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/slab.h>
  13#include <linux/sched.h>
  14#include <linux/spinlock.h>
  15#include <linux/percpu.h>
  16#include <linux/init.h>
  17#include <linux/kernel.h>
  18#include <linux/acct.h>
  19#include <linux/capability.h>
  20#include <linux/cpumask.h>
  21#include <linux/module.h>
  22#include <linux/sysfs.h>
  23#include <linux/seq_file.h>
  24#include <linux/mnt_namespace.h>
  25#include <linux/namei.h>
  26#include <linux/nsproxy.h>
  27#include <linux/security.h>
  28#include <linux/mount.h>
  29#include <linux/ramfs.h>
  30#include <linux/log2.h>
  31#include <linux/idr.h>
  32#include <linux/fs_struct.h>
  33#include <linux/fsnotify.h>
  34#include <asm/uaccess.h>
  35#include <asm/unistd.h>
  36#include "pnode.h"
  37#include "internal.h"
  38
  39#define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
  40#define HASH_SIZE (1UL << HASH_SHIFT)
  41
  42static int event;
  43static DEFINE_IDA(mnt_id_ida);
  44static DEFINE_IDA(mnt_group_ida);
  45static DEFINE_SPINLOCK(mnt_id_lock);
  46static int mnt_id_start = 0;
  47static int mnt_group_start = 1;
  48
  49static struct list_head *mount_hashtable __read_mostly;
  50static struct kmem_cache *mnt_cache __read_mostly;
  51static struct rw_semaphore namespace_sem;
  52
  53/* /sys/fs */
  54struct kobject *fs_kobj;
  55EXPORT_SYMBOL_GPL(fs_kobj);
  56
  57/*
  58 * vfsmount lock may be taken for read to prevent changes to the
  59 * vfsmount hash, ie. during mountpoint lookups or walking back
  60 * up the tree.
  61 *
  62 * It should be taken for write in all cases where the vfsmount
  63 * tree or hash is modified or when a vfsmount structure is modified.
  64 */
  65DEFINE_BRLOCK(vfsmount_lock);
  66
  67static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
  68{
  69        unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
  70        tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
  71        tmp = tmp + (tmp >> HASH_SHIFT);
  72        return tmp & (HASH_SIZE - 1);
  73}
  74
  75#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
  76
  77/*
  78 * allocation is serialized by namespace_sem, but we need the spinlock to
  79 * serialize with freeing.
  80 */
  81static int mnt_alloc_id(struct vfsmount *mnt)
  82{
  83        int res;
  84
  85retry:
  86        ida_pre_get(&mnt_id_ida, GFP_KERNEL);
  87        spin_lock(&mnt_id_lock);
  88        res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
  89        if (!res)
  90                mnt_id_start = mnt->mnt_id + 1;
  91        spin_unlock(&mnt_id_lock);
  92        if (res == -EAGAIN)
  93                goto retry;
  94
  95        return res;
  96}
  97
  98static void mnt_free_id(struct vfsmount *mnt)
  99{
 100        int id = mnt->mnt_id;
 101        spin_lock(&mnt_id_lock);
 102        ida_remove(&mnt_id_ida, id);
 103        if (mnt_id_start > id)
 104                mnt_id_start = id;
 105        spin_unlock(&mnt_id_lock);
 106}
 107
 108/*
 109 * Allocate a new peer group ID
 110 *
 111 * mnt_group_ida is protected by namespace_sem
 112 */
 113static int mnt_alloc_group_id(struct vfsmount *mnt)
 114{
 115        int res;
 116
 117        if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
 118                return -ENOMEM;
 119
 120        res = ida_get_new_above(&mnt_group_ida,
 121                                mnt_group_start,
 122                                &mnt->mnt_group_id);
 123        if (!res)
 124                mnt_group_start = mnt->mnt_group_id + 1;
 125
 126        return res;
 127}
 128
 129/*
 130 * Release a peer group ID
 131 */
 132void mnt_release_group_id(struct vfsmount *mnt)
 133{
 134        int id = mnt->mnt_group_id;
 135        ida_remove(&mnt_group_ida, id);
 136        if (mnt_group_start > id)
 137                mnt_group_start = id;
 138        mnt->mnt_group_id = 0;
 139}
 140
 141/*
 142 * vfsmount lock must be held for read
 143 */
 144static inline void mnt_add_count(struct vfsmount *mnt, int n)
 145{
 146#ifdef CONFIG_SMP
 147        this_cpu_add(mnt->mnt_pcp->mnt_count, n);
 148#else
 149        preempt_disable();
 150        mnt->mnt_count += n;
 151        preempt_enable();
 152#endif
 153}
 154
 155static inline void mnt_set_count(struct vfsmount *mnt, int n)
 156{
 157#ifdef CONFIG_SMP
 158        this_cpu_write(mnt->mnt_pcp->mnt_count, n);
 159#else
 160        mnt->mnt_count = n;
 161#endif
 162}
 163
 164/*
 165 * vfsmount lock must be held for read
 166 */
 167static inline void mnt_inc_count(struct vfsmount *mnt)
 168{
 169        mnt_add_count(mnt, 1);
 170}
 171
 172/*
 173 * vfsmount lock must be held for read
 174 */
 175static inline void mnt_dec_count(struct vfsmount *mnt)
 176{
 177        mnt_add_count(mnt, -1);
 178}
 179
 180/*
 181 * vfsmount lock must be held for write
 182 */
 183unsigned int mnt_get_count(struct vfsmount *mnt)
 184{
 185#ifdef CONFIG_SMP
 186        unsigned int count = 0;
 187        int cpu;
 188
 189        for_each_possible_cpu(cpu) {
 190                count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
 191        }
 192
 193        return count;
 194#else
 195        return mnt->mnt_count;
 196#endif
 197}
 198
 199static struct vfsmount *alloc_vfsmnt(const char *name)
 200{
 201        struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
 202        if (mnt) {
 203                int err;
 204
 205                err = mnt_alloc_id(mnt);
 206                if (err)
 207                        goto out_free_cache;
 208
 209                if (name) {
 210                        mnt->mnt_devname = kstrdup(name, GFP_KERNEL);
 211                        if (!mnt->mnt_devname)
 212                                goto out_free_id;
 213                }
 214
 215#ifdef CONFIG_SMP
 216                mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
 217                if (!mnt->mnt_pcp)
 218                        goto out_free_devname;
 219
 220                this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
 221#else
 222                mnt->mnt_count = 1;
 223                mnt->mnt_writers = 0;
 224#endif
 225
 226                INIT_LIST_HEAD(&mnt->mnt_hash);
 227                INIT_LIST_HEAD(&mnt->mnt_child);
 228                INIT_LIST_HEAD(&mnt->mnt_mounts);
 229                INIT_LIST_HEAD(&mnt->mnt_list);
 230                INIT_LIST_HEAD(&mnt->mnt_expire);
 231                INIT_LIST_HEAD(&mnt->mnt_share);
 232                INIT_LIST_HEAD(&mnt->mnt_slave_list);
 233                INIT_LIST_HEAD(&mnt->mnt_slave);
 234#ifdef CONFIG_FSNOTIFY
 235                INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
 236#endif
 237        }
 238        return mnt;
 239
 240#ifdef CONFIG_SMP
 241out_free_devname:
 242        kfree(mnt->mnt_devname);
 243#endif
 244out_free_id:
 245        mnt_free_id(mnt);
 246out_free_cache:
 247        kmem_cache_free(mnt_cache, mnt);
 248        return NULL;
 249}
 250
 251/*
 252 * Most r/o checks on a fs are for operations that take
 253 * discrete amounts of time, like a write() or unlink().
 254 * We must keep track of when those operations start
 255 * (for permission checks) and when they end, so that
 256 * we can determine when writes are able to occur to
 257 * a filesystem.
 258 */
 259/*
 260 * __mnt_is_readonly: check whether a mount is read-only
 261 * @mnt: the mount to check for its write status
 262 *
 263 * This shouldn't be used directly ouside of the VFS.
 264 * It does not guarantee that the filesystem will stay
 265 * r/w, just that it is right *now*.  This can not and
 266 * should not be used in place of IS_RDONLY(inode).
 267 * mnt_want/drop_write() will _keep_ the filesystem
 268 * r/w.
 269 */
 270int __mnt_is_readonly(struct vfsmount *mnt)
 271{
 272        if (mnt->mnt_flags & MNT_READONLY)
 273                return 1;
 274        if (mnt->mnt_sb->s_flags & MS_RDONLY)
 275                return 1;
 276        return 0;
 277}
 278EXPORT_SYMBOL_GPL(__mnt_is_readonly);
 279
 280static inline void mnt_inc_writers(struct vfsmount *mnt)
 281{
 282#ifdef CONFIG_SMP
 283        this_cpu_inc(mnt->mnt_pcp->mnt_writers);
 284#else
 285        mnt->mnt_writers++;
 286#endif
 287}
 288
 289static inline void mnt_dec_writers(struct vfsmount *mnt)
 290{
 291#ifdef CONFIG_SMP
 292        this_cpu_dec(mnt->mnt_pcp->mnt_writers);
 293#else
 294        mnt->mnt_writers--;
 295#endif
 296}
 297
 298static unsigned int mnt_get_writers(struct vfsmount *mnt)
 299{
 300#ifdef CONFIG_SMP
 301        unsigned int count = 0;
 302        int cpu;
 303
 304        for_each_possible_cpu(cpu) {
 305                count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
 306        }
 307
 308        return count;
 309#else
 310        return mnt->mnt_writers;
 311#endif
 312}
 313
 314/*
 315 * Most r/o checks on a fs are for operations that take
 316 * discrete amounts of time, like a write() or unlink().
 317 * We must keep track of when those operations start
 318 * (for permission checks) and when they end, so that
 319 * we can determine when writes are able to occur to
 320 * a filesystem.
 321 */
 322/**
 323 * mnt_want_write - get write access to a mount
 324 * @mnt: the mount on which to take a write
 325 *
 326 * This tells the low-level filesystem that a write is
 327 * about to be performed to it, and makes sure that
 328 * writes are allowed before returning success.  When
 329 * the write operation is finished, mnt_drop_write()
 330 * must be called.  This is effectively a refcount.
 331 */
 332int mnt_want_write(struct vfsmount *mnt)
 333{
 334        int ret = 0;
 335
 336        preempt_disable();
 337        mnt_inc_writers(mnt);
 338        /*
 339         * The store to mnt_inc_writers must be visible before we pass
 340         * MNT_WRITE_HOLD loop below, so that the slowpath can see our
 341         * incremented count after it has set MNT_WRITE_HOLD.
 342         */
 343        smp_mb();
 344        while (mnt->mnt_flags & MNT_WRITE_HOLD)
 345                cpu_relax();
 346        /*
 347         * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
 348         * be set to match its requirements. So we must not load that until
 349         * MNT_WRITE_HOLD is cleared.
 350         */
 351        smp_rmb();
 352        if (__mnt_is_readonly(mnt)) {
 353                mnt_dec_writers(mnt);
 354                ret = -EROFS;
 355                goto out;
 356        }
 357out:
 358        preempt_enable();
 359        return ret;
 360}
 361EXPORT_SYMBOL_GPL(mnt_want_write);
 362
 363/**
 364 * mnt_clone_write - get write access to a mount
 365 * @mnt: the mount on which to take a write
 366 *
 367 * This is effectively like mnt_want_write, except
 368 * it must only be used to take an extra write reference
 369 * on a mountpoint that we already know has a write reference
 370 * on it. This allows some optimisation.
 371 *
 372 * After finished, mnt_drop_write must be called as usual to
 373 * drop the reference.
 374 */
 375int mnt_clone_write(struct vfsmount *mnt)
 376{
 377        /* superblock may be r/o */
 378        if (__mnt_is_readonly(mnt))
 379                return -EROFS;
 380        preempt_disable();
 381        mnt_inc_writers(mnt);
 382        preempt_enable();
 383        return 0;
 384}
 385EXPORT_SYMBOL_GPL(mnt_clone_write);
 386
 387/**
 388 * mnt_want_write_file - get write access to a file's mount
 389 * @file: the file who's mount on which to take a write
 390 *
 391 * This is like mnt_want_write, but it takes a file and can
 392 * do some optimisations if the file is open for write already
 393 */
 394int mnt_want_write_file(struct file *file)
 395{
 396        struct inode *inode = file->f_dentry->d_inode;
 397        if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
 398                return mnt_want_write(file->f_path.mnt);
 399        else
 400                return mnt_clone_write(file->f_path.mnt);
 401}
 402EXPORT_SYMBOL_GPL(mnt_want_write_file);
 403
 404/**
 405 * mnt_drop_write - give up write access to a mount
 406 * @mnt: the mount on which to give up write access
 407 *
 408 * Tells the low-level filesystem that we are done
 409 * performing writes to it.  Must be matched with
 410 * mnt_want_write() call above.
 411 */
 412void mnt_drop_write(struct vfsmount *mnt)
 413{
 414        preempt_disable();
 415        mnt_dec_writers(mnt);
 416        preempt_enable();
 417}
 418EXPORT_SYMBOL_GPL(mnt_drop_write);
 419
 420static int mnt_make_readonly(struct vfsmount *mnt)
 421{
 422        int ret = 0;
 423
 424        br_write_lock(vfsmount_lock);
 425        mnt->mnt_flags |= MNT_WRITE_HOLD;
 426        /*
 427         * After storing MNT_WRITE_HOLD, we'll read the counters. This store
 428         * should be visible before we do.
 429         */
 430        smp_mb();
 431
 432        /*
 433         * With writers on hold, if this value is zero, then there are
 434         * definitely no active writers (although held writers may subsequently
 435         * increment the count, they'll have to wait, and decrement it after
 436         * seeing MNT_READONLY).
 437         *
 438         * It is OK to have counter incremented on one CPU and decremented on
 439         * another: the sum will add up correctly. The danger would be when we
 440         * sum up each counter, if we read a counter before it is incremented,
 441         * but then read another CPU's count which it has been subsequently
 442         * decremented from -- we would see more decrements than we should.
 443         * MNT_WRITE_HOLD protects against this scenario, because
 444         * mnt_want_write first increments count, then smp_mb, then spins on
 445         * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
 446         * we're counting up here.
 447         */
 448        if (mnt_get_writers(mnt) > 0)
 449                ret = -EBUSY;
 450        else
 451                mnt->mnt_flags |= MNT_READONLY;
 452        /*
 453         * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
 454         * that become unheld will see MNT_READONLY.
 455         */
 456        smp_wmb();
 457        mnt->mnt_flags &= ~MNT_WRITE_HOLD;
 458        br_write_unlock(vfsmount_lock);
 459        return ret;
 460}
 461
 462static void __mnt_unmake_readonly(struct vfsmount *mnt)
 463{
 464        br_write_lock(vfsmount_lock);
 465        mnt->mnt_flags &= ~MNT_READONLY;
 466        br_write_unlock(vfsmount_lock);
 467}
 468
 469static void free_vfsmnt(struct vfsmount *mnt)
 470{
 471        kfree(mnt->mnt_devname);
 472        mnt_free_id(mnt);
 473#ifdef CONFIG_SMP
 474        free_percpu(mnt->mnt_pcp);
 475#endif
 476        kmem_cache_free(mnt_cache, mnt);
 477}
 478
 479/*
 480 * find the first or last mount at @dentry on vfsmount @mnt depending on
 481 * @dir. If @dir is set return the first mount else return the last mount.
 482 * vfsmount_lock must be held for read or write.
 483 */
 484struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
 485                              int dir)
 486{
 487        struct list_head *head = mount_hashtable + hash(mnt, dentry);
 488        struct list_head *tmp = head;
 489        struct vfsmount *p, *found = NULL;
 490
 491        for (;;) {
 492                tmp = dir ? tmp->next : tmp->prev;
 493                p = NULL;
 494                if (tmp == head)
 495                        break;
 496                p = list_entry(tmp, struct vfsmount, mnt_hash);
 497                if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
 498                        found = p;
 499                        break;
 500                }
 501        }
 502        return found;
 503}
 504
 505/*
 506 * lookup_mnt increments the ref count before returning
 507 * the vfsmount struct.
 508 */
 509struct vfsmount *lookup_mnt(struct path *path)
 510{
 511        struct vfsmount *child_mnt;
 512
 513        br_read_lock(vfsmount_lock);
 514        if ((child_mnt = __lookup_mnt(path->mnt, path->dentry, 1)))
 515                mntget(child_mnt);
 516        br_read_unlock(vfsmount_lock);
 517        return child_mnt;
 518}
 519
 520static inline int check_mnt(struct vfsmount *mnt)
 521{
 522        return mnt->mnt_ns == current->nsproxy->mnt_ns;
 523}
 524
 525/*
 526 * vfsmount lock must be held for write
 527 */
 528static void touch_mnt_namespace(struct mnt_namespace *ns)
 529{
 530        if (ns) {
 531                ns->event = ++event;
 532                wake_up_interruptible(&ns->poll);
 533        }
 534}
 535
 536/*
 537 * vfsmount lock must be held for write
 538 */
 539static void __touch_mnt_namespace(struct mnt_namespace *ns)
 540{
 541        if (ns && ns->event != event) {
 542                ns->event = event;
 543                wake_up_interruptible(&ns->poll);
 544        }
 545}
 546
 547/*
 548 * Clear dentry's mounted state if it has no remaining mounts.
 549 * vfsmount_lock must be held for write.
 550 */
 551static void dentry_reset_mounted(struct vfsmount *mnt, struct dentry *dentry)
 552{
 553        unsigned u;
 554
 555        for (u = 0; u < HASH_SIZE; u++) {
 556                struct vfsmount *p;
 557
 558                list_for_each_entry(p, &mount_hashtable[u], mnt_hash) {
 559                        if (p->mnt_mountpoint == dentry)
 560                                return;
 561                }
 562        }
 563        spin_lock(&dentry->d_lock);
 564        dentry->d_flags &= ~DCACHE_MOUNTED;
 565        spin_unlock(&dentry->d_lock);
 566}
 567
 568/*
 569 * vfsmount lock must be held for write
 570 */
 571static void detach_mnt(struct vfsmount *mnt, struct path *old_path)
 572{
 573        old_path->dentry = mnt->mnt_mountpoint;
 574        old_path->mnt = mnt->mnt_parent;
 575        mnt->mnt_parent = mnt;
 576        mnt->mnt_mountpoint = mnt->mnt_root;
 577        list_del_init(&mnt->mnt_child);
 578        list_del_init(&mnt->mnt_hash);
 579        dentry_reset_mounted(old_path->mnt, old_path->dentry);
 580}
 581
 582/*
 583 * vfsmount lock must be held for write
 584 */
 585void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
 586                        struct vfsmount *child_mnt)
 587{
 588        child_mnt->mnt_parent = mntget(mnt);
 589        child_mnt->mnt_mountpoint = dget(dentry);
 590        spin_lock(&dentry->d_lock);
 591        dentry->d_flags |= DCACHE_MOUNTED;
 592        spin_unlock(&dentry->d_lock);
 593}
 594
 595/*
 596 * vfsmount lock must be held for write
 597 */
 598static void attach_mnt(struct vfsmount *mnt, struct path *path)
 599{
 600        mnt_set_mountpoint(path->mnt, path->dentry, mnt);
 601        list_add_tail(&mnt->mnt_hash, mount_hashtable +
 602                        hash(path->mnt, path->dentry));
 603        list_add_tail(&mnt->mnt_child, &path->mnt->mnt_mounts);
 604}
 605
 606static inline void __mnt_make_longterm(struct vfsmount *mnt)
 607{
 608#ifdef CONFIG_SMP
 609        atomic_inc(&mnt->mnt_longterm);
 610#endif
 611}
 612
 613/* needs vfsmount lock for write */
 614static inline void __mnt_make_shortterm(struct vfsmount *mnt)
 615{
 616#ifdef CONFIG_SMP
 617        atomic_dec(&mnt->mnt_longterm);
 618#endif
 619}
 620
 621/*
 622 * vfsmount lock must be held for write
 623 */
 624static void commit_tree(struct vfsmount *mnt)
 625{
 626        struct vfsmount *parent = mnt->mnt_parent;
 627        struct vfsmount *m;
 628        LIST_HEAD(head);
 629        struct mnt_namespace *n = parent->mnt_ns;
 630
 631        BUG_ON(parent == mnt);
 632
 633        list_add_tail(&head, &mnt->mnt_list);
 634        list_for_each_entry(m, &head, mnt_list) {
 635                m->mnt_ns = n;
 636                __mnt_make_longterm(m);
 637        }
 638
 639        list_splice(&head, n->list.prev);
 640
 641        list_add_tail(&mnt->mnt_hash, mount_hashtable +
 642                                hash(parent, mnt->mnt_mountpoint));
 643        list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 644        touch_mnt_namespace(n);
 645}
 646
 647static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
 648{
 649        struct list_head *next = p->mnt_mounts.next;
 650        if (next == &p->mnt_mounts) {
 651                while (1) {
 652                        if (p == root)
 653                                return NULL;
 654                        next = p->mnt_child.next;
 655                        if (next != &p->mnt_parent->mnt_mounts)
 656                                break;
 657                        p = p->mnt_parent;
 658                }
 659        }
 660        return list_entry(next, struct vfsmount, mnt_child);
 661}
 662
 663static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
 664{
 665        struct list_head *prev = p->mnt_mounts.prev;
 666        while (prev != &p->mnt_mounts) {
 667                p = list_entry(prev, struct vfsmount, mnt_child);
 668                prev = p->mnt_mounts.prev;
 669        }
 670        return p;
 671}
 672
 673struct vfsmount *
 674vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
 675{
 676        struct vfsmount *mnt;
 677        struct dentry *root;
 678
 679        if (!type)
 680                return ERR_PTR(-ENODEV);
 681
 682        mnt = alloc_vfsmnt(name);
 683        if (!mnt)
 684                return ERR_PTR(-ENOMEM);
 685
 686        if (flags & MS_KERNMOUNT)
 687                mnt->mnt_flags = MNT_INTERNAL;
 688
 689        root = mount_fs(type, flags, name, data);
 690        if (IS_ERR(root)) {
 691                free_vfsmnt(mnt);
 692                return ERR_CAST(root);
 693        }
 694
 695        mnt->mnt_root = root;
 696        mnt->mnt_sb = root->d_sb;
 697        mnt->mnt_mountpoint = mnt->mnt_root;
 698        mnt->mnt_parent = mnt;
 699        return mnt;
 700}
 701EXPORT_SYMBOL_GPL(vfs_kern_mount);
 702
 703static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
 704                                        int flag)
 705{
 706        struct super_block *sb = old->mnt_sb;
 707        struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
 708
 709        if (mnt) {
 710                if (flag & (CL_SLAVE | CL_PRIVATE))
 711                        mnt->mnt_group_id = 0; /* not a peer of original */
 712                else
 713                        mnt->mnt_group_id = old->mnt_group_id;
 714
 715                if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
 716                        int err = mnt_alloc_group_id(mnt);
 717                        if (err)
 718                                goto out_free;
 719                }
 720
 721                mnt->mnt_flags = old->mnt_flags & ~MNT_WRITE_HOLD;
 722                atomic_inc(&sb->s_active);
 723                mnt->mnt_sb = sb;
 724                mnt->mnt_root = dget(root);
 725                mnt->mnt_mountpoint = mnt->mnt_root;
 726                mnt->mnt_parent = mnt;
 727
 728                if (flag & CL_SLAVE) {
 729                        list_add(&mnt->mnt_slave, &old->mnt_slave_list);
 730                        mnt->mnt_master = old;
 731                        CLEAR_MNT_SHARED(mnt);
 732                } else if (!(flag & CL_PRIVATE)) {
 733                        if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
 734                                list_add(&mnt->mnt_share, &old->mnt_share);
 735                        if (IS_MNT_SLAVE(old))
 736                                list_add(&mnt->mnt_slave, &old->mnt_slave);
 737                        mnt->mnt_master = old->mnt_master;
 738                }
 739                if (flag & CL_MAKE_SHARED)
 740                        set_mnt_shared(mnt);
 741
 742                /* stick the duplicate mount on the same expiry list
 743                 * as the original if that was on one */
 744                if (flag & CL_EXPIRE) {
 745                        if (!list_empty(&old->mnt_expire))
 746                                list_add(&mnt->mnt_expire, &old->mnt_expire);
 747                }
 748        }
 749        return mnt;
 750
 751 out_free:
 752        free_vfsmnt(mnt);
 753        return NULL;
 754}
 755
 756static inline void mntfree(struct vfsmount *mnt)
 757{
 758        struct super_block *sb = mnt->mnt_sb;
 759
 760        /*
 761         * This probably indicates that somebody messed
 762         * up a mnt_want/drop_write() pair.  If this
 763         * happens, the filesystem was probably unable
 764         * to make r/w->r/o transitions.
 765         */
 766        /*
 767         * The locking used to deal with mnt_count decrement provides barriers,
 768         * so mnt_get_writers() below is safe.
 769         */
 770        WARN_ON(mnt_get_writers(mnt));
 771        fsnotify_vfsmount_delete(mnt);
 772        dput(mnt->mnt_root);
 773        free_vfsmnt(mnt);
 774        deactivate_super(sb);
 775}
 776
 777static void mntput_no_expire(struct vfsmount *mnt)
 778{
 779put_again:
 780#ifdef CONFIG_SMP
 781        br_read_lock(vfsmount_lock);
 782        if (likely(atomic_read(&mnt->mnt_longterm))) {
 783                mnt_dec_count(mnt);
 784                br_read_unlock(vfsmount_lock);
 785                return;
 786        }
 787        br_read_unlock(vfsmount_lock);
 788
 789        br_write_lock(vfsmount_lock);
 790        mnt_dec_count(mnt);
 791        if (mnt_get_count(mnt)) {
 792                br_write_unlock(vfsmount_lock);
 793                return;
 794        }
 795#else
 796        mnt_dec_count(mnt);
 797        if (likely(mnt_get_count(mnt)))
 798                return;
 799        br_write_lock(vfsmount_lock);
 800#endif
 801        if (unlikely(mnt->mnt_pinned)) {
 802                mnt_add_count(mnt, mnt->mnt_pinned + 1);
 803                mnt->mnt_pinned = 0;
 804                br_write_unlock(vfsmount_lock);
 805                acct_auto_close_mnt(mnt);
 806                goto put_again;
 807        }
 808        br_write_unlock(vfsmount_lock);
 809        mntfree(mnt);
 810}
 811
 812void mntput(struct vfsmount *mnt)
 813{
 814        if (mnt) {
 815                /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
 816                if (unlikely(mnt->mnt_expiry_mark))
 817                        mnt->mnt_expiry_mark = 0;
 818                mntput_no_expire(mnt);
 819        }
 820}
 821EXPORT_SYMBOL(mntput);
 822
 823struct vfsmount *mntget(struct vfsmount *mnt)
 824{
 825        if (mnt)
 826                mnt_inc_count(mnt);
 827        return mnt;
 828}
 829EXPORT_SYMBOL(mntget);
 830
 831void mnt_pin(struct vfsmount *mnt)
 832{
 833        br_write_lock(vfsmount_lock);
 834        mnt->mnt_pinned++;
 835        br_write_unlock(vfsmount_lock);
 836}
 837EXPORT_SYMBOL(mnt_pin);
 838
 839void mnt_unpin(struct vfsmount *mnt)
 840{
 841        br_write_lock(vfsmount_lock);
 842        if (mnt->mnt_pinned) {
 843                mnt_inc_count(mnt);
 844                mnt->mnt_pinned--;
 845        }
 846        br_write_unlock(vfsmount_lock);
 847}
 848EXPORT_SYMBOL(mnt_unpin);
 849
 850static inline void mangle(struct seq_file *m, const char *s)
 851{
 852        seq_escape(m, s, " \t\n\\");
 853}
 854
 855/*
 856 * Simple .show_options callback for filesystems which don't want to
 857 * implement more complex mount option showing.
 858 *
 859 * See also save_mount_options().
 860 */
 861int generic_show_options(struct seq_file *m, struct vfsmount *mnt)
 862{
 863        const char *options;
 864
 865        rcu_read_lock();
 866        options = rcu_dereference(mnt->mnt_sb->s_options);
 867
 868        if (options != NULL && options[0]) {
 869                seq_putc(m, ',');
 870                mangle(m, options);
 871        }
 872        rcu_read_unlock();
 873
 874        return 0;
 875}
 876EXPORT_SYMBOL(generic_show_options);
 877
 878/*
 879 * If filesystem uses generic_show_options(), this function should be
 880 * called from the fill_super() callback.
 881 *
 882 * The .remount_fs callback usually needs to be handled in a special
 883 * way, to make sure, that previous options are not overwritten if the
 884 * remount fails.
 885 *
 886 * Also note, that if the filesystem's .remount_fs function doesn't
 887 * reset all options to their default value, but changes only newly
 888 * given options, then the displayed options will not reflect reality
 889 * any more.
 890 */
 891void save_mount_options(struct super_block *sb, char *options)
 892{
 893        BUG_ON(sb->s_options);
 894        rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
 895}
 896EXPORT_SYMBOL(save_mount_options);
 897
 898void replace_mount_options(struct super_block *sb, char *options)
 899{
 900        char *old = sb->s_options;
 901        rcu_assign_pointer(sb->s_options, options);
 902        if (old) {
 903                synchronize_rcu();
 904                kfree(old);
 905        }
 906}
 907EXPORT_SYMBOL(replace_mount_options);
 908
 909#ifdef CONFIG_PROC_FS
 910/* iterator */
 911static void *m_start(struct seq_file *m, loff_t *pos)
 912{
 913        struct proc_mounts *p = m->private;
 914
 915        down_read(&namespace_sem);
 916        return seq_list_start(&p->ns->list, *pos);
 917}
 918
 919static void *m_next(struct seq_file *m, void *v, loff_t *pos)
 920{
 921        struct proc_mounts *p = m->private;
 922
 923        return seq_list_next(v, &p->ns->list, pos);
 924}
 925
 926static void m_stop(struct seq_file *m, void *v)
 927{
 928        up_read(&namespace_sem);
 929}
 930
 931int mnt_had_events(struct proc_mounts *p)
 932{
 933        struct mnt_namespace *ns = p->ns;
 934        int res = 0;
 935
 936        br_read_lock(vfsmount_lock);
 937        if (p->m.poll_event != ns->event) {
 938                p->m.poll_event = ns->event;
 939                res = 1;
 940        }
 941        br_read_unlock(vfsmount_lock);
 942
 943        return res;
 944}
 945
 946struct proc_fs_info {
 947        int flag;
 948        const char *str;
 949};
 950
 951static int show_sb_opts(struct seq_file *m, struct super_block *sb)
 952{
 953        static const struct proc_fs_info fs_info[] = {
 954                { MS_SYNCHRONOUS, ",sync" },
 955                { MS_DIRSYNC, ",dirsync" },
 956                { MS_MANDLOCK, ",mand" },
 957                { 0, NULL }
 958        };
 959        const struct proc_fs_info *fs_infop;
 960
 961        for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
 962                if (sb->s_flags & fs_infop->flag)
 963                        seq_puts(m, fs_infop->str);
 964        }
 965
 966        return security_sb_show_options(m, sb);
 967}
 968
 969static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
 970{
 971        static const struct proc_fs_info mnt_info[] = {
 972                { MNT_NOSUID, ",nosuid" },
 973                { MNT_NODEV, ",nodev" },
 974                { MNT_NOEXEC, ",noexec" },
 975                { MNT_NOATIME, ",noatime" },
 976                { MNT_NODIRATIME, ",nodiratime" },
 977                { MNT_RELATIME, ",relatime" },
 978                { 0, NULL }
 979        };
 980        const struct proc_fs_info *fs_infop;
 981
 982        for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
 983                if (mnt->mnt_flags & fs_infop->flag)
 984                        seq_puts(m, fs_infop->str);
 985        }
 986}
 987
 988static void show_type(struct seq_file *m, struct super_block *sb)
 989{
 990        mangle(m, sb->s_type->name);
 991        if (sb->s_subtype && sb->s_subtype[0]) {
 992                seq_putc(m, '.');
 993                mangle(m, sb->s_subtype);
 994        }
 995}
 996
 997static int show_vfsmnt(struct seq_file *m, void *v)
 998{
 999        struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
1000        int err = 0;
1001        struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
1002
1003        if (mnt->mnt_sb->s_op->show_devname) {
1004                err = mnt->mnt_sb->s_op->show_devname(m, mnt);
1005                if (err)
1006                        goto out;
1007        } else {
1008                mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
1009        }
1010        seq_putc(m, ' ');
1011        seq_path(m, &mnt_path, " \t\n\\");
1012        seq_putc(m, ' ');
1013        show_type(m, mnt->mnt_sb);
1014        seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
1015        err = show_sb_opts(m, mnt->mnt_sb);
1016        if (err)
1017                goto out;
1018        show_mnt_opts(m, mnt);
1019        if (mnt->mnt_sb->s_op->show_options)
1020                err = mnt->mnt_sb->s_op->show_options(m, mnt);
1021        seq_puts(m, " 0 0\n");
1022out:
1023        return err;
1024}
1025
1026const struct seq_operations mounts_op = {
1027        .start  = m_start,
1028        .next   = m_next,
1029        .stop   = m_stop,
1030        .show   = show_vfsmnt
1031};
1032
1033static int show_mountinfo(struct seq_file *m, void *v)
1034{
1035        struct proc_mounts *p = m->private;
1036        struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
1037        struct super_block *sb = mnt->mnt_sb;
1038        struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
1039        struct path root = p->root;
1040        int err = 0;
1041
1042        seq_printf(m, "%i %i %u:%u ", mnt->mnt_id, mnt->mnt_parent->mnt_id,
1043                   MAJOR(sb->s_dev), MINOR(sb->s_dev));
1044        if (sb->s_op->show_path)
1045                err = sb->s_op->show_path(m, mnt);
1046        else
1047                seq_dentry(m, mnt->mnt_root, " \t\n\\");
1048        if (err)
1049                goto out;
1050        seq_putc(m, ' ');
1051
1052        /* mountpoints outside of chroot jail will give SEQ_SKIP on this */
1053        err = seq_path_root(m, &mnt_path, &root, " \t\n\\");
1054        if (err)
1055                goto out;
1056
1057        seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
1058        show_mnt_opts(m, mnt);
1059
1060        /* Tagged fields ("foo:X" or "bar") */
1061        if (IS_MNT_SHARED(mnt))
1062                seq_printf(m, " shared:%i", mnt->mnt_group_id);
1063        if (IS_MNT_SLAVE(mnt)) {
1064                int master = mnt->mnt_master->mnt_group_id;
1065                int dom = get_dominating_id(mnt, &p->root);
1066                seq_printf(m, " master:%i", master);
1067                if (dom && dom != master)
1068                        seq_printf(m, " propagate_from:%i", dom);
1069        }
1070        if (IS_MNT_UNBINDABLE(mnt))
1071                seq_puts(m, " unbindable");
1072
1073        /* Filesystem specific data */
1074        seq_puts(m, " - ");
1075        show_type(m, sb);
1076        seq_putc(m, ' ');
1077        if (sb->s_op->show_devname)
1078                err = sb->s_op->show_devname(m, mnt);
1079        else
1080                mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
1081        if (err)
1082                goto out;
1083        seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
1084        err = show_sb_opts(m, sb);
1085        if (err)
1086                goto out;
1087        if (sb->s_op->show_options)
1088                err = sb->s_op->show_options(m, mnt);
1089        seq_putc(m, '\n');
1090out:
1091        return err;
1092}
1093
1094const struct seq_operations mountinfo_op = {
1095        .start  = m_start,
1096        .next   = m_next,
1097        .stop   = m_stop,
1098        .show   = show_mountinfo,
1099};
1100
1101static int show_vfsstat(struct seq_file *m, void *v)
1102{
1103        struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
1104        struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
1105        int err = 0;
1106
1107        /* device */
1108        if (mnt->mnt_sb->s_op->show_devname) {
1109                seq_puts(m, "device ");
1110                err = mnt->mnt_sb->s_op->show_devname(m, mnt);
1111        } else {
1112                if (mnt->mnt_devname) {
1113                        seq_puts(m, "device ");
1114                        mangle(m, mnt->mnt_devname);
1115                } else
1116                        seq_puts(m, "no device");
1117        }
1118
1119        /* mount point */
1120        seq_puts(m, " mounted on ");
1121        seq_path(m, &mnt_path, " \t\n\\");
1122        seq_putc(m, ' ');
1123
1124        /* file system type */
1125        seq_puts(m, "with fstype ");
1126        show_type(m, mnt->mnt_sb);
1127
1128        /* optional statistics */
1129        if (mnt->mnt_sb->s_op->show_stats) {
1130                seq_putc(m, ' ');
1131                if (!err)
1132                        err = mnt->mnt_sb->s_op->show_stats(m, mnt);
1133        }
1134
1135        seq_putc(m, '\n');
1136        return err;
1137}
1138
1139const struct seq_operations mountstats_op = {
1140        .start  = m_start,
1141        .next   = m_next,
1142        .stop   = m_stop,
1143        .show   = show_vfsstat,
1144};
1145#endif  /* CONFIG_PROC_FS */
1146
1147/**
1148 * may_umount_tree - check if a mount tree is busy
1149 * @mnt: root of mount tree
1150 *
1151 * This is called to check if a tree of mounts has any
1152 * open files, pwds, chroots or sub mounts that are
1153 * busy.
1154 */
1155int may_umount_tree(struct vfsmount *mnt)
1156{
1157        int actual_refs = 0;
1158        int minimum_refs = 0;
1159        struct vfsmount *p;
1160
1161        /* write lock needed for mnt_get_count */
1162        br_write_lock(vfsmount_lock);
1163        for (p = mnt; p; p = next_mnt(p, mnt)) {
1164                actual_refs += mnt_get_count(p);
1165                minimum_refs += 2;
1166        }
1167        br_write_unlock(vfsmount_lock);
1168
1169        if (actual_refs > minimum_refs)
1170                return 0;
1171
1172        return 1;
1173}
1174
1175EXPORT_SYMBOL(may_umount_tree);
1176
1177/**
1178 * may_umount - check if a mount point is busy
1179 * @mnt: root of mount
1180 *
1181 * This is called to check if a mount point has any
1182 * open files, pwds, chroots or sub mounts. If the
1183 * mount has sub mounts this will return busy
1184 * regardless of whether the sub mounts are busy.
1185 *
1186 * Doesn't take quota and stuff into account. IOW, in some cases it will
1187 * give false negatives. The main reason why it's here is that we need
1188 * a non-destructive way to look for easily umountable filesystems.
1189 */
1190int may_umount(struct vfsmount *mnt)
1191{
1192        int ret = 1;
1193        down_read(&namespace_sem);
1194        br_write_lock(vfsmount_lock);
1195        if (propagate_mount_busy(mnt, 2))
1196                ret = 0;
1197        br_write_unlock(vfsmount_lock);
1198        up_read(&namespace_sem);
1199        return ret;
1200}
1201
1202EXPORT_SYMBOL(may_umount);
1203
1204void release_mounts(struct list_head *head)
1205{
1206        struct vfsmount *mnt;
1207        while (!list_empty(head)) {
1208                mnt = list_first_entry(head, struct vfsmount, mnt_hash);
1209                list_del_init(&mnt->mnt_hash);
1210                if (mnt->mnt_parent != mnt) {
1211                        struct dentry *dentry;
1212                        struct vfsmount *m;
1213
1214                        br_write_lock(vfsmount_lock);
1215                        dentry = mnt->mnt_mountpoint;
1216                        m = mnt->mnt_parent;
1217                        mnt->mnt_mountpoint = mnt->mnt_root;
1218                        mnt->mnt_parent = mnt;
1219                        m->mnt_ghosts--;
1220                        br_write_unlock(vfsmount_lock);
1221                        dput(dentry);
1222                        mntput(m);
1223                }
1224                mntput(mnt);
1225        }
1226}
1227
1228/*
1229 * vfsmount lock must be held for write
1230 * namespace_sem must be held for write
1231 */
1232void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
1233{
1234        LIST_HEAD(tmp_list);
1235        struct vfsmount *p;
1236
1237        for (p = mnt; p; p = next_mnt(p, mnt))
1238                list_move(&p->mnt_hash, &tmp_list);
1239
1240        if (propagate)
1241                propagate_umount(&tmp_list);
1242
1243        list_for_each_entry(p, &tmp_list, mnt_hash) {
1244                list_del_init(&p->mnt_expire);
1245                list_del_init(&p->mnt_list);
1246                __touch_mnt_namespace(p->mnt_ns);
1247                p->mnt_ns = NULL;
1248                __mnt_make_shortterm(p);
1249                list_del_init(&p->mnt_child);
1250                if (p->mnt_parent != p) {
1251                        p->mnt_parent->mnt_ghosts++;
1252                        dentry_reset_mounted(p->mnt_parent, p->mnt_mountpoint);
1253                }
1254                change_mnt_propagation(p, MS_PRIVATE);
1255        }
1256        list_splice(&tmp_list, kill);
1257}
1258
1259static void shrink_submounts(struct vfsmount *mnt, struct list_head *umounts);
1260
1261static int do_umount(struct vfsmount *mnt, int flags)
1262{
1263        struct super_block *sb = mnt->mnt_sb;
1264        int retval;
1265        LIST_HEAD(umount_list);
1266
1267        retval = security_sb_umount(mnt, flags);
1268        if (retval)
1269                return retval;
1270
1271        /*
1272         * Allow userspace to request a mountpoint be expired rather than
1273         * unmounting unconditionally. Unmount only happens if:
1274         *  (1) the mark is already set (the mark is cleared by mntput())
1275         *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1276         */
1277        if (flags & MNT_EXPIRE) {
1278                if (mnt == current->fs->root.mnt ||
1279                    flags & (MNT_FORCE | MNT_DETACH))
1280                        return -EINVAL;
1281
1282                /*
1283                 * probably don't strictly need the lock here if we examined
1284                 * all race cases, but it's a slowpath.
1285                 */
1286                br_write_lock(vfsmount_lock);
1287                if (mnt_get_count(mnt) != 2) {
1288                        br_write_unlock(vfsmount_lock);
1289                        return -EBUSY;
1290                }
1291                br_write_unlock(vfsmount_lock);
1292
1293                if (!xchg(&mnt->mnt_expiry_mark, 1))
1294                        return -EAGAIN;
1295        }
1296
1297        /*
1298         * If we may have to abort operations to get out of this
1299         * mount, and they will themselves hold resources we must
1300         * allow the fs to do things. In the Unix tradition of
1301         * 'Gee thats tricky lets do it in userspace' the umount_begin
1302         * might fail to complete on the first run through as other tasks
1303         * must return, and the like. Thats for the mount program to worry
1304         * about for the moment.
1305         */
1306
1307        if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1308                sb->s_op->umount_begin(sb);
1309        }
1310
1311        /*
1312         * No sense to grab the lock for this test, but test itself looks
1313         * somewhat bogus. Suggestions for better replacement?
1314         * Ho-hum... In principle, we might treat that as umount + switch
1315         * to rootfs. GC would eventually take care of the old vfsmount.
1316         * Actually it makes sense, especially if rootfs would contain a
1317         * /reboot - static binary that would close all descriptors and
1318         * call reboot(9). Then init(8) could umount root and exec /reboot.
1319         */
1320        if (mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1321                /*
1322                 * Special case for "unmounting" root ...
1323                 * we just try to remount it readonly.
1324                 */
1325                down_write(&sb->s_umount);
1326                if (!(sb->s_flags & MS_RDONLY))
1327                        retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
1328                up_write(&sb->s_umount);
1329                return retval;
1330        }
1331
1332        down_write(&namespace_sem);
1333        br_write_lock(vfsmount_lock);
1334        event++;
1335
1336        if (!(flags & MNT_DETACH))
1337                shrink_submounts(mnt, &umount_list);
1338
1339        retval = -EBUSY;
1340        if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
1341                if (!list_empty(&mnt->mnt_list))
1342                        umount_tree(mnt, 1, &umount_list);
1343                retval = 0;
1344        }
1345        br_write_unlock(vfsmount_lock);
1346        up_write(&namespace_sem);
1347        release_mounts(&umount_list);
1348        return retval;
1349}
1350
1351/*
1352 * Now umount can handle mount points as well as block devices.
1353 * This is important for filesystems which use unnamed block devices.
1354 *
1355 * We now support a flag for forced unmount like the other 'big iron'
1356 * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1357 */
1358
1359SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1360{
1361        struct path path;
1362        int retval;
1363        int lookup_flags = 0;
1364
1365        if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1366                return -EINVAL;
1367
1368        if (!(flags & UMOUNT_NOFOLLOW))
1369                lookup_flags |= LOOKUP_FOLLOW;
1370
1371        retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
1372        if (retval)
1373                goto out;
1374        retval = -EINVAL;
1375        if (path.dentry != path.mnt->mnt_root)
1376                goto dput_and_out;
1377        if (!check_mnt(path.mnt))
1378                goto dput_and_out;
1379
1380        retval = -EPERM;
1381        if (!capable(CAP_SYS_ADMIN))
1382                goto dput_and_out;
1383
1384        retval = do_umount(path.mnt, flags);
1385dput_and_out:
1386        /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1387        dput(path.dentry);
1388        mntput_no_expire(path.mnt);
1389out:
1390        return retval;
1391}
1392
1393#ifdef __ARCH_WANT_SYS_OLDUMOUNT
1394
1395/*
1396 *      The 2.0 compatible umount. No flags.
1397 */
1398SYSCALL_DEFINE1(oldumount, char __user *, name)
1399{
1400        return sys_umount(name, 0);
1401}
1402
1403#endif
1404
1405static int mount_is_safe(struct path *path)
1406{
1407        if (capable(CAP_SYS_ADMIN))
1408                return 0;
1409        return -EPERM;
1410#ifdef notyet
1411        if (S_ISLNK(path->dentry->d_inode->i_mode))
1412                return -EPERM;
1413        if (path->dentry->d_inode->i_mode & S_ISVTX) {
1414                if (current_uid() != path->dentry->d_inode->i_uid)
1415                        return -EPERM;
1416        }
1417        if (inode_permission(path->dentry->d_inode, MAY_WRITE))
1418                return -EPERM;
1419        return 0;
1420#endif
1421}
1422
1423struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
1424                                        int flag)
1425{
1426        struct vfsmount *res, *p, *q, *r, *s;
1427        struct path path;
1428
1429        if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
1430                return NULL;
1431
1432        res = q = clone_mnt(mnt, dentry, flag);
1433        if (!q)
1434                goto Enomem;
1435        q->mnt_mountpoint = mnt->mnt_mountpoint;
1436
1437        p = mnt;
1438        list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1439                if (!is_subdir(r->mnt_mountpoint, dentry))
1440                        continue;
1441
1442                for (s = r; s; s = next_mnt(s, r)) {
1443                        if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
1444                                s = skip_mnt_tree(s);
1445                                continue;
1446                        }
1447                        while (p != s->mnt_parent) {
1448                                p = p->mnt_parent;
1449                                q = q->mnt_parent;
1450                        }
1451                        p = s;
1452                        path.mnt = q;
1453                        path.dentry = p->mnt_mountpoint;
1454                        q = clone_mnt(p, p->mnt_root, flag);
1455                        if (!q)
1456                                goto Enomem;
1457                        br_write_lock(vfsmount_lock);
1458                        list_add_tail(&q->mnt_list, &res->mnt_list);
1459                        attach_mnt(q, &path);
1460                        br_write_unlock(vfsmount_lock);
1461                }
1462        }
1463        return res;
1464Enomem:
1465        if (res) {
1466                LIST_HEAD(umount_list);
1467                br_write_lock(vfsmount_lock);
1468                umount_tree(res, 0, &umount_list);
1469                br_write_unlock(vfsmount_lock);
1470                release_mounts(&umount_list);
1471        }
1472        return NULL;
1473}
1474
1475struct vfsmount *collect_mounts(struct path *path)
1476{
1477        struct vfsmount *tree;
1478        down_write(&namespace_sem);
1479        tree = copy_tree(path->mnt, path->dentry, CL_COPY_ALL | CL_PRIVATE);
1480        up_write(&namespace_sem);
1481        return tree;
1482}
1483
1484void drop_collected_mounts(struct vfsmount *mnt)
1485{
1486        LIST_HEAD(umount_list);
1487        down_write(&namespace_sem);
1488        br_write_lock(vfsmount_lock);
1489        umount_tree(mnt, 0, &umount_list);
1490        br_write_unlock(vfsmount_lock);
1491        up_write(&namespace_sem);
1492        release_mounts(&umount_list);
1493}
1494
1495int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1496                   struct vfsmount *root)
1497{
1498        struct vfsmount *mnt;
1499        int res = f(root, arg);
1500        if (res)
1501                return res;
1502        list_for_each_entry(mnt, &root->mnt_list, mnt_list) {
1503                res = f(mnt, arg);
1504                if (res)
1505                        return res;
1506        }
1507        return 0;
1508}
1509
1510static void cleanup_group_ids(struct vfsmount *mnt, struct vfsmount *end)
1511{
1512        struct vfsmount *p;
1513
1514        for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1515                if (p->mnt_group_id && !IS_MNT_SHARED(p))
1516                        mnt_release_group_id(p);
1517        }
1518}
1519
1520static int invent_group_ids(struct vfsmount *mnt, bool recurse)
1521{
1522        struct vfsmount *p;
1523
1524        for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1525                if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1526                        int err = mnt_alloc_group_id(p);
1527                        if (err) {
1528                                cleanup_group_ids(mnt, p);
1529                                return err;
1530                        }
1531                }
1532        }
1533
1534        return 0;
1535}
1536
1537/*
1538 *  @source_mnt : mount tree to be attached
1539 *  @nd         : place the mount tree @source_mnt is attached
1540 *  @parent_nd  : if non-null, detach the source_mnt from its parent and
1541 *                 store the parent mount and mountpoint dentry.
1542 *                 (done when source_mnt is moved)
1543 *
1544 *  NOTE: in the table below explains the semantics when a source mount
1545 *  of a given type is attached to a destination mount of a given type.
1546 * ---------------------------------------------------------------------------
1547 * |         BIND MOUNT OPERATION                                            |
1548 * |**************************************************************************
1549 * | source-->| shared        |       private  |       slave    | unbindable |
1550 * | dest     |               |                |                |            |
1551 * |   |      |               |                |                |            |
1552 * |   v      |               |                |                |            |
1553 * |**************************************************************************
1554 * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
1555 * |          |               |                |                |            |
1556 * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
1557 * ***************************************************************************
1558 * A bind operation clones the source mount and mounts the clone on the
1559 * destination mount.
1560 *
1561 * (++)  the cloned mount is propagated to all the mounts in the propagation
1562 *       tree of the destination mount and the cloned mount is added to
1563 *       the peer group of the source mount.
1564 * (+)   the cloned mount is created under the destination mount and is marked
1565 *       as shared. The cloned mount is added to the peer group of the source
1566 *       mount.
1567 * (+++) the mount is propagated to all the mounts in the propagation tree
1568 *       of the destination mount and the cloned mount is made slave
1569 *       of the same master as that of the source mount. The cloned mount
1570 *       is marked as 'shared and slave'.
1571 * (*)   the cloned mount is made a slave of the same master as that of the
1572 *       source mount.
1573 *
1574 * ---------------------------------------------------------------------------
1575 * |                    MOVE MOUNT OPERATION                                 |
1576 * |**************************************************************************
1577 * | source-->| shared        |       private  |       slave    | unbindable |
1578 * | dest     |               |                |                |            |
1579 * |   |      |               |                |                |            |
1580 * |   v      |               |                |                |            |
1581 * |**************************************************************************
1582 * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
1583 * |          |               |                |                |            |
1584 * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
1585 * ***************************************************************************
1586 *
1587 * (+)  the mount is moved to the destination. And is then propagated to
1588 *      all the mounts in the propagation tree of the destination mount.
1589 * (+*)  the mount is moved to the destination.
1590 * (+++)  the mount is moved to the destination and is then propagated to
1591 *      all the mounts belonging to the destination mount's propagation tree.
1592 *      the mount is marked as 'shared and slave'.
1593 * (*)  the mount continues to be a slave at the new location.
1594 *
1595 * if the source mount is a tree, the operations explained above is
1596 * applied to each mount in the tree.
1597 * Must be called without spinlocks held, since this function can sleep
1598 * in allocations.
1599 */
1600static int attach_recursive_mnt(struct vfsmount *source_mnt,
1601                        struct path *path, struct path *parent_path)
1602{
1603        LIST_HEAD(tree_list);
1604        struct vfsmount *dest_mnt = path->mnt;
1605        struct dentry *dest_dentry = path->dentry;
1606        struct vfsmount *child, *p;
1607        int err;
1608
1609        if (IS_MNT_SHARED(dest_mnt)) {
1610                err = invent_group_ids(source_mnt, true);
1611                if (err)
1612                        goto out;
1613        }
1614        err = propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list);
1615        if (err)
1616                goto out_cleanup_ids;
1617
1618        br_write_lock(vfsmount_lock);
1619
1620        if (IS_MNT_SHARED(dest_mnt)) {
1621                for (p = source_mnt; p; p = next_mnt(p, source_mnt))
1622                        set_mnt_shared(p);
1623        }
1624        if (parent_path) {
1625                detach_mnt(source_mnt, parent_path);
1626                attach_mnt(source_mnt, path);
1627                touch_mnt_namespace(parent_path->mnt->mnt_ns);
1628        } else {
1629                mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
1630                commit_tree(source_mnt);
1631        }
1632
1633        list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
1634                list_del_init(&child->mnt_hash);
1635                commit_tree(child);
1636        }
1637        br_write_unlock(vfsmount_lock);
1638
1639        return 0;
1640
1641 out_cleanup_ids:
1642        if (IS_MNT_SHARED(dest_mnt))
1643                cleanup_group_ids(source_mnt, NULL);
1644 out:
1645        return err;
1646}
1647
1648static int lock_mount(struct path *path)
1649{
1650        struct vfsmount *mnt;
1651retry:
1652        mutex_lock(&path->dentry->d_inode->i_mutex);
1653        if (unlikely(cant_mount(path->dentry))) {
1654                mutex_unlock(&path->dentry->d_inode->i_mutex);
1655                return -ENOENT;
1656        }
1657        down_write(&namespace_sem);
1658        mnt = lookup_mnt(path);
1659        if (likely(!mnt))
1660                return 0;
1661        up_write(&namespace_sem);
1662        mutex_unlock(&path->dentry->d_inode->i_mutex);
1663        path_put(path);
1664        path->mnt = mnt;
1665        path->dentry = dget(mnt->mnt_root);
1666        goto retry;
1667}
1668
1669static void unlock_mount(struct path *path)
1670{
1671        up_write(&namespace_sem);
1672        mutex_unlock(&path->dentry->d_inode->i_mutex);
1673}
1674
1675static int graft_tree(struct vfsmount *mnt, struct path *path)
1676{
1677        if (mnt->mnt_sb->s_flags & MS_NOUSER)
1678                return -EINVAL;
1679
1680        if (S_ISDIR(path->dentry->d_inode->i_mode) !=
1681              S_ISDIR(mnt->mnt_root->d_inode->i_mode))
1682                return -ENOTDIR;
1683
1684        if (d_unlinked(path->dentry))
1685                return -ENOENT;
1686
1687        return attach_recursive_mnt(mnt, path, NULL);
1688}
1689
1690/*
1691 * Sanity check the flags to change_mnt_propagation.
1692 */
1693
1694static int flags_to_propagation_type(int flags)
1695{
1696        int type = flags & ~(MS_REC | MS_SILENT);
1697
1698        /* Fail if any non-propagation flags are set */
1699        if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1700                return 0;
1701        /* Only one propagation flag should be set */
1702        if (!is_power_of_2(type))
1703                return 0;
1704        return type;
1705}
1706
1707/*
1708 * recursively change the type of the mountpoint.
1709 */
1710static int do_change_type(struct path *path, int flag)
1711{
1712        struct vfsmount *m, *mnt = path->mnt;
1713        int recurse = flag & MS_REC;
1714        int type;
1715        int err = 0;
1716
1717        if (!capable(CAP_SYS_ADMIN))
1718                return -EPERM;
1719
1720        if (path->dentry != path->mnt->mnt_root)
1721                return -EINVAL;
1722
1723        type = flags_to_propagation_type(flag);
1724        if (!type)
1725                return -EINVAL;
1726
1727        down_write(&namespace_sem);
1728        if (type == MS_SHARED) {
1729                err = invent_group_ids(mnt, recurse);
1730                if (err)
1731                        goto out_unlock;
1732        }
1733
1734        br_write_lock(vfsmount_lock);
1735        for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
1736                change_mnt_propagation(m, type);
1737        br_write_unlock(vfsmount_lock);
1738
1739 out_unlock:
1740        up_write(&namespace_sem);
1741        return err;
1742}
1743
1744/*
1745 * do loopback mount.
1746 */
1747static int do_loopback(struct path *path, char *old_name,
1748                                int recurse)
1749{
1750        LIST_HEAD(umount_list);
1751        struct path old_path;
1752        struct vfsmount *mnt = NULL;
1753        int err = mount_is_safe(path);
1754        if (err)
1755                return err;
1756        if (!old_name || !*old_name)
1757                return -EINVAL;
1758        err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
1759        if (err)
1760                return err;
1761
1762        err = lock_mount(path);
1763        if (err)
1764                goto out;
1765
1766        err = -EINVAL;
1767        if (IS_MNT_UNBINDABLE(old_path.mnt))
1768                goto out2;
1769
1770        if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt))
1771                goto out2;
1772
1773        err = -ENOMEM;
1774        if (recurse)
1775                mnt = copy_tree(old_path.mnt, old_path.dentry, 0);
1776        else
1777                mnt = clone_mnt(old_path.mnt, old_path.dentry, 0);
1778
1779        if (!mnt)
1780                goto out2;
1781
1782        err = graft_tree(mnt, path);
1783        if (err) {
1784                br_write_lock(vfsmount_lock);
1785                umount_tree(mnt, 0, &umount_list);
1786                br_write_unlock(vfsmount_lock);
1787        }
1788out2:
1789        unlock_mount(path);
1790        release_mounts(&umount_list);
1791out:
1792        path_put(&old_path);
1793        return err;
1794}
1795
1796static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
1797{
1798        int error = 0;
1799        int readonly_request = 0;
1800
1801        if (ms_flags & MS_RDONLY)
1802                readonly_request = 1;
1803        if (readonly_request == __mnt_is_readonly(mnt))
1804                return 0;
1805
1806        if (readonly_request)
1807                error = mnt_make_readonly(mnt);
1808        else
1809                __mnt_unmake_readonly(mnt);
1810        return error;
1811}
1812
1813/*
1814 * change filesystem flags. dir should be a physical root of filesystem.
1815 * If you've mounted a non-root directory somewhere and want to do remount
1816 * on it - tough luck.
1817 */
1818static int do_remount(struct path *path, int flags, int mnt_flags,
1819                      void *data)
1820{
1821        int err;
1822        struct super_block *sb = path->mnt->mnt_sb;
1823
1824        if (!capable(CAP_SYS_ADMIN))
1825                return -EPERM;
1826
1827        if (!check_mnt(path->mnt))
1828                return -EINVAL;
1829
1830        if (path->dentry != path->mnt->mnt_root)
1831                return -EINVAL;
1832
1833        err = security_sb_remount(sb, data);
1834        if (err)
1835                return err;
1836
1837        down_write(&sb->s_umount);
1838        if (flags & MS_BIND)
1839                err = change_mount_flags(path->mnt, flags);
1840        else
1841                err = do_remount_sb(sb, flags, data, 0);
1842        if (!err) {
1843                br_write_lock(vfsmount_lock);
1844                mnt_flags |= path->mnt->mnt_flags & MNT_PROPAGATION_MASK;
1845                path->mnt->mnt_flags = mnt_flags;
1846                br_write_unlock(vfsmount_lock);
1847        }
1848        up_write(&sb->s_umount);
1849        if (!err) {
1850                br_write_lock(vfsmount_lock);
1851                touch_mnt_namespace(path->mnt->mnt_ns);
1852                br_write_unlock(vfsmount_lock);
1853        }
1854        return err;
1855}
1856
1857static inline int tree_contains_unbindable(struct vfsmount *mnt)
1858{
1859        struct vfsmount *p;
1860        for (p = mnt; p; p = next_mnt(p, mnt)) {
1861                if (IS_MNT_UNBINDABLE(p))
1862                        return 1;
1863        }
1864        return 0;
1865}
1866
1867static int do_move_mount(struct path *path, char *old_name)
1868{
1869        struct path old_path, parent_path;
1870        struct vfsmount *p;
1871        int err = 0;
1872        if (!capable(CAP_SYS_ADMIN))
1873                return -EPERM;
1874        if (!old_name || !*old_name)
1875                return -EINVAL;
1876        err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
1877        if (err)
1878                return err;
1879
1880        err = lock_mount(path);
1881        if (err < 0)
1882                goto out;
1883
1884        err = -EINVAL;
1885        if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt))
1886                goto out1;
1887
1888        if (d_unlinked(path->dentry))
1889                goto out1;
1890
1891        err = -EINVAL;
1892        if (old_path.dentry != old_path.mnt->mnt_root)
1893                goto out1;
1894
1895        if (old_path.mnt == old_path.mnt->mnt_parent)
1896                goto out1;
1897
1898        if (S_ISDIR(path->dentry->d_inode->i_mode) !=
1899              S_ISDIR(old_path.dentry->d_inode->i_mode))
1900                goto out1;
1901        /*
1902         * Don't move a mount residing in a shared parent.
1903         */
1904        if (old_path.mnt->mnt_parent &&
1905            IS_MNT_SHARED(old_path.mnt->mnt_parent))
1906                goto out1;
1907        /*
1908         * Don't move a mount tree containing unbindable mounts to a destination
1909         * mount which is shared.
1910         */
1911        if (IS_MNT_SHARED(path->mnt) &&
1912            tree_contains_unbindable(old_path.mnt))
1913                goto out1;
1914        err = -ELOOP;
1915        for (p = path->mnt; p->mnt_parent != p; p = p->mnt_parent)
1916                if (p == old_path.mnt)
1917                        goto out1;
1918
1919        err = attach_recursive_mnt(old_path.mnt, path, &parent_path);
1920        if (err)
1921                goto out1;
1922
1923        /* if the mount is moved, it should no longer be expire
1924         * automatically */
1925        list_del_init(&old_path.mnt->mnt_expire);
1926out1:
1927        unlock_mount(path);
1928out:
1929        if (!err)
1930                path_put(&parent_path);
1931        path_put(&old_path);
1932        return err;
1933}
1934
1935static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
1936{
1937        int err;
1938        const char *subtype = strchr(fstype, '.');
1939        if (subtype) {
1940                subtype++;
1941                err = -EINVAL;
1942                if (!subtype[0])
1943                        goto err;
1944        } else
1945                subtype = "";
1946
1947        mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
1948        err = -ENOMEM;
1949        if (!mnt->mnt_sb->s_subtype)
1950                goto err;
1951        return mnt;
1952
1953 err:
1954        mntput(mnt);
1955        return ERR_PTR(err);
1956}
1957
1958struct vfsmount *
1959do_kern_mount(const char *fstype, int flags, const char *name, void *data)
1960{
1961        struct file_system_type *type = get_fs_type(fstype);
1962        struct vfsmount *mnt;
1963        if (!type)
1964                return ERR_PTR(-ENODEV);
1965        mnt = vfs_kern_mount(type, flags, name, data);
1966        if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
1967            !mnt->mnt_sb->s_subtype)
1968                mnt = fs_set_subtype(mnt, fstype);
1969        put_filesystem(type);
1970        return mnt;
1971}
1972EXPORT_SYMBOL_GPL(do_kern_mount);
1973
1974/*
1975 * add a mount into a namespace's mount tree
1976 */
1977static int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
1978{
1979        int err;
1980
1981        mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
1982
1983        err = lock_mount(path);
1984        if (err)
1985                return err;
1986
1987        err = -EINVAL;
1988        if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(path->mnt))
1989                goto unlock;
1990
1991        /* Refuse the same filesystem on the same mount point */
1992        err = -EBUSY;
1993        if (path->mnt->mnt_sb == newmnt->mnt_sb &&
1994            path->mnt->mnt_root == path->dentry)
1995                goto unlock;
1996
1997        err = -EINVAL;
1998        if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
1999                goto unlock;
2000
2001        newmnt->mnt_flags = mnt_flags;
2002        err = graft_tree(newmnt, path);
2003
2004unlock:
2005        unlock_mount(path);
2006        return err;
2007}
2008
2009/*
2010 * create a new mount for userspace and request it to be added into the
2011 * namespace's tree
2012 */
2013static int do_new_mount(struct path *path, char *type, int flags,
2014                        int mnt_flags, char *name, void *data)
2015{
2016        struct vfsmount *mnt;
2017        int err;
2018
2019        if (!type)
2020                return -EINVAL;
2021
2022        /* we need capabilities... */
2023        if (!capable(CAP_SYS_ADMIN))
2024                return -EPERM;
2025
2026        mnt = do_kern_mount(type, flags, name, data);
2027        if (IS_ERR(mnt))
2028                return PTR_ERR(mnt);
2029
2030        err = do_add_mount(mnt, path, mnt_flags);
2031        if (err)
2032                mntput(mnt);
2033        return err;
2034}
2035
2036int finish_automount(struct vfsmount *m, struct path *path)
2037{
2038        int err;
2039        /* The new mount record should have at least 2 refs to prevent it being
2040         * expired before we get a chance to add it
2041         */
2042        BUG_ON(mnt_get_count(m) < 2);
2043
2044        if (m->mnt_sb == path->mnt->mnt_sb &&
2045            m->mnt_root == path->dentry) {
2046                err = -ELOOP;
2047                goto fail;
2048        }
2049
2050        err = do_add_mount(m, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2051        if (!err)
2052                return 0;
2053fail:
2054        /* remove m from any expiration list it may be on */
2055        if (!list_empty(&m->mnt_expire)) {
2056                down_write(&namespace_sem);
2057                br_write_lock(vfsmount_lock);
2058                list_del_init(&m->mnt_expire);
2059                br_write_unlock(vfsmount_lock);
2060                up_write(&namespace_sem);
2061        }
2062        mntput(m);
2063        mntput(m);
2064        return err;
2065}
2066
2067/**
2068 * mnt_set_expiry - Put a mount on an expiration list
2069 * @mnt: The mount to list.
2070 * @expiry_list: The list to add the mount to.
2071 */
2072void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2073{
2074        down_write(&namespace_sem);
2075        br_write_lock(vfsmount_lock);
2076
2077        list_add_tail(&mnt->mnt_expire, expiry_list);
2078
2079        br_write_unlock(vfsmount_lock);
2080        up_write(&namespace_sem);
2081}
2082EXPORT_SYMBOL(mnt_set_expiry);
2083
2084/*
2085 * process a list of expirable mountpoints with the intent of discarding any
2086 * mountpoints that aren't in use and haven't been touched since last we came
2087 * here
2088 */
2089void mark_mounts_for_expiry(struct list_head *mounts)
2090{
2091        struct vfsmount *mnt, *next;
2092        LIST_HEAD(graveyard);
2093        LIST_HEAD(umounts);
2094
2095        if (list_empty(mounts))
2096                return;
2097
2098        down_write(&namespace_sem);
2099        br_write_lock(vfsmount_lock);
2100
2101        /* extract from the expiration list every vfsmount that matches the
2102         * following criteria:
2103         * - only referenced by its parent vfsmount
2104         * - still marked for expiry (marked on the last call here; marks are
2105         *   cleared by mntput())
2106         */
2107        list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2108                if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2109                        propagate_mount_busy(mnt, 1))
2110                        continue;
2111                list_move(&mnt->mnt_expire, &graveyard);
2112        }
2113        while (!list_empty(&graveyard)) {
2114                mnt = list_first_entry(&graveyard, struct vfsmount, mnt_expire);
2115                touch_mnt_namespace(mnt->mnt_ns);
2116                umount_tree(mnt, 1, &umounts);
2117        }
2118        br_write_unlock(vfsmount_lock);
2119        up_write(&namespace_sem);
2120
2121        release_mounts(&umounts);
2122}
2123
2124EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2125
2126/*
2127 * Ripoff of 'select_parent()'
2128 *
2129 * search the list of submounts for a given mountpoint, and move any
2130 * shrinkable submounts to the 'graveyard' list.
2131 */
2132static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
2133{
2134        struct vfsmount *this_parent = parent;
2135        struct list_head *next;
2136        int found = 0;
2137
2138repeat:
2139        next = this_parent->mnt_mounts.next;
2140resume:
2141        while (next != &this_parent->mnt_mounts) {
2142                struct list_head *tmp = next;
2143                struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);
2144
2145                next = tmp->next;
2146                if (!(mnt->mnt_flags & MNT_SHRINKABLE))
2147                        continue;
2148                /*
2149                 * Descend a level if the d_mounts list is non-empty.
2150                 */
2151                if (!list_empty(&mnt->mnt_mounts)) {
2152                        this_parent = mnt;
2153                        goto repeat;
2154                }
2155
2156                if (!propagate_mount_busy(mnt, 1)) {
2157                        list_move_tail(&mnt->mnt_expire, graveyard);
2158                        found++;
2159                }
2160        }
2161        /*
2162         * All done at this level ... ascend and resume the search
2163         */
2164        if (this_parent != parent) {
2165                next = this_parent->mnt_child.next;
2166                this_parent = this_parent->mnt_parent;
2167                goto resume;
2168        }
2169        return found;
2170}
2171
2172/*
2173 * process a list of expirable mountpoints with the intent of discarding any
2174 * submounts of a specific parent mountpoint
2175 *
2176 * vfsmount_lock must be held for write
2177 */
2178static void shrink_submounts(struct vfsmount *mnt, struct list_head *umounts)
2179{
2180        LIST_HEAD(graveyard);
2181        struct vfsmount *m;
2182
2183        /* extract submounts of 'mountpoint' from the expiration list */
2184        while (select_submounts(mnt, &graveyard)) {
2185                while (!list_empty(&graveyard)) {
2186                        m = list_first_entry(&graveyard, struct vfsmount,
2187                                                mnt_expire);
2188                        touch_mnt_namespace(m->mnt_ns);
2189                        umount_tree(m, 1, umounts);
2190                }
2191        }
2192}
2193
2194/*
2195 * Some copy_from_user() implementations do not return the exact number of
2196 * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
2197 * Note that this function differs from copy_from_user() in that it will oops
2198 * on bad values of `to', rather than returning a short copy.
2199 */
2200static long exact_copy_from_user(void *to, const void __user * from,
2201                                 unsigned long n)
2202{
2203        char *t = to;
2204        const char __user *f = from;
2205        char c;
2206
2207        if (!access_ok(VERIFY_READ, from, n))
2208                return n;
2209
2210        while (n) {
2211                if (__get_user(c, f)) {
2212                        memset(t, 0, n);
2213                        break;
2214                }
2215                *t++ = c;
2216                f++;
2217                n--;
2218        }
2219        return n;
2220}
2221
2222int copy_mount_options(const void __user * data, unsigned long *where)
2223{
2224        int i;
2225        unsigned long page;
2226        unsigned long size;
2227
2228        *where = 0;
2229        if (!data)
2230                return 0;
2231
2232        if (!(page = __get_free_page(GFP_KERNEL)))
2233                return -ENOMEM;
2234
2235        /* We only care that *some* data at the address the user
2236         * gave us is valid.  Just in case, we'll zero
2237         * the remainder of the page.
2238         */
2239        /* copy_from_user cannot cross TASK_SIZE ! */
2240        size = TASK_SIZE - (unsigned long)data;
2241        if (size > PAGE_SIZE)
2242                size = PAGE_SIZE;
2243
2244        i = size - exact_copy_from_user((void *)page, data, size);
2245        if (!i) {
2246                free_page(page);
2247                return -EFAULT;
2248        }
2249        if (i != PAGE_SIZE)
2250                memset((char *)page + i, 0, PAGE_SIZE - i);
2251        *where = page;
2252        return 0;
2253}
2254
2255int copy_mount_string(const void __user *data, char **where)
2256{
2257        char *tmp;
2258
2259        if (!data) {
2260                *where = NULL;
2261                return 0;
2262        }
2263
2264        tmp = strndup_user(data, PAGE_SIZE);
2265        if (IS_ERR(tmp))
2266                return PTR_ERR(tmp);
2267
2268        *where = tmp;
2269        return 0;
2270}
2271
2272/*
2273 * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
2274 * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
2275 *
2276 * data is a (void *) that can point to any structure up to
2277 * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
2278 * information (or be NULL).
2279 *
2280 * Pre-0.97 versions of mount() didn't have a flags word.
2281 * When the flags word was introduced its top half was required
2282 * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
2283 * Therefore, if this magic number is present, it carries no information
2284 * and must be discarded.
2285 */
2286long do_mount(char *dev_name, char *dir_name, char *type_page,
2287                  unsigned long flags, void *data_page)
2288{
2289        struct path path;
2290        int retval = 0;
2291        int mnt_flags = 0;
2292
2293        /* Discard magic */
2294        if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
2295                flags &= ~MS_MGC_MSK;
2296
2297        /* Basic sanity checks */
2298
2299        if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
2300                return -EINVAL;
2301
2302        if (data_page)
2303                ((char *)data_page)[PAGE_SIZE - 1] = 0;
2304
2305        /* ... and get the mountpoint */
2306        retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
2307        if (retval)
2308                return retval;
2309
2310        retval = security_sb_mount(dev_name, &path,
2311                                   type_page, flags, data_page);
2312        if (retval)
2313                goto dput_out;
2314
2315        /* Default to relatime unless overriden */
2316        if (!(flags & MS_NOATIME))
2317                mnt_flags |= MNT_RELATIME;
2318
2319        /* Separate the per-mountpoint flags */
2320        if (flags & MS_NOSUID)
2321                mnt_flags |= MNT_NOSUID;
2322        if (flags & MS_NODEV)
2323                mnt_flags |= MNT_NODEV;
2324        if (flags & MS_NOEXEC)
2325                mnt_flags |= MNT_NOEXEC;
2326        if (flags & MS_NOATIME)
2327                mnt_flags |= MNT_NOATIME;
2328        if (flags & MS_NODIRATIME)
2329                mnt_flags |= MNT_NODIRATIME;
2330        if (flags & MS_STRICTATIME)
2331                mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
2332        if (flags & MS_RDONLY)
2333                mnt_flags |= MNT_READONLY;
2334
2335        flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
2336                   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
2337                   MS_STRICTATIME);
2338
2339        if (flags & MS_REMOUNT)
2340                retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
2341                                    data_page);
2342        else if (flags & MS_BIND)
2343                retval = do_loopback(&path, dev_name, flags & MS_REC);
2344        else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2345                retval = do_change_type(&path, flags);
2346        else if (flags & MS_MOVE)
2347                retval = do_move_mount(&path, dev_name);
2348        else
2349                retval = do_new_mount(&path, type_page, flags, mnt_flags,
2350                                      dev_name, data_page);
2351dput_out:
2352        path_put(&path);
2353        return retval;
2354}
2355
2356static struct mnt_namespace *alloc_mnt_ns(void)
2357{
2358        struct mnt_namespace *new_ns;
2359
2360        new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
2361        if (!new_ns)
2362                return ERR_PTR(-ENOMEM);
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        return new_ns;
2369}
2370
2371void mnt_make_longterm(struct vfsmount *mnt)
2372{
2373        __mnt_make_longterm(mnt);
2374}
2375
2376void mnt_make_shortterm(struct vfsmount *mnt)
2377{
2378#ifdef CONFIG_SMP
2379        if (atomic_add_unless(&mnt->mnt_longterm, -1, 1))
2380                return;
2381        br_write_lock(vfsmount_lock);
2382        atomic_dec(&mnt->mnt_longterm);
2383        br_write_unlock(vfsmount_lock);
2384#endif
2385}
2386
2387/*
2388 * Allocate a new namespace structure and populate it with contents
2389 * copied from the namespace of the passed in task structure.
2390 */
2391static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
2392                struct fs_struct *fs)
2393{
2394        struct mnt_namespace *new_ns;
2395        struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
2396        struct vfsmount *p, *q;
2397
2398        new_ns = alloc_mnt_ns();
2399        if (IS_ERR(new_ns))
2400                return new_ns;
2401
2402        down_write(&namespace_sem);
2403        /* First pass: copy the tree topology */
2404        new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
2405                                        CL_COPY_ALL | CL_EXPIRE);
2406        if (!new_ns->root) {
2407                up_write(&namespace_sem);
2408                kfree(new_ns);
2409                return ERR_PTR(-ENOMEM);
2410        }
2411        br_write_lock(vfsmount_lock);
2412        list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
2413        br_write_unlock(vfsmount_lock);
2414
2415        /*
2416         * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
2417         * as belonging to new namespace.  We have already acquired a private
2418         * fs_struct, so tsk->fs->lock is not needed.
2419         */
2420        p = mnt_ns->root;
2421        q = new_ns->root;
2422        while (p) {
2423                q->mnt_ns = new_ns;
2424                __mnt_make_longterm(q);
2425                if (fs) {
2426                        if (p == fs->root.mnt) {
2427                                fs->root.mnt = mntget(q);
2428                                __mnt_make_longterm(q);
2429                                mnt_make_shortterm(p);
2430                                rootmnt = p;
2431                        }
2432                        if (p == fs->pwd.mnt) {
2433                                fs->pwd.mnt = mntget(q);
2434                                __mnt_make_longterm(q);
2435                                mnt_make_shortterm(p);
2436                                pwdmnt = p;
2437                        }
2438                }
2439                p = next_mnt(p, mnt_ns->root);
2440                q = next_mnt(q, new_ns->root);
2441        }
2442        up_write(&namespace_sem);
2443
2444        if (rootmnt)
2445                mntput(rootmnt);
2446        if (pwdmnt)
2447                mntput(pwdmnt);
2448
2449        return new_ns;
2450}
2451
2452struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
2453                struct fs_struct *new_fs)
2454{
2455        struct mnt_namespace *new_ns;
2456
2457        BUG_ON(!ns);
2458        get_mnt_ns(ns);
2459
2460        if (!(flags & CLONE_NEWNS))
2461                return ns;
2462
2463        new_ns = dup_mnt_ns(ns, new_fs);
2464
2465        put_mnt_ns(ns);
2466        return new_ns;
2467}
2468
2469/**
2470 * create_mnt_ns - creates a private namespace and adds a root filesystem
2471 * @mnt: pointer to the new root filesystem mountpoint
2472 */
2473struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
2474{
2475        struct mnt_namespace *new_ns;
2476
2477        new_ns = alloc_mnt_ns();
2478        if (!IS_ERR(new_ns)) {
2479                mnt->mnt_ns = new_ns;
2480                __mnt_make_longterm(mnt);
2481                new_ns->root = mnt;
2482                list_add(&new_ns->list, &new_ns->root->mnt_list);
2483        }
2484        return new_ns;
2485}
2486EXPORT_SYMBOL(create_mnt_ns);
2487
2488SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
2489                char __user *, type, unsigned long, flags, void __user *, data)
2490{
2491        int ret;
2492        char *kernel_type;
2493        char *kernel_dir;
2494        char *kernel_dev;
2495        unsigned long data_page;
2496
2497        ret = copy_mount_string(type, &kernel_type);
2498        if (ret < 0)
2499                goto out_type;
2500
2501        kernel_dir = getname(dir_name);
2502        if (IS_ERR(kernel_dir)) {
2503                ret = PTR_ERR(kernel_dir);
2504                goto out_dir;
2505        }
2506
2507        ret = copy_mount_string(dev_name, &kernel_dev);
2508        if (ret < 0)
2509                goto out_dev;
2510
2511        ret = copy_mount_options(data, &data_page);
2512        if (ret < 0)
2513                goto out_data;
2514
2515        ret = do_mount(kernel_dev, kernel_dir, kernel_type, flags,
2516                (void *) data_page);
2517
2518        free_page(data_page);
2519out_data:
2520        kfree(kernel_dev);
2521out_dev:
2522        putname(kernel_dir);
2523out_dir:
2524        kfree(kernel_type);
2525out_type:
2526        return ret;
2527}
2528
2529/*
2530 * pivot_root Semantics:
2531 * Moves the root file system of the current process to the directory put_old,
2532 * makes new_root as the new root file system of the current process, and sets
2533 * root/cwd of all processes which had them on the current root to new_root.
2534 *
2535 * Restrictions:
2536 * The new_root and put_old must be directories, and  must not be on the
2537 * same file  system as the current process root. The put_old  must  be
2538 * underneath new_root,  i.e. adding a non-zero number of /.. to the string
2539 * pointed to by put_old must yield the same directory as new_root. No other
2540 * file system may be mounted on put_old. After all, new_root is a mountpoint.
2541 *
2542 * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
2543 * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
2544 * in this situation.
2545 *
2546 * Notes:
2547 *  - we don't move root/cwd if they are not at the root (reason: if something
2548 *    cared enough to change them, it's probably wrong to force them elsewhere)
2549 *  - it's okay to pick a root that isn't the root of a file system, e.g.
2550 *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
2551 *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
2552 *    first.
2553 */
2554SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
2555                const char __user *, put_old)
2556{
2557        struct vfsmount *tmp;
2558        struct path new, old, parent_path, root_parent, root;
2559        int error;
2560
2561        if (!capable(CAP_SYS_ADMIN))
2562                return -EPERM;
2563
2564        error = user_path_dir(new_root, &new);
2565        if (error)
2566                goto out0;
2567
2568        error = user_path_dir(put_old, &old);
2569        if (error)
2570                goto out1;
2571
2572        error = security_sb_pivotroot(&old, &new);
2573        if (error)
2574                goto out2;
2575
2576        get_fs_root(current->fs, &root);
2577        error = lock_mount(&old);
2578        if (error)
2579                goto out3;
2580
2581        error = -EINVAL;
2582        if (IS_MNT_SHARED(old.mnt) ||
2583                IS_MNT_SHARED(new.mnt->mnt_parent) ||
2584                IS_MNT_SHARED(root.mnt->mnt_parent))
2585                goto out4;
2586        if (!check_mnt(root.mnt) || !check_mnt(new.mnt))
2587                goto out4;
2588        error = -ENOENT;
2589        if (d_unlinked(new.dentry))
2590                goto out4;
2591        if (d_unlinked(old.dentry))
2592                goto out4;
2593        error = -EBUSY;
2594        if (new.mnt == root.mnt ||
2595            old.mnt == root.mnt)
2596                goto out4; /* loop, on the same file system  */
2597        error = -EINVAL;
2598        if (root.mnt->mnt_root != root.dentry)
2599                goto out4; /* not a mountpoint */
2600        if (root.mnt->mnt_parent == root.mnt)
2601                goto out4; /* not attached */
2602        if (new.mnt->mnt_root != new.dentry)
2603                goto out4; /* not a mountpoint */
2604        if (new.mnt->mnt_parent == new.mnt)
2605                goto out4; /* not attached */
2606        /* make sure we can reach put_old from new_root */
2607        tmp = old.mnt;
2608        if (tmp != new.mnt) {
2609                for (;;) {
2610                        if (tmp->mnt_parent == tmp)
2611                                goto out4; /* already mounted on put_old */
2612                        if (tmp->mnt_parent == new.mnt)
2613                                break;
2614                        tmp = tmp->mnt_parent;
2615                }
2616                if (!is_subdir(tmp->mnt_mountpoint, new.dentry))
2617                        goto out4;
2618        } else if (!is_subdir(old.dentry, new.dentry))
2619                goto out4;
2620        br_write_lock(vfsmount_lock);
2621        detach_mnt(new.mnt, &parent_path);
2622        detach_mnt(root.mnt, &root_parent);
2623        /* mount old root on put_old */
2624        attach_mnt(root.mnt, &old);
2625        /* mount new_root on / */
2626        attach_mnt(new.mnt, &root_parent);
2627        touch_mnt_namespace(current->nsproxy->mnt_ns);
2628        br_write_unlock(vfsmount_lock);
2629        chroot_fs_refs(&root, &new);
2630        error = 0;
2631out4:
2632        unlock_mount(&old);
2633        if (!error) {
2634                path_put(&root_parent);
2635                path_put(&parent_path);
2636        }
2637out3:
2638        path_put(&root);
2639out2:
2640        path_put(&old);
2641out1:
2642        path_put(&new);
2643out0:
2644        return error;
2645}
2646
2647static void __init init_mount_tree(void)
2648{
2649        struct vfsmount *mnt;
2650        struct mnt_namespace *ns;
2651        struct path root;
2652
2653        mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
2654        if (IS_ERR(mnt))
2655                panic("Can't create rootfs");
2656
2657        ns = create_mnt_ns(mnt);
2658        if (IS_ERR(ns))
2659                panic("Can't allocate initial namespace");
2660
2661        init_task.nsproxy->mnt_ns = ns;
2662        get_mnt_ns(ns);
2663
2664        root.mnt = ns->root;
2665        root.dentry = ns->root->mnt_root;
2666
2667        set_fs_pwd(current->fs, &root);
2668        set_fs_root(current->fs, &root);
2669}
2670
2671void __init mnt_init(void)
2672{
2673        unsigned u;
2674        int err;
2675
2676        init_rwsem(&namespace_sem);
2677
2678        mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
2679                        0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
2680
2681        mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
2682
2683        if (!mount_hashtable)
2684                panic("Failed to allocate mount hash table\n");
2685
2686        printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
2687
2688        for (u = 0; u < HASH_SIZE; u++)
2689                INIT_LIST_HEAD(&mount_hashtable[u]);
2690
2691        br_lock_init(vfsmount_lock);
2692
2693        err = sysfs_init();
2694        if (err)
2695                printk(KERN_WARNING "%s: sysfs_init error: %d\n",
2696                        __func__, err);
2697        fs_kobj = kobject_create_and_add("fs", NULL);
2698        if (!fs_kobj)
2699                printk(KERN_WARNING "%s: kobj create error\n", __func__);
2700        init_rootfs();
2701        init_mount_tree();
2702}
2703
2704void put_mnt_ns(struct mnt_namespace *ns)
2705{
2706        LIST_HEAD(umount_list);
2707
2708        if (!atomic_dec_and_test(&ns->count))
2709                return;
2710        down_write(&namespace_sem);
2711        br_write_lock(vfsmount_lock);
2712        umount_tree(ns->root, 0, &umount_list);
2713        br_write_unlock(vfsmount_lock);
2714        up_write(&namespace_sem);
2715        release_mounts(&umount_list);
2716        kfree(ns);
2717}
2718EXPORT_SYMBOL(put_mnt_ns);
2719
2720struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
2721{
2722        struct vfsmount *mnt;
2723        mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
2724        if (!IS_ERR(mnt)) {
2725                /*
2726                 * it is a longterm mount, don't release mnt until
2727                 * we unmount before file sys is unregistered
2728                */
2729                mnt_make_longterm(mnt);
2730        }
2731        return mnt;
2732}
2733EXPORT_SYMBOL_GPL(kern_mount_data);
2734
2735void kern_unmount(struct vfsmount *mnt)
2736{
2737        /* release long term mount so mount point can be released */
2738        if (!IS_ERR_OR_NULL(mnt)) {
2739                mnt_make_shortterm(mnt);
2740                mntput(mnt);
2741        }
2742}
2743EXPORT_SYMBOL(kern_unmount);
2744
2745bool our_mnt(struct vfsmount *mnt)
2746{
2747        return check_mnt(mnt);
2748}
2749
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