 683 * vfsmount lock must be held for write
 684 */
 685static void detach_mnt(struct mount *mnt, struct path *old_path)
 686{
 687        old_path->dentry = mnt->mnt_mountpoint;
 688        old_path->mnt = &mnt->mnt_parent->mnt;
 689        mnt->mnt_parent = mnt;
 690        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 691        list_del_init(&mnt->mnt_child);
 692        list_del_init(&mnt->mnt_hash);
 693        put_mountpoint(mnt->mnt_mp);
 694        mnt->mnt_mp = NULL;
 695}
 696
 697/*
 698 * vfsmount lock must be held for write
 699 */
 700void mnt_set_mountpoint(struct mount *mnt,
 701                        struct mountpoint *mp,
 702                        struct mount *child_mnt)
 703{
 704        mp->m_count++;
 705        mnt_add_count(mnt, 1);  /* essentially, that's mntget */
 706        child_mnt->mnt_mountpoint = dget(mp->m_dentry);
 707        child_mnt->mnt_parent = mnt;
 708        child_mnt->mnt_mp = mp;
 709}
 710
 711/*
 712 * vfsmount lock must be held for write
 713 */
 714static void attach_mnt(struct mount *mnt,
 715                        struct mount *parent,
 716                        struct mountpoint *mp)
 717{
 718        mnt_set_mountpoint(parent, mp, mnt);
 719        list_add_tail(&mnt->mnt_hash, mount_hashtable +
 720                        hash(&parent->mnt, mp->m_dentry));
 721        list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 722}
 723
 724/*
 725 * vfsmount lock must be held for write
 726 */
 727static void commit_tree(struct mount *mnt)
 728{
 729        struct mount *parent = mnt->mnt_parent;
 730        struct mount *m;
 731        LIST_HEAD(head);
 732        struct mnt_namespace *n = parent->mnt_ns;
 733
 734        BUG_ON(parent == mnt);
 735
 736        list_add_tail(&head, &mnt->mnt_list);
 737        list_for_each_entry(m, &head, mnt_list)
 738                m->mnt_ns = n;
 739
 740        list_splice(&head, n->list.prev);
 741
 742        list_add_tail(&mnt->mnt_hash, mount_hashtable +
 743                                hash(&parent->mnt, mnt->mnt_mountpoint));
 744        list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 745        touch_mnt_namespace(n);
 746}
 747
 748static struct mount *next_mnt(struct mount *p, struct mount *root)
 749{
 750        struct list_head *next = p->mnt_mounts.next;
 751        if (next == &p->mnt_mounts) {
 752                while (1) {
 753                        if (p == root)
 754                                return NULL;
 755                        next = p->mnt_child.next;
 756                        if (next != &p->mnt_parent->mnt_mounts)
 757                                break;
 758                        p = p->mnt_parent;
 759                }
 760        }
 761        return list_entry(next, struct mount, mnt_child);
 762}
 763
 764static struct mount *skip_mnt_tree(struct mount *p)
 765{
 766        struct list_head *prev = p->mnt_mounts.prev;
 767        while (prev != &p->mnt_mounts) {
 768                p = list_entry(prev, struct mount, mnt_child);
 769                prev = p->mnt_mounts.prev;
 770        }
 771        return p;
 772}
 773
 774struct vfsmount *
 775vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
 776{
 777        struct mount *mnt;
 778        struct dentry *root;
 779
 780        if (!type)
 781                return ERR_PTR(-ENODEV);
 782
 783        mnt = alloc_vfsmnt(name);
 784        if (!mnt)
 785                return ERR_PTR(-ENOMEM);
 786
 787        if (flags & MS_KERNMOUNT)
 788                mnt->mnt.mnt_flags = MNT_INTERNAL;
 789
 790        root = mount_fs(type, flags, name, data);
 791        if (IS_ERR(root)) {
 792                free_vfsmnt(mnt);
 793                return ERR_CAST(root);
 794        }
 795
 796        mnt->mnt.mnt_root = root;
 797        mnt->mnt.mnt_sb = root->d_sb;
 798        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 799        mnt->mnt_parent = mnt;
 800        br_write_lock(&vfsmount_lock);
 801        list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
 802        br_write_unlock(&vfsmount_lock);
 803        return &mnt->mnt;
 804}
 805EXPORT_SYMBOL_GPL(vfs_kern_mount);
 806
 807static struct mount *clone_mnt(struct mount *old, struct dentry *root,
 808                                        int flag)
 809{
 810        struct super_block *sb = old->mnt.mnt_sb;
 811        struct mount *mnt;
 812        int err;
 813
 814        mnt = alloc_vfsmnt(old->mnt_devname);
 815        if (!mnt)
 816                return ERR_PTR(-ENOMEM);
 817
 818        if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
 819                mnt->mnt_group_id = 0; /* not a peer of original */
 820        else
 821                mnt->mnt_group_id = old->mnt_group_id;
 822
 823        if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
 824                err = mnt_alloc_group_id(mnt);
 825                if (err)
 826                        goto out_free;
 827        }
 828
 829        mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~MNT_WRITE_HOLD;
 830        /* Don't allow unprivileged users to change mount flags */
 831        if ((flag & CL_UNPRIVILEGED) && (mnt->mnt.mnt_flags & MNT_READONLY))
 832                mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
 833
 834        atomic_inc(&sb->s_active);
 835        mnt->mnt.mnt_sb = sb;
 836        mnt->mnt.mnt_root = dget(root);
 837        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 838        mnt->mnt_parent = mnt;
 839        br_write_lock(&vfsmount_lock);
 840        list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
 841        br_write_unlock(&vfsmount_lock);
 842
 843        if ((flag & CL_SLAVE) ||
 844            ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
 845                list_add(&mnt->mnt_slave, &old->mnt_slave_list);
 846                mnt->mnt_master = old;
 847                CLEAR_MNT_SHARED(mnt);
 848        } else if (!(flag & CL_PRIVATE)) {
 849                if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
 850                        list_add(&mnt->mnt_share, &old->mnt_share);
 851                if (IS_MNT_SLAVE(old))
 852                        list_add(&mnt->mnt_slave, &old->mnt_slave);
 853                mnt->mnt_master = old->mnt_master;
 854        }
 855        if (flag & CL_MAKE_SHARED)
 856                set_mnt_shared(mnt);
 857
 858        /* stick the duplicate mount on the same expiry list
 859         * as the original if that was on one */
 860        if (flag & CL_EXPIRE) {
 861                if (!list_empty(&old->mnt_expire))
 862                        list_add(&mnt->mnt_expire, &old->mnt_expire);
 863        }
 864
 865        return mnt;
 866
 867 out_free:
 868        free_vfsmnt(mnt);
 869        return ERR_PTR(err);
 870}
 871
 872static inline void mntfree(struct mount *mnt)
 873{
 874        struct vfsmount *m = &mnt->mnt;
 875        struct super_block *sb = m->mnt_sb;
 876
 877        /*
 878         * This probably indicates that somebody messed
 879         * up a mnt_want/drop_write() pair.  If this
 880         * happens, the filesystem was probably unable
 881         * to make r/w->r/o transitions.
 882         */
 883        /*
 884         * The locking used to deal with mnt_count decrement provides barriers,
 885         * so mnt_get_writers() below is safe.
 886         */
 887        WARN_ON(mnt_get_writers(mnt));
 888        fsnotify_vfsmount_delete(m);
 889        dput(m->mnt_root);
 890        free_vfsmnt(mnt);
 891        deactivate_super(sb);
 892}
 893
 894static void mntput_no_expire(struct mount *mnt)
 895{
 896put_again:
 897#ifdef CONFIG_SMP
 898        br_read_lock(&vfsmount_lock);
 899        if (likely(mnt->mnt_ns)) {
 900                /* shouldn't be the last one */
 901                mnt_add_count(mnt, -1);
 902                br_read_unlock(&vfsmount_lock);
 903                return;
 904        }
 905        br_read_unlock(&vfsmount_lock);
 906
 907        br_write_lock(&vfsmount_lock);
 908        mnt_add_count(mnt, -1);
 909        if (mnt_get_count(mnt)) {
 910                br_write_unlock(&vfsmount_lock);
 911                return;
 912        }
 913#else
 914        mnt_add_count(mnt, -1);
 915        if (likely(mnt_get_count(mnt)))
 916                return;
 917        br_write_lock(&vfsmount_lock);
 918#endif
 919        if (unlikely(mnt->mnt_pinned)) {
 920                mnt_add_count(mnt, mnt->mnt_pinned + 1);
 921                mnt->mnt_pinned = 0;
 922                br_write_unlock(&vfsmount_lock);
 923                acct_auto_close_mnt(&mnt->mnt);
 924                goto put_again;
 925        }
 926
 927        list_del(&mnt->mnt_instance);
 928        br_write_unlock(&vfsmount_lock);
 929        mntfree(mnt);
 930}
 931
 932void mntput(struct vfsmount *mnt)
 933{
 934        if (mnt) {
 935                struct mount *m = real_mount(mnt);
 936                /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
 937                if (unlikely(m->mnt_expiry_mark))
 938                        m->mnt_expiry_mark = 0;
 939                mntput_no_expire(m);
 940        }
 941}
 942EXPORT_SYMBOL(mntput);
 943
 944struct vfsmount *mntget(struct vfsmount *mnt)
 945{
 946        if (mnt)
 947                mnt_add_count(real_mount(mnt), 1);
 948        return mnt;
 949}
 950EXPORT_SYMBOL(mntget);
 951
 952void mnt_pin(struct vfsmount *mnt)
 953{
 954        br_write_lock(&vfsmount_lock);
 955        real_mount(mnt)->mnt_pinned++;
 956        br_write_unlock(&vfsmount_lock);
 957}
 958EXPORT_SYMBOL(mnt_pin);
 959
 960void mnt_unpin(struct vfsmount *m)
 961{
 962        struct mount *mnt = real_mount(m);
 963        br_write_lock(&vfsmount_lock);
 964        if (mnt->mnt_pinned) {
 965                mnt_add_count(mnt, 1);
 966                mnt->mnt_pinned--;
 967        }
 968        br_write_unlock(&vfsmount_lock);
 969}
 970EXPORT_SYMBOL(mnt_unpin);
 971
 972static inline void mangle(struct seq_file *m, const char *s)
 973{
 974        seq_escape(m, s, " \t\n\\");
 975}
 976
 977/*
 978 * Simple .show_options callback for filesystems which don't want to
 979 * implement more complex mount option showing.
 980 *
 981 * See also save_mount_options().
 982 */
 983int generic_show_options(struct seq_file *m, struct dentry *root)
 984{
 985        const char *options;
 986
 987        rcu_read_lock();
 988        options = rcu_dereference(root->d_sb->s_options);
 989
 990        if (options != NULL && options[0]) {
 991                seq_putc(m, ',');
 992                mangle(m, options);
 993        }
 994        rcu_read_unlock();
 995
 996        return 0;
 997}
 998EXPORT_SYMBOL(generic_show_options);
 999
1000/*
1001 * If filesystem uses generic_show_options(), this function should be
1002 * called from the fill_super() callback.
1003 *
1004 * The .remount_fs callback usually needs to be handled in a special
1005 * way, to make sure, that previous options are not overwritten if the
1006 * remount fails.
1007 *
1008 * Also note, that if the filesystem's .remount_fs function doesn't
1009 * reset all options to their default value, but changes only newly
1010 * given options, then the displayed options will not reflect reality
1011 * any more.
1012 */
1013void save_mount_options(struct super_block *sb, char *options)
1014{
1015        BUG_ON(sb->s_options);
1016        rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
1017}
1018EXPORT_SYMBOL(save_mount_options);
1019
1020void replace_mount_options(struct super_block *sb, char *options)
1021{
1022        char *old = sb->s_options;
1023        rcu_assign_pointer(sb->s_options, options);
1024        if (old) {
1025                synchronize_rcu();
1026                kfree(old);
1027        }
1028}
1029EXPORT_SYMBOL(replace_mount_options);
1030
1031#ifdef CONFIG_PROC_FS
1032/* iterator; we want it to have access to namespace_sem, thus here... */
1033static void *m_start(struct seq_file *m, loff_t *pos)
1034{
1035        struct proc_mounts *p = proc_mounts(m);
1036
1037        down_read(&namespace_sem);
1038        return seq_list_start(&p->ns->list, *pos);
1039}
1040
1041static void *m_next(struct seq_file *m, void *v, loff_t *pos)
1042{
1043        struct proc_mounts *p = proc_mounts(m);
1044
1045        return seq_list_next(v, &p->ns->list, pos);
1046}
1047
1048static void m_stop(struct seq_file *m, void *v)
1049{
1050        up_read(&namespace_sem);
1051}
1052
1053static int m_show(struct seq_file *m, void *v)
1054{
1055        struct proc_mounts *p = proc_mounts(m);
1056        struct mount *r = list_entry(v, struct mount, mnt_list);
1057        return p->show(m, &r->mnt);
1058}
1059
1060const struct seq_operations mounts_op = {
1061        .start  = m_start,
1062        .next   = m_next,
1063        .stop   = m_stop,
1064        .show   = m_show,
1065};
1066#endif  /* CONFIG_PROC_FS */
1067
1068/**
1069 * may_umount_tree - check if a mount tree is busy
1070 * @mnt: root of mount tree
1071 *
1072 * This is called to check if a tree of mounts has any
1073 * open files, pwds, chroots or sub mounts that are
1074 * busy.
1075 */
1076int may_umount_tree(struct vfsmount *m)
1077{
1078        struct mount *mnt = real_mount(m);
1079        int actual_refs = 0;
1080        int minimum_refs = 0;
1081        struct mount *p;
1082        BUG_ON(!m);
1083
1084        /* write lock needed for mnt_get_count */
1085        br_write_lock(&vfsmount_lock);
1086        for (p = mnt; p; p = next_mnt(p, mnt)) {
1087                actual_refs += mnt_get_count(p);
1088                minimum_refs += 2;
1089        }
1090        br_write_unlock(&vfsmount_lock);
1091
1092        if (actual_refs > minimum_refs)
1093                return 0;
1094
1095        return 1;
1096}
1097
1098EXPORT_SYMBOL(may_umount_tree);
1099
1100/**
1101 * may_umount - check if a mount point is busy
1102 * @mnt: root of mount
1103 *
1104 * This is called to check if a mount point has any
1105 * open files, pwds, chroots or sub mounts. If the
1106 * mount has sub mounts this will return busy
1107 * regardless of whether the sub mounts are busy.
1108 *
1109 * Doesn't take quota and stuff into account. IOW, in some cases it will
1110 * give false negatives. The main reason why it's here is that we need
1111 * a non-destructive way to look for easily umountable filesystems.
1112 */
1113int may_umount(struct vfsmount *mnt)
1114{
1115        int ret = 1;
1116        down_read(&namespace_sem);
1117        br_write_lock(&vfsmount_lock);
1118        if (propagate_mount_busy(real_mount(mnt), 2))
1119                ret = 0;
1120        br_write_unlock(&vfsmount_lock);
1121        up_read(&namespace_sem);
1122        return ret;
1123}
1124
1125EXPORT_SYMBOL(may_umount);
1126
1127static LIST_HEAD(unmounted);    /* protected by namespace_sem */
1128
1129static void namespace_unlock(void)
1130{
1131        struct mount *mnt;
1132        LIST_HEAD(head);
1133
1134        if (likely(list_empty(&unmounted))) {
1135                up_write(&namespace_sem);
1136                return;
1137        }
1138
1139        list_splice_init(&unmounted, &head);
1140        up_write(&namespace_sem);
1141
1142        while (!list_empty(&head)) {
1143                mnt = list_first_entry(&head, struct mount, mnt_hash);
1144                list_del_init(&mnt->mnt_hash);
1145                if (mnt_has_parent(mnt)) {
1146                        struct dentry *dentry;
1147                        struct mount *m;
1148
1149                        br_write_lock(&vfsmount_lock);
1150                        dentry = mnt->mnt_mountpoint;
1151                        m = mnt->mnt_parent;
1152                        mnt->mnt_mountpoint = mnt->mnt.mnt_root;
1153                        mnt->mnt_parent = mnt;
1154                        m->mnt_ghosts--;
1155                        br_write_unlock(&vfsmount_lock);
1156                        dput(dentry);
1157                        mntput(&m->mnt);
1158                }
1159                mntput(&mnt->mnt);
1160        }
1161}
1162
1163static inline void namespace_lock(void)
1164{
1165        down_write(&namespace_sem);
1166}
1167
1168/*
1169 * vfsmount lock must be held for write
1170 * namespace_sem must be held for write
1171 */
1172void umount_tree(struct mount *mnt, int propagate)
1173{
1174        LIST_HEAD(tmp_list);
1175        struct mount *p;
1176
1177        for (p = mnt; p; p = next_mnt(p, mnt))
1178                list_move(&p->mnt_hash, &tmp_list);
1179
1180        if (propagate)
1181                propagate_umount(&tmp_list);
1182
1183        list_for_each_entry(p, &tmp_list, mnt_hash) {
1184                list_del_init(&p->mnt_expire);
1185                list_del_init(&p->mnt_list);
1186                __touch_mnt_namespace(p->mnt_ns);
1187                p->mnt_ns = NULL;
1188                list_del_init(&p->mnt_child);
1189                if (mnt_has_parent(p)) {
1190                        p->mnt_parent->mnt_ghosts++;
1191                        put_mountpoint(p->mnt_mp);
1192                        p->mnt_mp = NULL;
1193                }
1194                change_mnt_propagation(p, MS_PRIVATE);
1195        }
1196        list_splice(&tmp_list, &unmounted);
1197}
1198
1199static void shrink_submounts(struct mount *mnt);
1200
1201static int do_umount(struct mount *mnt, int flags)
1202{
1203        struct super_block *sb = mnt->mnt.mnt_sb;
1204        int retval;
1205
1206        retval = security_sb_umount(&mnt->mnt, flags);
1207        if (retval)
1208                return retval;
1209
1210        /*
1211         * Allow userspace to request a mountpoint be expired rather than
1212         * unmounting unconditionally. Unmount only happens if:
1213         *  (1) the mark is already set (the mark is cleared by mntput())
1214         *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1215         */
1216        if (flags & MNT_EXPIRE) {
1217                if (&mnt->mnt == current->fs->root.mnt ||
1218                    flags & (MNT_FORCE | MNT_DETACH))
1219                        return -EINVAL;
1220
1221                /*
1222                 * probably don't strictly need the lock here if we examined
1223                 * all race cases, but it's a slowpath.
1224                 */
1225                br_write_lock(&vfsmount_lock);
1226                if (mnt_get_count(mnt) != 2) {
1227                        br_write_unlock(&vfsmount_lock);
1228                        return -EBUSY;
1229                }
1230                br_write_unlock(&vfsmount_lock);
1231
1232                if (!xchg(&mnt->mnt_expiry_mark, 1))
1233                        return -EAGAIN;
1234        }
1235
1236        /*
1237         * If we may have to abort operations to get out of this
1238         * mount, and they will themselves hold resources we must
1239         * allow the fs to do things. In the Unix tradition of
1240         * 'Gee thats tricky lets do it in userspace' the umount_begin
1241         * might fail to complete on the first run through as other tasks
1242         * must return, and the like. Thats for the mount program to worry
1243         * about for the moment.
1244         */
1245
1246        if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1247                sb->s_op->umount_begin(sb);
1248        }
1249
1250        /*
1251         * No sense to grab the lock for this test, but test itself looks
1252         * somewhat bogus. Suggestions for better replacement?
1253         * Ho-hum... In principle, we might treat that as umount + switch
1254         * to rootfs. GC would eventually take care of the old vfsmount.
1255         * Actually it makes sense, especially if rootfs would contain a
1256         * /reboot - static binary that would close all descriptors and
1257         * call reboot(9). Then init(8) could umount root and exec /reboot.
1258         */
1259        if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1260                /*
1261                 * Special case for "unmounting" root ...
1262                 * we just try to remount it readonly.
1263                 */
1264                down_write(&sb->s_umount);
1265                if (!(sb->s_flags & MS_RDONLY))
1266                        retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
1267                up_write(&sb->s_umount);
1268                return retval;
1269        }
1270
1271        namespace_lock();
1272        br_write_lock(&vfsmount_lock);
1273        event++;
1274
1275        if (!(flags & MNT_DETACH))
1276                shrink_submounts(mnt);
1277
1278        retval = -EBUSY;
1279        if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
1280                if (!list_empty(&mnt->mnt_list))
1281                        umount_tree(mnt, 1);
1282                retval = 0;
1283        }
1284        br_write_unlock(&vfsmount_lock);
1285        namespace_unlock();
1286        return retval;
1287}
1288
1289/* 
1290 * Is the caller allowed to modify his namespace?
1291 */
1292static inline bool may_mount(void)
1293{
1294        return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
1295}
1296
1297/*
1298 * Now umount can handle mount points as well as block devices.
1299 * This is important for filesystems which use unnamed block devices.
1300 *
1301 * We now support a flag for forced unmount like the other 'big iron'
1302 * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1303 */
1304
1305SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1306{
1307        struct path path;
1308        struct mount *mnt;
1309        int retval;
1310        int lookup_flags = 0;
1311
1312        if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1313                return -EINVAL;
1314
1315        if (!may_mount())
1316                return -EPERM;
1317
1318        if (!(flags & UMOUNT_NOFOLLOW))
1319                lookup_flags |= LOOKUP_FOLLOW;
1320
1321        retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
1322        if (retval)
1323                goto out;
1324        mnt = real_mount(path.mnt);
1325        retval = -EINVAL;
1326        if (path.dentry != path.mnt->mnt_root)
1327                goto dput_and_out;
1328        if (!check_mnt(mnt))
1329                goto dput_and_out;
1330
1331        retval = do_umount(mnt, flags);
1332dput_and_out:
1333        /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1334        dput(path.dentry);
1335        mntput_no_expire(mnt);
1336out:
1337        return retval;
1338}
1339
1340#ifdef __ARCH_WANT_SYS_OLDUMOUNT
1341
1342/*
1343 *      The 2.0 compatible umount. No flags.
1344 */
1345SYSCALL_DEFINE1(oldumount, char __user *, name)
1346{
1347        return sys_umount(name, 0);
1348}
1349
1350#endif
1351
1352static bool mnt_ns_loop(struct path *path)
1353{
1354        /* Could bind mounting the mount namespace inode cause a
1355         * mount namespace loop?
1356         */
1357        struct inode *inode = path->dentry->d_inode;
1358        struct proc_ns *ei;
1359        struct mnt_namespace *mnt_ns;
1360
1361        if (!proc_ns_inode(inode))
1362                return false;
1363
1364        ei = get_proc_ns(inode);
1365        if (ei->ns_ops != &mntns_operations)
1366                return false;
1367
1368        mnt_ns = ei->ns;
1369        return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
1370}
1371
1372struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
1373                                        int flag)
1374{
1375        struct mount *res, *p, *q, *r, *parent;
1376
1377        if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
1378                return ERR_PTR(-EINVAL);
1379
1380        res = q = clone_mnt(mnt, dentry, flag);
1381        if (IS_ERR(q))
1382                return q;
1383
1384        q->mnt_mountpoint = mnt->mnt_mountpoint;
1385
1386        p = mnt;
1387        list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1388                struct mount *s;
1389                if (!is_subdir(r->mnt_mountpoint, dentry))
1390                        continue;
1391
1392                for (s = r; s; s = next_mnt(s, r)) {
1393                        if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
1394                                s = skip_mnt_tree(s);
1395                                continue;
1396                        }
1397                        while (p != s->mnt_parent) {
1398                                p = p->mnt_parent;
1399                                q = q->mnt_parent;
1400                        }
1401                        p = s;
1402                        parent = q;
1403                        q = clone_mnt(p, p->mnt.mnt_root, flag);
1404                        if (IS_ERR(q))
1405                                goto out;
1406                        br_write_lock(&vfsmount_lock);
1407                        list_add_tail(&q->mnt_list, &res->mnt_list);
1408                        attach_mnt(q, parent, p->mnt_mp);
1409                        br_write_unlock(&vfsmount_lock);
1410                }
1411        }
1412        return res;
1413out:
1414        if (res) {
1415                br_write_lock(&vfsmount_lock);
1416                umount_tree(res, 0);
1417                br_write_unlock(&vfsmount_lock);
1418        }
1419        return q;
1420}
1421
1422/* Caller should check returned pointer for errors */
1423
1424struct vfsmount *collect_mounts(struct path *path)
1425{
1426        struct mount *tree;
1427        namespace_lock();
1428        tree = copy_tree(real_mount(path->mnt), path->dentry,
1429                         CL_COPY_ALL | CL_PRIVATE);
1430        namespace_unlock();
1431        if (IS_ERR(tree))
1432                return ERR_CAST(tree);
1433        return &tree->mnt;
1434}
1435
1436void drop_collected_mounts(struct vfsmount *mnt)
1437{
1438        namespace_lock();
1439        br_write_lock(&vfsmount_lock);
1440        umount_tree(real_mount(mnt), 0);
1441        br_write_unlock(&vfsmount_lock);
1442        namespace_unlock();
1443}
1444
1445int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1446                   struct vfsmount *root)
1447{
1448        struct mount *mnt;
1449        int res = f(root, arg);
1450        if (res)
1451                return res;
1452        list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
1453                res = f(&mnt->mnt, arg);
1454                if (res)
1455                        return res;
1456        }
1457        return 0;
1458}
1459
1460static void cleanup_group_ids(struct mount *mnt, struct mount *end)
1461{
1462        struct mount *p;
1463
1464        for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1465                if (p->mnt_group_id && !IS_MNT_SHARED(p))
1466                        mnt_release_group_id(p);
1467        }
1468}
1469
1470static int invent_group_ids(struct mount *mnt, bool recurse)
1471{
1472        struct mount *p;
1473
1474        for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1475                if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1476                        int err = mnt_alloc_group_id(p);
1477                        if (err) {
1478                                cleanup_group_ids(mnt, p);
1479                                return err;
1480                        }
1481                }
1482        }
1483
1484        return 0;
1485}
1486
1487/*
1488 *  @source_mnt : mount tree to be attached
1489 *  @nd         : place the mount tree @source_mnt is attached
1490 *  @parent_nd  : if non-null, detach the source_mnt from its parent and
1491 *                 store the parent mount and mountpoint dentry.
1492 *                 (done when source_mnt is moved)
1493 *
1494 *  NOTE: in the table below explains the semantics when a source mount
1495 *  of a given type is attached to a destination mount of a given type.
1496 * ---------------------------------------------------------------------------
1497 * |         BIND MOUNT OPERATION                                            |
1498 * |**************************************************************************
1499 * | source-->| shared        |       private  |       slave    | unbindable |
1500 * | dest     |               |                |                |            |
1501 * |   |      |               |                |                |            |
1502 * |   v      |               |                |                |            |
1503 * |**************************************************************************
1504 * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
1505 * |          |               |                |                |            |
1506 * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
1507 * ***************************************************************************
1508 * A bind operation clones the source mount and mounts the clone on the
1509 * destination mount.
1510 *
1511 * (++)  the cloned mount is propagated to all the mounts in the propagation
1512 *       tree of the destination mount and the cloned mount is added to
1513 *       the peer group of the source mount.
1514 * (+)   the cloned mount is created under the destination mount and is marked
1515 *       as shared. The cloned mount is added to the peer group of the source
1516 *       mount.
1517 * (+++) the mount is propagated to all the mounts in the propagation tree
1518 *       of the destination mount and the cloned mount is made slave
1519 *       of the same master as that of the source mount. The cloned mount
1520 *       is marked as 'shared and slave'.
1521 * (*)   the cloned mount is made a slave of the same master as that of the
1522 *       source mount.
1523 *
1524 * ---------------------------------------------------------------------------
1525 * |                    MOVE MOUNT OPERATION                                 |
1526 * |**************************************************************************
1527 * | source-->| shared        |       private  |       slave    | unbindable |
1528 * | dest     |               |                |                |            |
1529 * |   |      |               |                |                |            |
1530 * |   v      |               |                |                |            |
1531 * |**************************************************************************
1532 * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
1533 * |          |               |                |                |            |
1534 * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
1535 * ***************************************************************************
1536 *
1537 * (+)  the mount is moved to the destination. And is then propagated to
1538 *      all the mounts in the propagation tree of the destination mount.
1539 * (+*)  the mount is moved to the destination.
1540 * (+++)  the mount is moved to the destination and is then propagated to
1541 *      all the mounts belonging to the destination mount's propagation tree.
1542 *      the mount is marked as 'shared and slave'.
1543 * (*)  the mount continues to be a slave at the new location.
1544 *
1545 * if the source mount is a tree, the operations explained above is
1546 * applied to each mount in the tree.
1547 * Must be called without spinlocks held, since this function can sleep
1548 * in allocations.
1549 */
1550static int attach_recursive_mnt(struct mount *source_mnt,
1551                        struct mount *dest_mnt,
1552                        struct mountpoint *dest_mp,
1553                        struct path *parent_path)
1554{
1555        LIST_HEAD(tree_list);
1556        struct mount *child, *p;
1557        int err;
1558
1559        if (IS_MNT_SHARED(dest_mnt)) {
1560                err = invent_group_ids(source_mnt, true);
1561                if (err)
1562                        goto out;
1563        }
1564        err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
1565        if (err)
1566                goto out_cleanup_ids;
1567
1568        br_write_lock(&vfsmount_lock);
1569
1570        if (IS_MNT_SHARED(dest_mnt)) {
1571                for (p = source_mnt; p; p = next_mnt(p, source_mnt))
1572                        set_mnt_shared(p);
1573        }
1574        if (parent_path) {
1575                detach_mnt(source_mnt, parent_path);
1576                attach_mnt(source_mnt, dest_mnt, dest_mp);
1577                touch_mnt_namespace(source_mnt->mnt_ns);
1578        } else {
1579                mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
1580                commit_tree(source_mnt);
1581        }
1582
1583        list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
1584                list_del_init(&child->mnt_hash);
1585                commit_tree(child);
1586        }
1587        br_write_unlock(&vfsmount_lock);
1588
1589        return 0;
1590
1591 out_cleanup_ids:
1592        if (IS_MNT_SHARED(dest_mnt))
1593                cleanup_group_ids(source_mnt, NULL);
1594 out:
1595        return err;
1596}
1597
1598static struct mountpoint *lock_mount(struct path *path)
1599{
1600        struct vfsmount *mnt;
1601        struct dentry *dentry = path->dentry;
1602retry:
1603        mutex_lock(&dentry->d_inode->i_mutex);
1604        if (unlikely(cant_mount(dentry))) {
1605                mutex_unlock(&dentry->d_inode->i_mutex);
1606                return ERR_PTR(-ENOENT);
1607        }
1608        namespace_lock();
1609        mnt = lookup_mnt(path);
1610        if (likely(!mnt)) {
1611                struct mountpoint *mp = new_mountpoint(dentry);
1612                if (IS_ERR(mp)) {
1613                        namespace_unlock();
1614                        mutex_unlock(&dentry->d_inode->i_mutex);
1615                        return mp;
1616                }
1617                return mp;
1618        }
1619        namespace_unlock();
1620        mutex_unlock(&path->dentry->d_inode->i_mutex);
1621        path_put(path);
1622        path->mnt = mnt;
1623        dentry = path->dentry = dget(mnt->mnt_root);
1624        goto retry;
1625}
1626
1627static void unlock_mount(struct mountpoint *where)
1628{
1629        struct dentry *dentry = where->m_dentry;
1630        put_mountpoint(where);
1631        namespace_unlock();
1632        mutex_unlock(&dentry->d_inode->i_mutex);
1633}
1634
1635static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
1636{
1637        if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
1638                return -EINVAL;
1639
1640        if (S_ISDIR(mp->m_dentry->d_inode->i_mode) !=
1641              S_ISDIR(mnt->mnt.mnt_root->d_inode->i_mode))
1642                return -ENOTDIR;
1643
1644        return attach_recursive_mnt(mnt, p, mp, NULL);
1645}
1646
1647/*
1648 * Sanity check the flags to change_mnt_propagation.
1649 */
1650
1651static int flags_to_propagation_type(int flags)
1652{
1653        int type = flags & ~(MS_REC | MS_SILENT);
1654
1655        /* Fail if any non-propagation flags are set */
1656        if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1657                return 0;
1658        /* Only one propagation flag should be set */
1659        if (!is_power_of_2(type))
1660                return 0;
1661        return type;
1662}
1663
1664/*
1665 * recursively change the type of the mountpoint.
1666 */
1667static int do_change_type(struct path *path, int flag)
1668{
1669        struct mount *m;
1670        struct mount *mnt = real_mount(path->mnt);
1671        int recurse = flag & MS_REC;
1672        int type;
1673        int err = 0;
1674
1675        if (path->dentry != path->mnt->mnt_root)
1676                return -EINVAL;
1677
1678        type = flags_to_propagation_type(flag);
1679        if (!type)
1680                return -EINVAL;
1681
1682        namespace_lock();
1683        if (type == MS_SHARED) {
1684                err = invent_group_ids(mnt, recurse);
1685                if (err)
1686                        goto out_unlock;
1687        }
1688
1689        br_write_lock(&vfsmount_lock);
1690        for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
1691                change_mnt_propagation(m, type);
1692        br_write_unlock(&vfsmount_lock);
1693
1694 out_unlock:
1695        namespace_unlock();
1696        return err;
1697}
1698
1699/*
1700 * do loopback mount.
1701 */
1702static int do_loopback(struct path *path, const char *old_name,
1703                                int recurse)
1704{
1705        struct path old_path;
1706        struct mount *mnt = NULL, *old, *parent;
1707        struct mountpoint *mp;
1708        int err;
1709        if (!old_name || !*old_name)
1710                return -EINVAL;
1711        err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
1712        if (err)
1713                return err;
1714
1715        err = -EINVAL;
1716        if (mnt_ns_loop(&old_path))
1717                goto out; 
1718
1719        mp = lock_mount(path);
1720        err = PTR_ERR(mp);
1721        if (IS_ERR(mp))
1722                goto out;
1723
1724        old = real_mount(old_path.mnt);
1725        parent = real_mount(path->mnt);
1726
1727        err = -EINVAL;
1728        if (IS_MNT_UNBINDABLE(old))
1729                goto out2;
1730
1731        if (!check_mnt(parent) || !check_mnt(old))
1732                goto out2;
1733
1734        if (recurse)
1735                mnt = copy_tree(old, old_path.dentry, 0);
1736        else
1737                mnt = clone_mnt(old, old_path.dentry, 0);
1738
1739        if (IS_ERR(mnt)) {
1740                err = PTR_ERR(mnt);
1741                goto out2;
1742        }
1743
1744        err = graft_tree(mnt, parent, mp);
1745        if (err) {
1746                br_write_lock(&vfsmount_lock);
1747                umount_tree(mnt, 0);
1748                br_write_unlock(&vfsmount_lock);
1749        }
1750out2:
1751        unlock_mount(mp);
1752out:
1753        path_put(&old_path);
1754        return err;
1755}
1756
1757static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
1758{
1759        int error = 0;
1760        int readonly_request = 0;
1761
1762        if (ms_flags & MS_RDONLY)
1763                readonly_request = 1;
1764        if (readonly_request == __mnt_is_readonly(mnt))
1765                return 0;
1766
1767        if (mnt->mnt_flags & MNT_LOCK_READONLY)
1768                return -EPERM;
1769
1770        if (readonly_request)
1771                error = mnt_make_readonly(real_mount(mnt));
1772        else
1773                __mnt_unmake_readonly(real_mount(mnt));
1774        return error;
1775}
1776
1777/*
1778 * change filesystem flags. dir should be a physical root of filesystem.
1779 * If you've mounted a non-root directory somewhere and want to do remount
1780 * on it - tough luck.
1781 */
1782static int do_remount(struct path *path, int flags, int mnt_flags,
1783                      void *data)
1784{
1785        int err;
1786        struct super_block *sb = path->mnt->mnt_sb;
1787        struct mount *mnt = real_mount(path->mnt);
1788
1789        if (!check_mnt(mnt))
1790                return -EINVAL;
1791
1792        if (path->dentry != path->mnt->mnt_root)
1793                return -EINVAL;
1794
1795        err = security_sb_remount(sb, data);
1796        if (err)
1797                return err;
1798
1799        down_write(&sb->s_umount);
1800        if (flags & MS_BIND)
1801                err = change_mount_flags(path->mnt, flags);
1802        else if (!capable(CAP_SYS_ADMIN))
1803                err = -EPERM;
1804        else
1805                err = do_remount_sb(sb, flags, data, 0);
1806        if (!err) {
1807                br_write_lock(&vfsmount_lock);
1808                mnt_flags |= mnt->mnt.mnt_flags & MNT_PROPAGATION_MASK;
1809                mnt->mnt.mnt_flags = mnt_flags;
1810                br_write_unlock(&vfsmount_lock);
1811        }
1812        up_write(&sb->s_umount);
1813        if (!err) {
1814                br_write_lock(&vfsmount_lock);
1815                touch_mnt_namespace(mnt->mnt_ns);
1816                br_write_unlock(&vfsmount_lock);
1817        }
1818        return err;
1819}
1820
1821static inline int tree_contains_unbindable(struct mount *mnt)
1822{
1823        struct mount *p;
1824        for (p = mnt; p; p = next_mnt(p, mnt)) {
1825                if (IS_MNT_UNBINDABLE(p))
1826                        return 1;
1827        }
1828        return 0;
1829}
1830
1831static int do_move_mount(struct path *path, const char *old_name)
1832{
1833        struct path old_path, parent_path;
1834        struct mount *p;
1835        struct mount *old;
1836        struct mountpoint *mp;
1837        int err;
1838        if (!old_name || !*old_name)
1839                return -EINVAL;
1840        err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
1841        if (err)
1842                return err;
1843
1844        mp = lock_mount(path);
1845        err = PTR_ERR(mp);
1846        if (IS_ERR(mp))
1847                goto out;
1848
1849        old = real_mount(old_path.mnt);
1850        p = real_mount(path->mnt);
1851
1852        err = -EINVAL;
1853        if (!check_mnt(p) || !check_mnt(old))
1854                goto out1;
1855
1856        err = -EINVAL;
1857        if (old_path.dentry != old_path.mnt->mnt_root)
1858                goto out1;
1859
1860        if (!mnt_has_parent(old))
1861                goto out1;
1862
1863        if (S_ISDIR(path->dentry->d_inode->i_mode) !=
1864              S_ISDIR(old_path.dentry->d_inode->i_mode))
1865                goto out1;
1866        /*
1867         * Don't move a mount residing in a shared parent.
1868         */
1869        if (IS_MNT_SHARED(old->mnt_parent))
1870                goto out1;
1871        /*
1872         * Don't move a mount tree containing unbindable mounts to a destination
1873         * mount which is shared.
1874         */
1875        if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
1876                goto out1;
1877        err = -ELOOP;
1878        for (; mnt_has_parent(p); p = p->mnt_parent)
1879                if (p == old)
1880                        goto out1;
1881
1882        err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
1883        if (err)
1884                goto out1;
1885
1886        /* if the mount is moved, it should no longer be expire
1887         * automatically */
1888        list_del_init(&old->mnt_expire);
1889out1:
1890        unlock_mount(mp);
1891out:
1892        if (!err)
1893                path_put(&parent_path);
1894        path_put(&old_path);
1895        return err;
1896}
1897
1898static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
1899{
1900        int err;
1901        const char *subtype = strchr(fstype, '.');
1902        if (subtype) {
1903                subtype++;
1904                err = -EINVAL;
1905                if (!subtype[0])
1906                        goto err;
1907        } else
1908                subtype = "";
1909
1910        mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
1911        err = -ENOMEM;
1912        if (!mnt->mnt_sb->s_subtype)
1913                goto err;
1914        return mnt;
1915
1916 err:
1917        mntput(mnt);
1918        return ERR_PTR(err);
1919}
1920
1921/*
1922 * add a mount into a namespace's mount tree
1923 */
1924static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
1925{
1926        struct mountpoint *mp;
1927        struct mount *parent;
1928        int err;
1929
1930        mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
1931
1932        mp = lock_mount(path);
1933        if (IS_ERR(mp))
1934                return PTR_ERR(mp);
1935
1936        parent = real_mount(path->mnt);
1937        err = -EINVAL;
1938        if (unlikely(!check_mnt(parent))) {
1939                /* that's acceptable only for automounts done in private ns */
1940                if (!(mnt_flags & MNT_SHRINKABLE))
1941                        goto unlock;
1942                /* ... and for those we'd better have mountpoint still alive */
1943                if (!parent->mnt_ns)
1944                        goto unlock;
1945        }
1946
1947        /* Refuse the same filesystem on the same mount point */
1948        err = -EBUSY;
1949        if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
1950            path->mnt->mnt_root == path->dentry)
1951                goto unlock;
1952
1953        err = -EINVAL;
1954        if (S_ISLNK(newmnt->mnt.mnt_root->d_inode->i_mode))
1955                goto unlock;
1956
1957        newmnt->mnt.mnt_flags = mnt_flags;
1958        err = graft_tree(newmnt, parent, mp);
1959
1960unlock:
1961        unlock_mount(mp);
1962        return err;
1963}
1964
1965/*
1966 * create a new mount for userspace and request it to be added into the
1967 * namespace's tree
1968 */
1969static int do_new_mount(struct path *path, const char *fstype, int flags,
1970                        int mnt_flags, const char *name, void *data)
1971{
1972        struct file_system_type *type;
1973        struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
1974        struct vfsmount *mnt;
1975        int err;
1976
1977        if (!fstype)
1978                return -EINVAL;
1979
1980        type = get_fs_type(fstype);
1981        if (!type)
1982                return -ENODEV;
1983
1984        if (user_ns != &init_user_ns) {
1985                if (!(type->fs_flags & FS_USERNS_MOUNT)) {
1986                        put_filesystem(type);
1987                        return -EPERM;
1988                }
1989                /* Only in special cases allow devices from mounts
1990                 * created outside the initial user namespace.
1991                 */
1992                if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
1993                        flags |= MS_NODEV;
1994                        mnt_flags |= MNT_NODEV;
1995                }
1996        }
1997
1998        mnt = vfs_kern_mount(type, flags, name, data);
1999        if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
2000            !mnt->mnt_sb->s_subtype)
2001                mnt = fs_set_subtype(mnt, fstype);
2002
2003        put_filesystem(type);
2004        if (IS_ERR(mnt))
2005                return PTR_ERR(mnt);
2006
2007        err = do_add_mount(real_mount(mnt), path, mnt_flags);
2008        if (err)
2009                mntput(mnt);
2010        return err;
2011}
2012
2013int finish_automount(struct vfsmount *m, struct path *path)
2014{
2015        struct mount *mnt = real_mount(m);
2016        int err;
2017        /* The new mount record should have at least 2 refs to prevent it being
2018         * expired before we get a chance to add it
2019         */
2020        BUG_ON(mnt_get_count(mnt) < 2);
2021
2022        if (m->mnt_sb == path->mnt->mnt_sb &&
2023            m->mnt_root == path->dentry) {
2024                err = -ELOOP;
2025                goto fail;
2026        }
2027
2028        err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2029        if (!err)
2030                return 0;
2031fail:
2032        /* remove m from any expiration list it may be on */
2033        if (!list_empty(&mnt->mnt_expire)) {
2034                namespace_lock();
2035                br_write_lock(&vfsmount_lock);
2036                list_del_init(&mnt->mnt_expire);
2037                br_write_unlock(&vfsmount_lock);
2038                namespace_unlock();
2039        }
2040        mntput(m);
2041        mntput(m);
2042        return err;
2043}
2044
2045/**
2046 * mnt_set_expiry - Put a mount on an expiration list
2047 * @mnt: The mount to list.
2048 * @expiry_list: The list to add the mount to.
2049 */
2050void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2051{
2052        namespace_lock();
2053        br_write_lock(&vfsmount_lock);
2054
2055        list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
2056
2057        br_write_unlock(&vfsmount_lock);
2058        namespace_unlock();
2059}
2060EXPORT_SYMBOL(mnt_set_expiry);
2061
2062/*
2063 * process a list of expirable mountpoints with the intent of discarding any
2064 * mountpoints that aren't in use and haven't been touched since last we came
2065 * here
2066 */
2067void mark_mounts_for_expiry(struct list_head *mounts)
2068{
2069        struct mount *mnt, *next;
2070        LIST_HEAD(graveyard);
2071
2072        if (list_empty(mounts))
2073                return;
2074
2075        namespace_lock();
2076        br_write_lock(&vfsmount_lock);
2077
2078        /* extract from the expiration list every vfsmount that matches the
2079         * following criteria:
2080         * - only referenced by its parent vfsmount
2081         * - still marked for expiry (marked on the last call here; marks are
2082         *   cleared by mntput())
2083         */
2084        list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2085                if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2086                        propagate_mount_busy(mnt, 1))
2087                        continue;
2088                list_move(&mnt->mnt_expire, &graveyard);
2089        }
2090        while (!list_empty(&graveyard)) {
2091                mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
2092                touch_mnt_namespace(mnt->mnt_ns);
2093                umount_tree(mnt, 1);
2094        }
2095        br_write_unlock(&vfsmount_lock);
2096        namespace_unlock();
2097}
2098
2099EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2100
2101/*
2102 * Ripoff of 'select_parent()'
2103 *
2104 * search the list of submounts for a given mountpoint, and move any
2105 * shrinkable submounts to the 'graveyard' list.
2106 */
2107static int select_submounts(struct mount *parent, struct list_head *graveyard)
2108{
2109        struct mount *this_parent = parent;
2110        struct list_head *next;
2111        int found = 0;
2112
2113repeat:
2114        next = this_parent->mnt_mounts.next;
2115resume:
2116        while (next != &this_parent->mnt_mounts) {
2117                struct list_head *tmp = next;
2118                struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
2119
2120                next = tmp->next;
2121                if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
2122                        continue;
2123                /*
2124                 * Descend a level if the d_mounts list is non-empty.
2125                 */
2126                if (!list_empty(&mnt->mnt_mounts)) {
2127                        this_parent = mnt;
2128                        goto repeat;
2129                }
2130
2131                if (!propagate_mount_busy(mnt, 1)) {
2132                        list_move_tail(&mnt->mnt_expire, graveyard);
2133                        found++;
2134                }
2135        }
2136        /*
2137         * All done at this level ... ascend and resume the search
2138         */
2139        if (this_parent != parent) {
2140                next = this_parent->mnt_child.next;
2141                this_parent = this_parent->mnt_parent;
2142                goto resume;
2143        }
2144        return found;
2145}
2146
2147/*
2148 * process a list of expirable mountpoints with the intent of discarding any
2149 * submounts of a specific parent mountpoint
2150 *
2151 * vfsmount_lock must be held for write
2152 */
2153static void shrink_submounts(struct mount *mnt)
2154{
2155        LIST_HEAD(graveyard);
2156        struct mount *m;
2157
2158        /* extract submounts of 'mountpoint' from the expiration list */
2159        while (select_submounts(mnt, &graveyard)) {
2160                while (!list_empty(&graveyard)) {
2161                        m = list_first_entry(&graveyard, struct mount,
2162                                                mnt_expire);
2163                        touch_mnt_namespace(m->mnt_ns);
2164                        umount_tree(m, 1);
2165                }
2166        }
2167}
2168
2169/*
2170 * Some copy_from_user() implementations do not return the exact number of
2171 * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
2172 * Note that this function differs from copy_from_user() in that it will oops
2173 * on bad values of `to', rather than returning a short copy.
2174 */
2175static long exact_copy_from_user(void *to, const void __user * from,
2176                                 unsigned long n)
2177{
2178        char *t = to;
2179        const char __user *f = from;
2180        char c;
2181
2182        if (!access_ok(VERIFY_READ, from, n))
2183                return n;
2184
2185        while (n) {
2186                if (__get_user(c, f)) {
2187                        memset(t, 0, n);
2188                        break;
2189                }
2190                *t++ = c;
2191                f++;
2192                n--;
2193        }
2194        return n;
2195}
2196
2197int copy_mount_options(const void __user * data, unsigned long *where)
2198{
2199        int i;
2200        unsigned long page;
2201        unsigned long size;
2202
2203        *where = 0;
2204        if (!data)
2205                return 0;
2206
2207        if (!(page = __get_free_page(GFP_KERNEL)))
2208                return -ENOMEM;
2209
2210        /* We only care that *some* data at the address the user
2211         * gave us is valid.  Just in case, we'll zero
2212         * the remainder of the page.
2213         */
2214        /* copy_from_user cannot cross TASK_SIZE ! */
2215        size = TASK_SIZE - (unsigned long)data;
2216        if (size > PAGE_SIZE)
2217                size = PAGE_SIZE;
2218
2219        i = size - exact_copy_from_user((void *)page, data, size);
2220        if (!i) {
2221                free_page(page);
2222                return -EFAULT;
2223        }
2224        if (i != PAGE_SIZE)
2225                memset((char *)page + i, 0, PAGE_SIZE - i);
2226        *where = page;
2227        return 0;
2228}
2229
2230int copy_mount_string(const void __user *data, char **where)
2231{
2232        char *tmp;
2233
2234        if (!data) {
2235                *where = NULL;
2236                return 0;
2237        }
2238
2239        tmp = strndup_user(data, PAGE_SIZE);
2240        if (IS_ERR(tmp))
2241                return PTR_ERR(tmp);
2242
2243        *where = tmp;
2244        return 0;
2245}
2246
2247/*
2248 * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
2249 * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
2250 *
2251 * data is a (void *) that can point to any structure up to
2252 * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
2253 * information (or be NULL).
2254 *
2255 * Pre-0.97 versions of mount() didn't have a flags word.
2256 * When the flags word was introduced its top half was required
2257 * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
2258 * Therefore, if this magic number is present, it carries no information
2259 * and must be discarded.
2260 */
2261long do_mount(const char *dev_name, const char *dir_name,
2262                const char *type_page, unsigned long flags, void *data_page)
2263{
2264        struct path path;
2265        int retval = 0;
2266        int mnt_flags = 0;
2267
2268        /* Discard magic */
2269        if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
2270                flags &= ~MS_MGC_MSK;
2271
2272        /* Basic sanity checks */
2273
2274        if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
2275                return -EINVAL;
2276
2277        if (data_page)
2278                ((char *)data_page)[PAGE_SIZE - 1] = 0;
2279
2280        /* ... and get the mountpoint */
2281        retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
2282        if (retval)
2283                return retval;
2284
2285        retval = security_sb_mount(dev_name, &path,
2286                                   type_page, flags, data_page);
2287        if (!retval && !may_mount())
2288                retval = -EPERM;
2289        if (retval)
2290                goto dput_out;
2291
2292        /* Default to relatime unless overriden */
2293        if (!(flags & MS_NOATIME))
2294                mnt_flags |= MNT_RELATIME;
2295
2296        /* Separate the per-mountpoint flags */
2297        if (flags & MS_NOSUID)
2298                mnt_flags |= MNT_NOSUID;
2299        if (flags & MS_NODEV)
2300                mnt_flags |= MNT_NODEV;
2301        if (flags & MS_NOEXEC)
2302                mnt_flags |= MNT_NOEXEC;
2303        if (flags & MS_NOATIME)
2304                mnt_flags |= MNT_NOATIME;
2305        if (flags & MS_NODIRATIME)
2306                mnt_flags |= MNT_NODIRATIME;
2307        if (flags & MS_STRICTATIME)
2308                mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
2309        if (flags & MS_RDONLY)
2310                mnt_flags |= MNT_READONLY;
2311
2312        flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
2313                   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
2314                   MS_STRICTATIME);
2315
2316        if (flags & MS_REMOUNT)
2317                retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
2318                                    data_page);
2319        else if (flags & MS_BIND)
2320                retval = do_loopback(&path, dev_name, flags & MS_REC);
2321        else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2322                retval = do_change_type(&path, flags);
2323        else if (flags & MS_MOVE)
2324                retval = do_move_mount(&path, dev_name);
2325        else
2326                retval = do_new_mount(&path, type_page, flags, mnt_flags,
2327                                      dev_name, data_page);
2328dput_out:
2329        path_put(&path);
2330        return retval;
2331}
2332
2333static void free_mnt_ns(struct mnt_namespace *ns)
2334{
2335        proc_free_inum(ns->proc_inum);
2336        put_user_ns(ns->user_ns);
2337        kfree(ns);
2338}
2339
2340/*
2341 * Assign a sequence number so we can detect when we attempt to bind
2342 * mount a reference to an older mount namespace into the current
2343 * mount namespace, preventing reference counting loops.  A 64bit
2344 * number incrementing at 10Ghz will take 12,427 years to wrap which
2345 * is effectively never, so we can ignore the possibility.
2346 */
2347static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
2348
2349static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
2350{
2351        struct mnt_namespace *new_ns;
2352        int ret;
2353
2354        new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
2355        if (!new_ns)
2356                return ERR_PTR(-ENOMEM);
2357        ret = proc_alloc_inum(&new_ns->proc_inum);
2358        if (ret) {
2359                kfree(new_ns);
2360                return ERR_PTR(ret);
2361        }
2362        new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
2363        atomic_set(&new_ns->count, 1);
2364        new_ns->root = NULL;
2365        INIT_LIST_HEAD(&new_ns->list);
2366        init_waitqueue_head(&new_ns->poll);
2367        new_ns->event = 0;
2368        new_ns->user_ns = get_user_ns(user_ns);
2369        return new_ns;
2370}
2371
2372/*
2373 * Allocate a new namespace structure and populate it with contents
2374 * copied from the namespace of the passed in task structure.
2375 */
2376static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
2377                struct user_namespace *user_ns, struct fs_struct *fs)
2378{
2379        struct mnt_namespace *new_ns;
2380        struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
2381        struct mount *p, *q;
2382        struct mount *old = mnt_ns->root;
2383        struct mount *new;
2384        int copy_flags;
2385
2386        new_ns = alloc_mnt_ns(user_ns);
2387        if (IS_ERR(new_ns))
2388                return new_ns;
2389
2390        namespace_lock();
2391        /* First pass: copy the tree topology */
2392        copy_flags = CL_COPY_ALL | CL_EXPIRE;
2393        if (user_ns != mnt_ns->user_ns)
2394                copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
2395        new = copy_tree(old, old->mnt.mnt_root, copy_flags);
2396        if (IS_ERR(new)) {
2397                namespace_unlock();
2398                free_mnt_ns(new_ns);
2399                return ERR_CAST(new);
2400        }
2401        new_ns->root = new;
2402        br_write_lock(&vfsmount_lock);
2403        list_add_tail(&new_ns->list, &new->mnt_list);
2404        br_write_unlock(&vfsmount_lock);
2405
2406        /*
2407         * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
2408         * as belonging to new namespace.  We have already acquired a private
2409         * fs_struct, so tsk->fs->lock is not needed.
2410         */
2411        p = old;
2412        q = new;
2413        while (p) {
2414                q->mnt_ns = new_ns;
2415                if (fs) {
2416                        if (&p->mnt == fs->root.mnt) {
2417                                fs->root.mnt = mntget(&q->mnt);
2418                                rootmnt = &p->mnt;
2419                        }
2420                        if (&p->mnt == fs->pwd.mnt) {
2421                                fs->pwd.mnt = mntget(&q->mnt);
2422                                pwdmnt = &p->mnt;
2423                        }
2424                }
2425                p = next_mnt(p, old);
2426                q = next_mnt(q, new);
2427        }
2428        namespace_unlock();
2429
2430        if (rootmnt)
2431                mntput(rootmnt);
2432        if (pwdmnt)
2433                mntput(pwdmnt);
2434
2435        return new_ns;
2436}
2437
2438struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
2439                struct user_namespace *user_ns, struct fs_struct *new_fs)
2440{
2441        struct mnt_namespace *new_ns;
2442
2443        BUG_ON(!ns);
2444        get_mnt_ns(ns);
2445
2446        if (!(flags & CLONE_NEWNS))
2447                return ns;
2448
2449        new_ns = dup_mnt_ns(ns, user_ns, new_fs);
2450
2451        put_mnt_ns(ns);
2452        return new_ns;
2453}
2454
2455/**
2456 * create_mnt_ns - creates a private namespace and adds a root filesystem
2457 * @mnt: pointer to the new root filesystem mountpoint
2458 */
2459static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
2460{
2461        struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
2462        if (!IS_ERR(new_ns)) {
2463                struct mount *mnt = real_mount(m);
2464                mnt->mnt_ns = new_ns;
2465                new_ns->root = mnt;
2466                list_add(&mnt->mnt_list, &new_ns->list);
2467        } else {
2468                mntput(m);
2469        }
2470        return new_ns;
2471}
2472
2473struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
2474{
2475        struct mnt_namespace *ns;
2476        struct super_block *s;
2477        struct path path;
2478        int err;
2479
2480        ns = create_mnt_ns(mnt);
2481        if (IS_ERR(ns))
2482                return ERR_CAST(ns);
2483
2484        err = vfs_path_lookup(mnt->mnt_root, mnt,
2485                        name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
2486
2487        put_mnt_ns(ns);
2488
2489        if (err)
2490                return ERR_PTR(err);
2491
2492        /* trade a vfsmount reference for active sb one */
2493        s = path.mnt->mnt_sb;
2494        atomic_inc(&s->s_active);
2495        mntput(path.mnt);
2496        /* lock the sucker */
2497        down_write(&s->s_umount);
2498        /* ... and return the root of (sub)tree on it */
2499        return path.dentry;
2500}
2501EXPORT_SYMBOL(mount_subtree);
2502
2503SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
2504                char __user *, type, unsigned long, flags, void __user *, data)
2505{
2506        int ret;
2507        char *kernel_type;
2508        struct filename *kernel_dir;
2509        char *kernel_dev;
2510        unsigned long data_page;
2511
2512        ret = copy_mount_string(type, &kernel_type);
2513        if (ret < 0)
2514                goto out_type;
2515
2516        kernel_dir = getname(dir_name);
2517        if (IS_ERR(kernel_dir)) {
2518                ret = PTR_ERR(kernel_dir);
2519                goto out_dir;
2520        }
2521
2522        ret = copy_mount_string(dev_name, &kernel_dev);
2523        if (ret < 0)
2524                goto out_dev;
2525
2526        ret = copy_mount_options(data, &data_page);
2527        if (ret < 0)
2528                goto out_data;
2529
2530        ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags,
2531                (void *) data_page);
2532
2533        free_page(data_page);
2534out_data:
2535        kfree(kernel_dev);
2536out_dev:
2537        putname(kernel_dir);
2538out_dir:
2539        kfree(kernel_type);
2540out_type:
2541        return ret;
2542}
2543
2544/*
2545 * Return true if path is reachable from root
2546 *
2547 * namespace_sem or vfsmount_lock is held
2548 */
2549bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
2550                         const struct path *root)
2551{
2552        while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
2553                dentry = mnt->mnt_mountpoint;
2554                mnt = mnt->mnt_parent;
2555        }
2556        return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
2557}
2558
2559int path_is_under(struct path *path1, struct path *path2)
2560{
2561        int res;
2562        br_read_lock(&vfsmount_lock);
2563        res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
2564        br_read_unlock(&vfsmount_lock);
2565        return res;
2566}
2567EXPORT_SYMBOL(path_is_under);
2568
2569/*
2570 * pivot_root Semantics:
2571 * Moves the root file system of the current process to the directory put_old,
2572 * makes new_root as the new root file system of the current process, and sets
2573 * root/cwd of all processes which had them on the current root to new_root.
2574 *
2575 * Restrictions:
2576 * The new_root and put_old must be directories, and  must not be on the
2577 * same file  system as the current process root. The put_old  must  be
2578 * underneath new_root,  i.e. adding a non-zero number of /.. to the string
2579 * pointed to by put_old must yield the same directory as new_root. No other
2580 * file system may be mounted on put_old. After all, new_root is a mountpoint.
2581 *
2582 * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
2583 * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
2584 * in this situation.
2585 *
2586 * Notes:
2587 *  - we don't move root/cwd if they are not at the root (reason: if something
2588 *    cared enough to change them, it's probably wrong to force them elsewhere)
2589 *  - it's okay to pick a root that isn't the root of a file system, e.g.
2590 *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
2591 *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
2592 *    first.
2593 */
2594SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
2595                const char __user *, put_old)
2596{
2597        struct path new, old, parent_path, root_parent, root;
2598        struct mount *new_mnt, *root_mnt, *old_mnt;
2599        struct mountpoint *old_mp, *root_mp;
2600        int error;
2601
2602        if (!may_mount())
2603                return -EPERM;
2604
2605        error = user_path_dir(new_root, &new);
2606        if (error)
2607                goto out0;
2608
2609        error = user_path_dir(put_old, &old);
2610        if (error)
2611                goto out1;
2612
2613        error = security_sb_pivotroot(&old, &new);
2614        if (error)
2615                goto out2;
2616
2617        get_fs_root(current->fs, &root);
2618        old_mp = lock_mount(&old);
2619        error = PTR_ERR(old_mp);
2620        if (IS_ERR(old_mp))
2621                goto out3;
2622
2623        error = -EINVAL;
2624        new_mnt = real_mount(new.mnt);
2625        root_mnt = real_mount(root.mnt);
2626        old_mnt = real_mount(old.mnt);
2627        if (IS_MNT_SHARED(old_mnt) ||
2628                IS_MNT_SHARED(new_mnt->mnt_parent) ||
2629                IS_MNT_SHARED(root_mnt->mnt_parent))
2630                goto out4;
2631        if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
2632                goto out4;
2633        error = -ENOENT;
2634        if (d_unlinked(new.dentry))
2635                goto out4;
2636        error = -EBUSY;
2637        if (new_mnt == root_mnt || old_mnt == root_mnt)
2638                goto out4; /* loop, on the same file system  */
2639        error = -EINVAL;
2640        if (root.mnt->mnt_root != root.dentry)
2641                goto out4; /* not a mountpoint */
2642        if (!mnt_has_parent(root_mnt))
2643                goto out4; /* not attached */
2644        root_mp = root_mnt->mnt_mp;
2645        if (new.mnt->mnt_root != new.dentry)
2646                goto out4; /* not a mountpoint */
2647        if (!mnt_has_parent(new_mnt))
2648                goto out4; /* not attached */
2649        /* make sure we can reach put_old from new_root */
2650        if (!is_path_reachable(old_mnt, old.dentry, &new))
2651                goto out4;
2652        root_mp->m_count++; /* pin it so it won't go away */
2653        br_write_lock(&vfsmount_lock);
2654        detach_mnt(new_mnt, &parent_path);
2655        detach_mnt(root_mnt, &root_parent);
2656        /* mount old root on put_old */
2657        attach_mnt(root_mnt, old_mnt, old_mp);
2658        /* mount new_root on / */
2659        attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
2660        touch_mnt_namespace(current->nsproxy->mnt_ns);
2661        br_write_unlock(&vfsmount_lock);
2662        chroot_fs_refs(&root, &new);
2663        put_mountpoint(root_mp);
2664        error = 0;
2665out4:
2666        unlock_mount(old_mp);
2667        if (!error) {
2668                path_put(&root_parent);
2669                path_put(&parent_path);
2670        }
2671out3:
2672        path_put(&root);
2673out2:
2674        path_put(&old);
2675out1:
2676        path_put(&new);
2677out0:
2678        return error;
2679}
2680
2681static void __init init_mount_tree(void)
2682{
2683        struct vfsmount *mnt;
2684        struct mnt_namespace *ns;
2685        struct path root;
2686        struct file_system_type *type;
2687
2688        type = get_fs_type("rootfs");
2689        if (!type)
2690                panic("Can't find rootfs type");
2691        mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
2692        put_filesystem(type);
2693        if (IS_ERR(mnt))
2694                panic("Can't create rootfs");
2695
2696        ns = create_mnt_ns(mnt);
2697        if (IS_ERR(ns))
2698                panic("Can't allocate initial namespace");
2699
2700        init_task.nsproxy->mnt_ns = ns;
2701        get_mnt_ns(ns);
2702
2703        root.mnt = mnt;
2704        root.dentry = mnt->mnt_root;
2705
2706        set_fs_pwd(current->fs, &root);
2707        set_fs_root(current->fs, &root);
2708}
2709
2710void __init mnt_init(void)
2711{
2712        unsigned u;
2713        int err;
2714
2715        init_rwsem(&namespace_sem);
2716
2717        mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
2718                        0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2719
2720        mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
2721        mountpoint_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
2722
2723        if (!mount_hashtable || !mountpoint_hashtable)
2724                panic("Failed to allocate mount hash table\n");
2725
2726        printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
2727
2728        for (u = 0; u < HASH_SIZE; u++)
2729                INIT_LIST_HEAD(&mount_hashtable[u]);
2730        for (u = 0; u < HASH_SIZE; u++)
2731                INIT_LIST_HEAD(&mountpoint_hashtable[u]);
2732
2733        br_lock_init(&vfsmount_lock);
2734
2735        err = sysfs_init();
2736        if (err)
2737                printk(KERN_WARNING "%s: sysfs_init error: %d\n",
2738                        __func__, err);
2739        fs_kobj = kobject_create_and_add("fs", NULL);
2740        if (!fs_kobj)
2741                printk(KERN_WARNING "%s: kobj create error\n", __func__);
2742        init_rootfs();
2743        init_mount_tree();
2744}
2745
2746void put_mnt_ns(struct mnt_namespace *ns)
2747{
2748        if (!atomic_dec_and_test(&ns->count))
2749                return;
2750        namespace_lock();
2751        br_write_lock(&vfsmount_lock);
2752        umount_tree(ns->root, 0);
2753        br_write_unlock(&vfsmount_lock);
2754        namespace_unlock();
2755        free_mnt_ns(ns);
2756}
2757
2758struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
2759{
2760        struct vfsmount *mnt;
2761        mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
2762        if (!IS_ERR(mnt)) {
2763                /*
2764                 * it is a longterm mount, don't release mnt until
2765                 * we unmount before file sys is unregistered
2766                */
2767                real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
2768        }
2769        return mnt;
2770}
2771EXPORT_SYMBOL_GPL(kern_mount_data);
2772
2773void kern_unmount(struct vfsmount *mnt)
2774{
2775        /* release long term mount so mount point can be released */
2776        if (!IS_ERR_OR_NULL(mnt)) {
2777                br_write_lock(&vfsmount_lock);
2778                real_mount(mnt)->mnt_ns = NULL;
2779                br_write_unlock(&vfsmount_lock);
2780                mntput(mnt);
2781        }
2782}
2783EXPORT_SYMBOL(kern_unmount);
2784
2785bool our_mnt(struct vfsmount *mnt)
2786{
2787        return check_mnt(real_mount(mnt));
2788}
2789
2790bool current_chrooted(void)
2791{
2792        /* Does the current process have a non-standard root */
2793        struct path ns_root;
2794        struct path fs_root;
2795        bool chrooted;
2796
2797        /* Find the namespace root */
2798        ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
2799        ns_root.dentry = ns_root.mnt->mnt_root;
2800        path_get(&ns_root);
2801        while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
2802                ;
2803
2804        get_fs_root(current->fs, &fs_root);
2805
2806        chrooted = !path_equal(&fs_root, &ns_root);
2807
2808        path_put(&fs_root);
2809        path_put(&ns_root);
2810
2811        return chrooted;
2812}
2813
2814void update_mnt_policy(struct user_namespace *userns)
2815{
2816        struct mnt_namespace *ns = current->nsproxy->mnt_ns;
2817        struct mount *mnt;
2818
2819        down_read(&namespace_sem);
2820        list_for_each_entry(mnt, &ns->list, mnt_list) {
2821                switch (mnt->mnt.mnt_sb->s_magic) {
2822                case SYSFS_MAGIC:
2823                        userns->may_mount_sysfs = true;
2824                        break;
2825                case PROC_SUPER_MAGIC:
2826                        userns->may_mount_proc = true;
2827                        break;
2828                }
2829                if (userns->may_mount_sysfs && userns->may_mount_proc)
2830                        break;
2831        }
2832        up_read(&namespace_sem);
2833}
2834
2835static void *mntns_get(struct task_struct *task)
2836{
2837        struct mnt_namespace *ns = NULL;
2838        struct nsproxy *nsproxy;
2839
2840        rcu_read_lock();
2841        nsproxy = task_nsproxy(task);
2842        if (nsproxy) {
2843                ns = nsproxy->mnt_ns;
2844                get_mnt_ns(ns);
2845        }
2846        rcu_read_unlock();
2847
2848        return ns;
2849}
2850
2851static void mntns_put(void *ns)
2852{
2853        put_mnt_ns(ns);
2854}
2855
2856static int mntns_install(struct nsproxy *nsproxy, void *ns)
2857{
2858        struct fs_struct *fs = current->fs;
2859        struct mnt_namespace *mnt_ns = ns;
2860        struct path root;
2861
2862        if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
2863            !nsown_capable(CAP_SYS_CHROOT) ||
2864            !nsown_capable(CAP_SYS_ADMIN))
2865                return -EPERM;
2866
2867        if (fs->users != 1)
2868                return -EINVAL;
2869
2870        get_mnt_ns(mnt_ns);
2871        put_mnt_ns(nsproxy->mnt_ns);
2872        nsproxy->mnt_ns = mnt_ns;
2873
2874        /* Find the root */
2875        root.mnt    = &mnt_ns->root->mnt;
2876        root.dentry = mnt_ns->root->mnt.mnt_root;
2877        path_get(&root);
2878        while(d_mountpoint(root.dentry) && follow_down_one(&root))
2879                ;
2880
2881        /* Update the pwd and root */
2882        set_fs_pwd(fs, &root);
2883        set_fs_root(fs, &root);
2884
2885        path_put(&root);
2886        return 0;
2887}
2888
2889static unsigned int mntns_inum(void *ns)
2890{
2891        struct mnt_namespace *mnt_ns = ns;
2892        return mnt_ns->proc_inum;
2893}
2894
2895const struct proc_ns_operations mntns_operations = {
2896        .name           = "mnt",
2897        .type           = CLONE_NEWNS,
2898        .get            = mntns_get,
2899        .put            = mntns_put,
2900        .install        = mntns_install,
2901        .inum           = mntns_inum,
2902};
2903
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