fs/namespace.c

   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/smp_lock.h>
  15 #include <linux/init.h>
  16 #include <linux/kernel.h>
  17 #include <linux/quotaops.h>
  18 #include <linux/acct.h>
  19 #include <linux/capability.h>
  20 #include <linux/module.h>
  21 #include <linux/sysfs.h>
  22 #include <linux/seq_file.h>
  23 #include <linux/mnt_namespace.h>
  24 #include <linux/namei.h>
  25 #include <linux/security.h>
  26 #include <linux/mount.h>
  27 #include <linux/ramfs.h>
  28 #include <asm/uaccess.h>
  29 #include <asm/unistd.h>
  30 #include "pnode.h"
  31 #include "internal.h"
  32
  33 /* spinlock for vfsmount related operations, inplace of dcache_lock */
  34 __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
  35
  36 static int event;
  37
  38 static struct list_head *mount_hashtable __read_mostly;
  39 static int hash_mask __read_mostly, hash_bits __read_mostly;
  40 static struct kmem_cache *mnt_cache __read_mostly;
  41 static struct rw_semaphore namespace_sem;
  42
  43 /* /sys/fs */
  44 decl_subsys(fs, NULL, NULL);
  45 EXPORT_SYMBOL_GPL(fs_subsys);
  46
  47 static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
  48 {
  49         unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
  50         tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
  51         tmp = tmp + (tmp >> hash_bits);
  52         return tmp & hash_mask;
  53 }
  54
  55 struct vfsmount *alloc_vfsmnt(const char *name)
  56 {
  57         struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
  58         if (mnt) {
  59                 atomic_set(&mnt->mnt_count, 1);
  60                 INIT_LIST_HEAD(&mnt->mnt_hash);
  61                 INIT_LIST_HEAD(&mnt->mnt_child);
  62                 INIT_LIST_HEAD(&mnt->mnt_mounts);
  63                 INIT_LIST_HEAD(&mnt->mnt_list);
  64                 INIT_LIST_HEAD(&mnt->mnt_expire);
  65                 INIT_LIST_HEAD(&mnt->mnt_share);
  66                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
  67                 INIT_LIST_HEAD(&mnt->mnt_slave);
  68                 if (name) {
  69                         int size = strlen(name) + 1;
  70                         char *newname = kmalloc(size, GFP_KERNEL);
  71                         if (newname) {
  72                                 memcpy(newname, name, size);
  73                                 mnt->mnt_devname = newname;
  74                         }
  75                 }
  76         }
  77         return mnt;
  78 }
  79
  80 int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
  81 {
  82         mnt->mnt_sb = sb;
  83         mnt->mnt_root = dget(sb->s_root);
  84         return 0;
  85 }
  86
  87 EXPORT_SYMBOL(simple_set_mnt);
  88
  89 void free_vfsmnt(struct vfsmount *mnt)
  90 {
  91         kfree(mnt->mnt_devname);
  92         kmem_cache_free(mnt_cache, mnt);
  93 }
  94
  95 /*
  96  * find the first or last mount at @dentry on vfsmount @mnt depending on
  97  * @dir. If @dir is set return the first mount else return the last mount.
  98  */
  99 struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
 100                               int dir)
 101 {
 102         struct list_head *head = mount_hashtable + hash(mnt, dentry);
 103         struct list_head *tmp = head;
 104         struct vfsmount *p, *found = NULL;
 105
 106         for (;;) {
 107                 tmp = dir ? tmp->next : tmp->prev;
 108                 p = NULL;
 109                 if (tmp == head)
 110                         break;
 111                 p = list_entry(tmp, struct vfsmount, mnt_hash);
 112                 if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
 113                         found = p;
 114                         break;
 115                 }
 116         }
 117         return found;
 118 }
 119
 120 /*
 121  * lookup_mnt increments the ref count before returning
 122  * the vfsmount struct.
 123  */
 124 struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
 125 {
 126         struct vfsmount *child_mnt;
 127         spin_lock(&vfsmount_lock);
 128         if ((child_mnt = __lookup_mnt(mnt, dentry, 1)))
 129                 mntget(child_mnt);
 130         spin_unlock(&vfsmount_lock);
 131         return child_mnt;
 132 }
 133
 134 static inline int check_mnt(struct vfsmount *mnt)
 135 {
 136         return mnt->mnt_ns == current->nsproxy->mnt_ns;
 137 }
 138
 139 static void touch_mnt_namespace(struct mnt_namespace *ns)
 140 {
 141         if (ns) {
 142                 ns->event = ++event;
 143                 wake_up_interruptible(&ns->poll);
 144         }
 145 }
 146
 147 static void __touch_mnt_namespace(struct mnt_namespace *ns)
 148 {
 149         if (ns && ns->event != event) {
 150                 ns->event = event;
 151                 wake_up_interruptible(&ns->poll);
 152         }
 153 }
 154
 155 static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
 156 {
 157         old_nd->dentry = mnt->mnt_mountpoint;
 158         old_nd->mnt = mnt->mnt_parent;
 159         mnt->mnt_parent = mnt;
 160         mnt->mnt_mountpoint = mnt->mnt_root;
 161         list_del_init(&mnt->mnt_child);
 162         list_del_init(&mnt->mnt_hash);
 163         old_nd->dentry->d_mounted--;
 164 }
 165
 166 void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
 167                         struct vfsmount *child_mnt)
 168 {
 169         child_mnt->mnt_parent = mntget(mnt);
 170         child_mnt->mnt_mountpoint = dget(dentry);
 171         dentry->d_mounted++;
 172 }
 173
 174 static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
 175 {
 176         mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
 177         list_add_tail(&mnt->mnt_hash, mount_hashtable +
 178                         hash(nd->mnt, nd->dentry));
 179         list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
 180 }
 181
 182 /*
 183  * the caller must hold vfsmount_lock
 184  */
 185 static void commit_tree(struct vfsmount *mnt)
 186 {
 187         struct vfsmount *parent = mnt->mnt_parent;
 188         struct vfsmount *m;
 189         LIST_HEAD(head);
 190         struct mnt_namespace *n = parent->mnt_ns;
 191
 192         BUG_ON(parent == mnt);
 193
 194         list_add_tail(&head, &mnt->mnt_list);
 195         list_for_each_entry(m, &head, mnt_list)
 196                 m->mnt_ns = n;
 197         list_splice(&head, n->list.prev);
 198
 199         list_add_tail(&mnt->mnt_hash, mount_hashtable +
 200                                 hash(parent, mnt->mnt_mountpoint));
 201         list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 202         touch_mnt_namespace(n);
 203 }
 204
 205 static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
 206 {
 207         struct list_head *next = p->mnt_mounts.next;
 208         if (next == &p->mnt_mounts) {
 209                 while (1) {
 210                         if (p == root)
 211                                 return NULL;
 212                         next = p->mnt_child.next;
 213                         if (next != &p->mnt_parent->mnt_mounts)
 214                                 break;
 215                         p = p->mnt_parent;
 216                 }
 217         }
 218         return list_entry(next, struct vfsmount, mnt_child);
 219 }
 220
 221 static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
 222 {
 223         struct list_head *prev = p->mnt_mounts.prev;
 224         while (prev != &p->mnt_mounts) {
 225                 p = list_entry(prev, struct vfsmount, mnt_child);
 226                 prev = p->mnt_mounts.prev;
 227         }
 228         return p;
 229 }
 230
 231 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
 232                                         int flag)
 233 {
 234         struct super_block *sb = old->mnt_sb;
 235         struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
 236
 237         if (mnt) {
 238                 mnt->mnt_flags = old->mnt_flags;
 239                 atomic_inc(&sb->s_active);
 240                 mnt->mnt_sb = sb;
 241                 mnt->mnt_root = dget(root);
 242                 mnt->mnt_mountpoint = mnt->mnt_root;
 243                 mnt->mnt_parent = mnt;
 244
 245                 if (flag & CL_SLAVE) {
 246                         list_add(&mnt->mnt_slave, &old->mnt_slave_list);
 247                         mnt->mnt_master = old;
 248                         CLEAR_MNT_SHARED(mnt);
 249                 } else {
 250                         if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
 251                                 list_add(&mnt->mnt_share, &old->mnt_share);
 252                         if (IS_MNT_SLAVE(old))
 253                                 list_add(&mnt->mnt_slave, &old->mnt_slave);
 254                         mnt->mnt_master = old->mnt_master;
 255                 }
 256                 if (flag & CL_MAKE_SHARED)
 257                         set_mnt_shared(mnt);
 258
 259                 /* stick the duplicate mount on the same expiry list
 260                  * as the original if that was on one */
 261                 if (flag & CL_EXPIRE) {
 262                         spin_lock(&vfsmount_lock);
 263                         if (!list_empty(&old->mnt_expire))
 264                                 list_add(&mnt->mnt_expire, &old->mnt_expire);
 265                         spin_unlock(&vfsmount_lock);
 266                 }
 267         }
 268         return mnt;
 269 }
 270
 271 static inline void __mntput(struct vfsmount *mnt)
 272 {
 273         struct super_block *sb = mnt->mnt_sb;
 274         dput(mnt->mnt_root);
 275         free_vfsmnt(mnt);
 276         deactivate_super(sb);
 277 }
 278
 279 void mntput_no_expire(struct vfsmount *mnt)
 280 {
 281 repeat:
 282         if (atomic_dec_and_lock(&mnt->mnt_count, &vfsmount_lock)) {
 283                 if (likely(!mnt->mnt_pinned)) {
 284                         spin_unlock(&vfsmount_lock);
 285                         __mntput(mnt);
 286                         return;
 287                 }
 288                 atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
 289                 mnt->mnt_pinned = 0;
 290                 spin_unlock(&vfsmount_lock);
 291                 acct_auto_close_mnt(mnt);
 292                 security_sb_umount_close(mnt);
 293                 goto repeat;
 294         }
 295 }
 296
 297 EXPORT_SYMBOL(mntput_no_expire);
 298
 299 void mnt_pin(struct vfsmount *mnt)
 300 {
 301         spin_lock(&vfsmount_lock);
 302         mnt->mnt_pinned++;
 303         spin_unlock(&vfsmount_lock);
 304 }
 305
 306 EXPORT_SYMBOL(mnt_pin);
 307
 308 void mnt_unpin(struct vfsmount *mnt)
 309 {
 310         spin_lock(&vfsmount_lock);
 311         if (mnt->mnt_pinned) {
 312                 atomic_inc(&mnt->mnt_count);
 313                 mnt->mnt_pinned--;
 314         }
 315         spin_unlock(&vfsmount_lock);
 316 }
 317
 318 EXPORT_SYMBOL(mnt_unpin);
 319
 320 /* iterator */
 321 static void *m_start(struct seq_file *m, loff_t *pos)
 322 {
 323         struct mnt_namespace *n = m->private;
 324
 325         down_read(&namespace_sem);
 326         return seq_list_start(&n->list, *pos);
 327 }
 328
 329 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
 330 {
 331         struct mnt_namespace *n = m->private;
 332
 333         return seq_list_next(v, &n->list, pos);
 334 }
 335
 336 static void m_stop(struct seq_file *m, void *v)
 337 {
 338         up_read(&namespace_sem);
 339 }
 340
 341 static inline void mangle(struct seq_file *m, const char *s)
 342 {
 343         seq_escape(m, s, " \t\n\\");
 344 }
 345
 346 static int show_vfsmnt(struct seq_file *m, void *v)
 347 {
 348         struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
 349         int err = 0;
 350         static struct proc_fs_info {
 351                 int flag;
 352                 char *str;
 353         } fs_info[] = {
 354                 { MS_SYNCHRONOUS, ",sync" },
 355                 { MS_DIRSYNC, ",dirsync" },
 356                 { MS_MANDLOCK, ",mand" },
 357                 { 0, NULL }
 358         };
 359         static struct proc_fs_info mnt_info[] = {
 360                 { MNT_NOSUID, ",nosuid" },
 361                 { MNT_NODEV, ",nodev" },
 362                 { MNT_NOEXEC, ",noexec" },
 363                 { MNT_NOATIME, ",noatime" },
 364                 { MNT_NODIRATIME, ",nodiratime" },
 365                 { MNT_RELATIME, ",relatime" },
 366                 { 0, NULL }
 367         };
 368         struct proc_fs_info *fs_infop;
 369
 370         mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
 371         seq_putc(m, ' ');
 372         seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
 373         seq_putc(m, ' ');
 374         mangle(m, mnt->mnt_sb->s_type->name);
 375         if (mnt->mnt_sb->s_subtype && mnt->mnt_sb->s_subtype[0]) {
 376                 seq_putc(m, '.');
 377                 mangle(m, mnt->mnt_sb->s_subtype);
 378         }
 379         seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
 380         for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
 381                 if (mnt->mnt_sb->s_flags & fs_infop->flag)
 382                         seq_puts(m, fs_infop->str);
 383         }
 384         for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
 385                 if (mnt->mnt_flags & fs_infop->flag)
 386                         seq_puts(m, fs_infop->str);
 387         }
 388         if (mnt->mnt_sb->s_op->show_options)
 389                 err = mnt->mnt_sb->s_op->show_options(m, mnt);
 390         seq_puts(m, " 0 0\n");
 391         return err;
 392 }
 393
 394 struct seq_operations mounts_op = {
 395         .start  = m_start,
 396         .next   = m_next,
 397         .stop   = m_stop,
 398         .show   = show_vfsmnt
 399 };
 400
 401 static int show_vfsstat(struct seq_file *m, void *v)
 402 {
 403         struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
 404         int err = 0;
 405
 406         /* device */
 407         if (mnt->mnt_devname) {
 408                 seq_puts(m, "device ");
 409                 mangle(m, mnt->mnt_devname);
 410         } else
 411                 seq_puts(m, "no device");
 412
 413         /* mount point */
 414         seq_puts(m, " mounted on ");
 415         seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
 416         seq_putc(m, ' ');
 417
 418         /* file system type */
 419         seq_puts(m, "with fstype ");
 420         mangle(m, mnt->mnt_sb->s_type->name);
 421
 422         /* optional statistics */
 423         if (mnt->mnt_sb->s_op->show_stats) {
 424                 seq_putc(m, ' ');
 425                 err = mnt->mnt_sb->s_op->show_stats(m, mnt);
 426         }
 427
 428         seq_putc(m, '\n');
 429         return err;
 430 }
 431
 432 struct seq_operations mountstats_op = {
 433         .start  = m_start,
 434         .next   = m_next,
 435         .stop   = m_stop,
 436         .show   = show_vfsstat,
 437 };
 438
 439 /**
 440  * may_umount_tree - check if a mount tree is busy
 441  * @mnt: root of mount tree
 442  *
 443  * This is called to check if a tree of mounts has any
 444  * open files, pwds, chroots or sub mounts that are
 445  * busy.
 446  */
 447 int may_umount_tree(struct vfsmount *mnt)
 448 {
 449         int actual_refs = 0;
 450         int minimum_refs = 0;
 451         struct vfsmount *p;
 452
 453         spin_lock(&vfsmount_lock);
 454         for (p = mnt; p; p = next_mnt(p, mnt)) {
 455                 actual_refs += atomic_read(&p->mnt_count);
 456                 minimum_refs += 2;
 457         }
 458         spin_unlock(&vfsmount_lock);
 459
 460         if (actual_refs > minimum_refs)
 461                 return 0;
 462
 463         return 1;
 464 }
 465
 466 EXPORT_SYMBOL(may_umount_tree);
 467
 468 /**
 469  * may_umount - check if a mount point is busy
 470  * @mnt: root of mount
 471  *
 472  * This is called to check if a mount point has any
 473  * open files, pwds, chroots or sub mounts. If the
 474  * mount has sub mounts this will return busy
 475  * regardless of whether the sub mounts are busy.
 476  *
 477  * Doesn't take quota and stuff into account. IOW, in some cases it will
 478  * give false negatives. The main reason why it's here is that we need
 479  * a non-destructive way to look for easily umountable filesystems.
 480  */
 481 int may_umount(struct vfsmount *mnt)
 482 {
 483         int ret = 1;
 484         spin_lock(&vfsmount_lock);
 485         if (propagate_mount_busy(mnt, 2))
 486                 ret = 0;
 487         spin_unlock(&vfsmount_lock);
 488         return ret;
 489 }
 490
 491 EXPORT_SYMBOL(may_umount);
 492
 493 void release_mounts(struct list_head *head)
 494 {
 495         struct vfsmount *mnt;
 496         while (!list_empty(head)) {
 497                 mnt = list_first_entry(head, struct vfsmount, mnt_hash);
 498                 list_del_init(&mnt->mnt_hash);
 499                 if (mnt->mnt_parent != mnt) {
 500                         struct dentry *dentry;
 501                         struct vfsmount *m;
 502                         spin_lock(&vfsmount_lock);
 503                         dentry = mnt->mnt_mountpoint;
 504                         m = mnt->mnt_parent;
 505                         mnt->mnt_mountpoint = mnt->mnt_root;
 506                         mnt->mnt_parent = mnt;
 507                         spin_unlock(&vfsmount_lock);
 508                         dput(dentry);
 509                         mntput(m);
 510                 }
 511                 mntput(mnt);
 512         }
 513 }
 514
 515 void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
 516 {
 517         struct vfsmount *p;
 518
 519         for (p = mnt; p; p = next_mnt(p, mnt))
 520                 list_move(&p->mnt_hash, kill);
 521
 522         if (propagate)
 523                 propagate_umount(kill);
 524
 525         list_for_each_entry(p, kill, mnt_hash) {
 526                 list_del_init(&p->mnt_expire);
 527                 list_del_init(&p->mnt_list);
 528                 __touch_mnt_namespace(p->mnt_ns);
 529                 p->mnt_ns = NULL;
 530                 list_del_init(&p->mnt_child);
 531                 if (p->mnt_parent != p)
 532                         p->mnt_mountpoint->d_mounted--;
 533                 change_mnt_propagation(p, MS_PRIVATE);
 534         }
 535 }
 536
 537 static int do_umount(struct vfsmount *mnt, int flags)
 538 {
 539         struct super_block *sb = mnt->mnt_sb;
 540         int retval;
 541         LIST_HEAD(umount_list);
 542
 543         retval = security_sb_umount(mnt, flags);
 544         if (retval)
 545                 return retval;
 546
 547         /*
 548          * Allow userspace to request a mountpoint be expired rather than
 549          * unmounting unconditionally. Unmount only happens if:
 550          *  (1) the mark is already set (the mark is cleared by mntput())
 551          *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
 552          */
 553         if (flags & MNT_EXPIRE) {
 554                 if (mnt == current->fs->rootmnt ||
 555                     flags & (MNT_FORCE | MNT_DETACH))
 556                         return -EINVAL;
 557
 558                 if (atomic_read(&mnt->mnt_count) != 2)
 559                         return -EBUSY;
 560
 561                 if (!xchg(&mnt->mnt_expiry_mark, 1))
 562                         return -EAGAIN;
 563         }
 564
 565         /*
 566          * If we may have to abort operations to get out of this
 567          * mount, and they will themselves hold resources we must
 568          * allow the fs to do things. In the Unix tradition of
 569          * 'Gee thats tricky lets do it in userspace' the umount_begin
 570          * might fail to complete on the first run through as other tasks
 571          * must return, and the like. Thats for the mount program to worry
 572          * about for the moment.
 573          */
 574
 575         lock_kernel();
 576         if (sb->s_op->umount_begin)
 577                 sb->s_op->umount_begin(mnt, flags);
 578         unlock_kernel();
 579
 580         /*
 581          * No sense to grab the lock for this test, but test itself looks
 582          * somewhat bogus. Suggestions for better replacement?
 583          * Ho-hum... In principle, we might treat that as umount + switch
 584          * to rootfs. GC would eventually take care of the old vfsmount.
 585          * Actually it makes sense, especially if rootfs would contain a
 586          * /reboot - static binary that would close all descriptors and
 587          * call reboot(9). Then init(8) could umount root and exec /reboot.
 588          */
 589         if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
 590                 /*
 591                  * Special case for "unmounting" root ...
 592                  * we just try to remount it readonly.
 593                  */
 594                 down_write(&sb->s_umount);
 595                 if (!(sb->s_flags & MS_RDONLY)) {
 596                         lock_kernel();
 597                         DQUOT_OFF(sb);
 598                         retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
 599                         unlock_kernel();
 600                 }
 601                 up_write(&sb->s_umount);
 602                 return retval;
 603         }
 604
 605         down_write(&namespace_sem);
 606         spin_lock(&vfsmount_lock);
 607         event++;
 608
 609         retval = -EBUSY;
 610         if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
 611                 if (!list_empty(&mnt->mnt_list))
 612                         umount_tree(mnt, 1, &umount_list);
 613                 retval = 0;
 614         }
 615         spin_unlock(&vfsmount_lock);
 616         if (retval)
 617                 security_sb_umount_busy(mnt);
 618         up_write(&namespace_sem);
 619         release_mounts(&umount_list);
 620         return retval;
 621 }
 622
 623 /*
 624  * Now umount can handle mount points as well as block devices.
 625  * This is important for filesystems which use unnamed block devices.
 626  *
 627  * We now support a flag for forced unmount like the other 'big iron'
 628  * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
 629  */
 630
 631 asmlinkage long sys_umount(char __user * name, int flags)
 632 {
 633         struct nameidata nd;
 634         int retval;
 635
 636         retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
 637         if (retval)
 638                 goto out;
 639         retval = -EINVAL;
 640         if (nd.dentry != nd.mnt->mnt_root)
 641                 goto dput_and_out;
 642         if (!check_mnt(nd.mnt))
 643                 goto dput_and_out;
 644
 645         retval = -EPERM;
 646         if (!capable(CAP_SYS_ADMIN))
 647                 goto dput_and_out;
 648
 649         retval = do_umount(nd.mnt, flags);
 650 dput_and_out:
 651         path_release_on_umount(&nd);
 652 out:
 653         return retval;
 654 }
 655
 656 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
 657
 658 /*
 659  *      The 2.0 compatible umount. No flags.
 660  */
 661 asmlinkage long sys_oldumount(char __user * name)
 662 {
 663         return sys_umount(name, 0);
 664 }
 665
 666 #endif
 667
 668 static int mount_is_safe(struct nameidata *nd)
 669 {
 670         if (capable(CAP_SYS_ADMIN))
 671                 return 0;
 672         return -EPERM;
 673 #ifdef notyet
 674         if (S_ISLNK(nd->dentry->d_inode->i_mode))
 675                 return -EPERM;
 676         if (nd->dentry->d_inode->i_mode & S_ISVTX) {
 677                 if (current->uid != nd->dentry->d_inode->i_uid)
 678                         return -EPERM;
 679         }
 680         if (vfs_permission(nd, MAY_WRITE))
 681                 return -EPERM;
 682         return 0;
 683 #endif
 684 }
 685
 686 static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
 687 {
 688         while (1) {
 689                 if (d == dentry)
 690                         return 1;
 691                 if (d == NULL || d == d->d_parent)
 692                         return 0;
 693                 d = d->d_parent;
 694         }
 695 }
 696
 697 struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
 698                                         int flag)
 699 {
 700         struct vfsmount *res, *p, *q, *r, *s;
 701         struct nameidata nd;
 702
 703         if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
 704                 return NULL;
 705
 706         res = q = clone_mnt(mnt, dentry, flag);
 707         if (!q)
 708                 goto Enomem;
 709         q->mnt_mountpoint = mnt->mnt_mountpoint;
 710
 711         p = mnt;
 712         list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
 713                 if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
 714                         continue;
 715
 716                 for (s = r; s; s = next_mnt(s, r)) {
 717                         if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
 718                                 s = skip_mnt_tree(s);
 719                                 continue;
 720                         }
 721                         while (p != s->mnt_parent) {
 722                                 p = p->mnt_parent;
 723                                 q = q->mnt_parent;
 724                         }
 725                         p = s;
 726                         nd.mnt = q;
 727                         nd.dentry = p->mnt_mountpoint;
 728                         q = clone_mnt(p, p->mnt_root, flag);
 729                         if (!q)
 730                                 goto Enomem;
 731                         spin_lock(&vfsmount_lock);
 732                         list_add_tail(&q->mnt_list, &res->mnt_list);
 733                         attach_mnt(q, &nd);
 734                         spin_unlock(&vfsmount_lock);
 735                 }
 736         }
 737         return res;
 738 Enomem:
 739         if (res) {
 740                 LIST_HEAD(umount_list);
 741                 spin_lock(&vfsmount_lock);
 742                 umount_tree(res, 0, &umount_list);
 743                 spin_unlock(&vfsmount_lock);
 744                 release_mounts(&umount_list);
 745         }
 746         return NULL;
 747 }
 748
 749 /*
 750  *  @source_mnt : mount tree to be attached
 751  *  @nd         : place the mount tree @source_mnt is attached
 752  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
 753  *                 store the parent mount and mountpoint dentry.
 754  *                 (done when source_mnt is moved)
 755  *
 756  *  NOTE: in the table below explains the semantics when a source mount
 757  *  of a given type is attached to a destination mount of a given type.
 758  * ---------------------------------------------------------------------------
 759  * |         BIND MOUNT OPERATION                                            |
 760  * |**************************************************************************
 761  * | source-->| shared        |       private  |       slave    | unbindable |
 762  * | dest     |               |                |                |            |
 763  * |   |      |               |                |                |            |
 764  * |   v      |               |                |                |            |
 765  * |**************************************************************************
 766  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
 767  * |          |               |                |                |            |
 768  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
 769  * ***************************************************************************
 770  * A bind operation clones the source mount and mounts the clone on the
 771  * destination mount.
 772  *
 773  * (++)  the cloned mount is propagated to all the mounts in the propagation
 774  *       tree of the destination mount and the cloned mount is added to
 775  *       the peer group of the source mount.
 776  * (+)   the cloned mount is created under the destination mount and is marked
 777  *       as shared. The cloned mount is added to the peer group of the source
 778  *       mount.
 779  * (+++) the mount is propagated to all the mounts in the propagation tree
 780  *       of the destination mount and the cloned mount is made slave
 781  *       of the same master as that of the source mount. The cloned mount
 782  *       is marked as 'shared and slave'.
 783  * (*)   the cloned mount is made a slave of the same master as that of the
 784  *       source mount.
 785  *
 786  * ---------------------------------------------------------------------------
 787  * |                    MOVE MOUNT OPERATION                                 |
 788  * |**************************************************************************
 789  * | source-->| shared        |       private  |       slave    | unbindable |
 790  * | dest     |               |                |                |            |
 791  * |   |      |               |                |                |            |
 792  * |   v      |               |                |                |            |
 793  * |**************************************************************************
 794  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
 795  * |          |               |                |                |            |
 796  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
 797  * ***************************************************************************
 798  *
 799  * (+)  the mount is moved to the destination. And is then propagated to
 800  *      all the mounts in the propagation tree of the destination mount.
 801  * (+*)  the mount is moved to the destination.
 802  * (+++)  the mount is moved to the destination and is then propagated to
 803  *      all the mounts belonging to the destination mount's propagation tree.
 804  *      the mount is marked as 'shared and slave'.
 805  * (*)  the mount continues to be a slave at the new location.
 806  *
 807  * if the source mount is a tree, the operations explained above is
 808  * applied to each mount in the tree.
 809  * Must be called without spinlocks held, since this function can sleep
 810  * in allocations.
 811  */
 812 static int attach_recursive_mnt(struct vfsmount *source_mnt,
 813                         struct nameidata *nd, struct nameidata *parent_nd)
 814 {
 815         LIST_HEAD(tree_list);
 816         struct vfsmount *dest_mnt = nd->mnt;
 817         struct dentry *dest_dentry = nd->dentry;
 818         struct vfsmount *child, *p;
 819
 820         if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
 821                 return -EINVAL;
 822
 823         if (IS_MNT_SHARED(dest_mnt)) {
 824                 for (p = source_mnt; p; p = next_mnt(p, source_mnt))
 825                         set_mnt_shared(p);
 826         }
 827
 828         spin_lock(&vfsmount_lock);
 829         if (parent_nd) {
 830                 detach_mnt(source_mnt, parent_nd);
 831                 attach_mnt(source_mnt, nd);
 832                 touch_mnt_namespace(current->nsproxy->mnt_ns);
 833         } else {
 834                 mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
 835                 commit_tree(source_mnt);
 836         }
 837
 838         list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
 839                 list_del_init(&child->mnt_hash);
 840                 commit_tree(child);
 841         }
 842         spin_unlock(&vfsmount_lock);
 843         return 0;
 844 }
 845
 846 static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
 847 {
 848         int err;
 849         if (mnt->mnt_sb->s_flags & MS_NOUSER)
 850                 return -EINVAL;
 851
 852         if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
 853               S_ISDIR(mnt->mnt_root->d_inode->i_mode))
 854                 return -ENOTDIR;
 855
 856         err = -ENOENT;
 857         mutex_lock(&nd->dentry->d_inode->i_mutex);
 858         if (IS_DEADDIR(nd->dentry->d_inode))
 859                 goto out_unlock;
 860
 861         err = security_sb_check_sb(mnt, nd);
 862         if (err)
 863                 goto out_unlock;
 864
 865         err = -ENOENT;
 866         if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
 867                 err = attach_recursive_mnt(mnt, nd, NULL);
 868 out_unlock:
 869         mutex_unlock(&nd->dentry->d_inode->i_mutex);
 870         if (!err)
 871                 security_sb_post_addmount(mnt, nd);
 872         return err;
 873 }
 874
 875 /*
 876  * recursively change the type of the mountpoint.
 877  */
 878 static int do_change_type(struct nameidata *nd, int flag)
 879 {
 880         struct vfsmount *m, *mnt = nd->mnt;
 881         int recurse = flag & MS_REC;
 882         int type = flag & ~MS_REC;
 883
 884         if (!capable(CAP_SYS_ADMIN))
 885                 return -EPERM;
 886
 887         if (nd->dentry != nd->mnt->mnt_root)
 888                 return -EINVAL;
 889
 890         down_write(&namespace_sem);
 891         spin_lock(&vfsmount_lock);
 892         for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
 893                 change_mnt_propagation(m, type);
 894         spin_unlock(&vfsmount_lock);
 895         up_write(&namespace_sem);
 896         return 0;
 897 }
 898
 899 /*
 900  * do loopback mount.
 901  */
 902 static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
 903 {
 904         struct nameidata old_nd;
 905         struct vfsmount *mnt = NULL;
 906         int err = mount_is_safe(nd);
 907         if (err)
 908                 return err;
 909         if (!old_name || !*old_name)
 910                 return -EINVAL;
 911         err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
 912         if (err)
 913                 return err;
 914
 915         down_write(&namespace_sem);
 916         err = -EINVAL;
 917         if (IS_MNT_UNBINDABLE(old_nd.mnt))
 918                 goto out;
 919
 920         if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
 921                 goto out;
 922
 923         err = -ENOMEM;
 924         if (recurse)
 925                 mnt = copy_tree(old_nd.mnt, old_nd.dentry, 0);
 926         else
 927                 mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);
 928
 929         if (!mnt)
 930                 goto out;
 931
 932         err = graft_tree(mnt, nd);
 933         if (err) {
 934                 LIST_HEAD(umount_list);
 935                 spin_lock(&vfsmount_lock);
 936                 umount_tree(mnt, 0, &umount_list);
 937                 spin_unlock(&vfsmount_lock);
 938                 release_mounts(&umount_list);
 939         }
 940
 941 out:
 942         up_write(&namespace_sem);
 943         path_release(&old_nd);
 944         return err;
 945 }
 946
 947 /*
 948  * change filesystem flags. dir should be a physical root of filesystem.
 949  * If you've mounted a non-root directory somewhere and want to do remount
 950  * on it - tough luck.
 951  */
 952 static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
 953                       void *data)
 954 {
 955         int err;
 956         struct super_block *sb = nd->mnt->mnt_sb;
 957
 958         if (!capable(CAP_SYS_ADMIN))
 959                 return -EPERM;
 960
 961         if (!check_mnt(nd->mnt))
 962                 return -EINVAL;
 963
 964         if (nd->dentry != nd->mnt->mnt_root)
 965                 return -EINVAL;
 966
 967         down_write(&sb->s_umount);
 968         err = do_remount_sb(sb, flags, data, 0);
 969         if (!err)
 970                 nd->mnt->mnt_flags = mnt_flags;
 971         up_write(&sb->s_umount);
 972         if (!err)
 973                 security_sb_post_remount(nd->mnt, flags, data);
 974         return err;
 975 }
 976
 977 static inline int tree_contains_unbindable(struct vfsmount *mnt)
 978 {
 979         struct vfsmount *p;
 980         for (p = mnt; p; p = next_mnt(p, mnt)) {
 981                 if (IS_MNT_UNBINDABLE(p))
 982                         return 1;
 983         }
 984         return 0;
 985 }
 986
 987 static int do_move_mount(struct nameidata *nd, char *old_name)
 988 {
 989         struct nameidata old_nd, parent_nd;
 990         struct vfsmount *p;
 991         int err = 0;
 992         if (!capable(CAP_SYS_ADMIN))
 993                 return -EPERM;
 994         if (!old_name || !*old_name)
 995                 return -EINVAL;
 996         err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
 997         if (err)
 998                 return err;
 999
1000         down_write(&namespace_sem);
1001         while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
1002                 ;
1003         err = -EINVAL;
1004         if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
1005                 goto out;
1006
1007         err = -ENOENT;
1008         mutex_lock(&nd->dentry->d_inode->i_mutex);
1009         if (IS_DEADDIR(nd->dentry->d_inode))
1010                 goto out1;
1011
1012         if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
1013                 goto out1;
1014
1015         err = -EINVAL;
1016         if (old_nd.dentry != old_nd.mnt->mnt_root)
1017                 goto out1;
1018
1019         if (old_nd.mnt == old_nd.mnt->mnt_parent)
1020                 goto out1;
1021
1022         if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
1023               S_ISDIR(old_nd.dentry->d_inode->i_mode))
1024                 goto out1;
1025         /*
1026          * Don't move a mount residing in a shared parent.
1027          */
1028         if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
1029                 goto out1;
1030         /*
1031          * Don't move a mount tree containing unbindable mounts to a destination
1032          * mount which is shared.
1033          */
1034         if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
1035                 goto out1;
1036         err = -ELOOP;
1037         for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
1038                 if (p == old_nd.mnt)
1039                         goto out1;
1040
1041         if ((err = attach_recursive_mnt(old_nd.mnt, nd, &parent_nd)))
1042                 goto out1;
1043
1044         spin_lock(&vfsmount_lock);
1045         /* if the mount is moved, it should no longer be expire
1046          * automatically */
1047         list_del_init(&old_nd.mnt->mnt_expire);
1048         spin_unlock(&vfsmount_lock);
1049 out1:
1050         mutex_unlock(&nd->dentry->d_inode->i_mutex);
1051 out:
1052         up_write(&namespace_sem);
1053         if (!err)
1054                 path_release(&parent_nd);
1055         path_release(&old_nd);
1056         return err;
1057 }
1058
1059 /*
1060  * create a new mount for userspace and request it to be added into the
1061  * namespace's tree
1062  */
1063 static int do_new_mount(struct nameidata *nd, char *type, int flags,
1064                         int mnt_flags, char *name, void *data)
1065 {
1066         struct vfsmount *mnt;
1067
1068         if (!type || !memchr(type, 0, PAGE_SIZE))
1069                 return -EINVAL;
1070
1071         /* we need capabilities... */
1072         if (!capable(CAP_SYS_ADMIN))
1073                 return -EPERM;
1074
1075         mnt = do_kern_mount(type, flags, name, data);
1076         if (IS_ERR(mnt))
1077                 return PTR_ERR(mnt);
1078
1079         return do_add_mount(mnt, nd, mnt_flags, NULL);
1080 }
1081
1082 /*
1083  * add a mount into a namespace's mount tree
1084  * - provide the option of adding the new mount to an expiration list
1085  */
1086 int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
1087                  int mnt_flags, struct list_head *fslist)
1088 {
1089         int err;
1090
1091         down_write(&namespace_sem);
1092         /* Something was mounted here while we slept */
1093         while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
1094                 ;
1095         err = -EINVAL;
1096         if (!check_mnt(nd->mnt))
1097                 goto unlock;
1098
1099         /* Refuse the same filesystem on the same mount point */
1100         err = -EBUSY;
1101         if (nd->mnt->mnt_sb == newmnt->mnt_sb &&
1102             nd->mnt->mnt_root == nd->dentry)
1103                 goto unlock;
1104
1105         err = -EINVAL;
1106         if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
1107                 goto unlock;
1108
1109         newmnt->mnt_flags = mnt_flags;
1110         if ((err = graft_tree(newmnt, nd)))
1111                 goto unlock;
1112
1113         if (fslist) {
1114                 /* add to the specified expiration list */
1115                 spin_lock(&vfsmount_lock);
1116                 list_add_tail(&newmnt->mnt_expire, fslist);
1117                 spin_unlock(&vfsmount_lock);
1118         }
1119         up_write(&namespace_sem);
1120         return 0;
1121
1122 unlock:
1123         up_write(&namespace_sem);
1124         mntput(newmnt);
1125         return err;
1126 }
1127
1128 EXPORT_SYMBOL_GPL(do_add_mount);
1129
1130 static void expire_mount(struct vfsmount *mnt, struct list_head *mounts,
1131                                 struct list_head *umounts)
1132 {
1133         spin_lock(&vfsmount_lock);
1134
1135         /*
1136          * Check if mount is still attached, if not, let whoever holds it deal
1137          * with the sucker
1138          */
1139         if (mnt->mnt_parent == mnt) {
1140                 spin_unlock(&vfsmount_lock);
1141                 return;
1142         }
1143
1144         /*
1145          * Check that it is still dead: the count should now be 2 - as
1146          * contributed by the vfsmount parent and the mntget above
1147          */
1148         if (!propagate_mount_busy(mnt, 2)) {
1149                 /* delete from the namespace */
1150                 touch_mnt_namespace(mnt->mnt_ns);
1151                 list_del_init(&mnt->mnt_list);
1152                 mnt->mnt_ns = NULL;
1153                 umount_tree(mnt, 1, umounts);
1154                 spin_unlock(&vfsmount_lock);
1155         } else {
1156                 /*
1157                  * Someone brought it back to life whilst we didn't have any
1158                  * locks held so return it to the expiration list
1159                  */
1160                 list_add_tail(&mnt->mnt_expire, mounts);
1161                 spin_unlock(&vfsmount_lock);
1162         }
1163 }
1164
1165 /*
1166  * go through the vfsmounts we've just consigned to the graveyard to
1167  * - check that they're still dead
1168  * - delete the vfsmount from the appropriate namespace under lock
1169  * - dispose of the corpse
1170  */
1171 static void expire_mount_list(struct list_head *graveyard, struct list_head *mounts)
1172 {
1173         struct mnt_namespace *ns;
1174         struct vfsmount *mnt;
1175
1176         while (!list_empty(graveyard)) {
1177                 LIST_HEAD(umounts);
1178                 mnt = list_first_entry(graveyard, struct vfsmount, mnt_expire);
1179                 list_del_init(&mnt->mnt_expire);
1180
1181                 /* don't do anything if the namespace is dead - all the
1182                  * vfsmounts from it are going away anyway */
1183                 ns = mnt->mnt_ns;
1184                 if (!ns || !ns->root)
1185                         continue;
1186                 get_mnt_ns(ns);
1187
1188                 spin_unlock(&vfsmount_lock);
1189                 down_write(&namespace_sem);
1190                 expire_mount(mnt, mounts, &umounts);
1191                 up_write(&namespace_sem);
1192                 release_mounts(&umounts);
1193                 mntput(mnt);
1194                 put_mnt_ns(ns);
1195                 spin_lock(&vfsmount_lock);
1196         }
1197 }
1198
1199 /*
1200  * process a list of expirable mountpoints with the intent of discarding any
1201  * mountpoints that aren't in use and haven't been touched since last we came
1202  * here
1203  */
1204 void mark_mounts_for_expiry(struct list_head *mounts)
1205 {
1206         struct vfsmount *mnt, *next;
1207         LIST_HEAD(graveyard);
1208
1209         if (list_empty(mounts))
1210                 return;
1211
1212         spin_lock(&vfsmount_lock);
1213
1214         /* extract from the expiration list every vfsmount that matches the
1215          * following criteria:
1216          * - only referenced by its parent vfsmount
1217          * - still marked for expiry (marked on the last call here; marks are
1218          *   cleared by mntput())
1219          */
1220         list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
1221                 if (!xchg(&mnt->mnt_expiry_mark, 1) ||
1222                     atomic_read(&mnt->mnt_count) != 1)
1223                         continue;
1224
1225                 mntget(mnt);
1226                 list_move(&mnt->mnt_expire, &graveyard);
1227         }
1228
1229         expire_mount_list(&graveyard, mounts);
1230
1231         spin_unlock(&vfsmount_lock);
1232 }
1233
1234 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
1235
1236 /*
1237  * Ripoff of 'select_parent()'
1238  *
1239  * search the list of submounts for a given mountpoint, and move any
1240  * shrinkable submounts to the 'graveyard' list.
1241  */
1242 static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
1243 {
1244         struct vfsmount *this_parent = parent;
1245         struct list_head *next;
1246         int found = 0;
1247
1248 repeat:
1249         next = this_parent->mnt_mounts.next;
1250 resume:
1251         while (next != &this_parent->mnt_mounts) {
1252                 struct list_head *tmp = next;
1253                 struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);
1254
1255                 next = tmp->next;
1256                 if (!(mnt->mnt_flags & MNT_SHRINKABLE))
1257                         continue;
1258                 /*
1259                  * Descend a level if the d_mounts list is non-empty.
1260                  */
1261                 if (!list_empty(&mnt->mnt_mounts)) {
1262                         this_parent = mnt;
1263                         goto repeat;
1264                 }
1265
1266                 if (!propagate_mount_busy(mnt, 1)) {
1267                         mntget(mnt);
1268                         list_move_tail(&mnt->mnt_expire, graveyard);
1269                         found++;
1270                 }
1271         }
1272         /*
1273          * All done at this level ... ascend and resume the search
1274          */
1275         if (this_parent != parent) {
1276                 next = this_parent->mnt_child.next;
1277                 this_parent = this_parent->mnt_parent;
1278                 goto resume;
1279         }
1280         return found;
1281 }
1282
1283 /*
1284  * process a list of expirable mountpoints with the intent of discarding any
1285  * submounts of a specific parent mountpoint
1286  */
1287 void shrink_submounts(struct vfsmount *mountpoint, struct list_head *mounts)
1288 {
1289         LIST_HEAD(graveyard);
1290         int found;
1291
1292         spin_lock(&vfsmount_lock);
1293
1294         /* extract submounts of 'mountpoint' from the expiration list */
1295         while ((found = select_submounts(mountpoint, &graveyard)) != 0)
1296                 expire_mount_list(&graveyard, mounts);
1297
1298         spin_unlock(&vfsmount_lock);
1299 }
1300
1301 EXPORT_SYMBOL_GPL(shrink_submounts);
1302
1303 /*
1304  * Some copy_from_user() implementations do not return the exact number of
1305  * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
1306  * Note that this function differs from copy_from_user() in that it will oops
1307  * on bad values of `to', rather than returning a short copy.
1308  */
1309 static long exact_copy_from_user(void *to, const void __user * from,
1310                                  unsigned long n)
1311 {
1312         char *t = to;
1313         const char __user *f = from;
1314         char c;
1315
1316         if (!access_ok(VERIFY_READ, from, n))
1317                 return n;
1318
1319         while (n) {
1320                 if (__get_user(c, f)) {
1321                         memset(t, 0, n);
1322                         break;
1323                 }
1324                 *t++ = c;
1325                 f++;
1326                 n--;
1327         }
1328         return n;
1329 }
1330
1331 int copy_mount_options(const void __user * data, unsigned long *where)
1332 {
1333         int i;
1334         unsigned long page;
1335         unsigned long size;
1336
1337         *where = 0;
1338         if (!data)
1339                 return 0;
1340
1341         if (!(page = __get_free_page(GFP_KERNEL)))
1342                 return -ENOMEM;
1343
1344         /* We only care that *some* data at the address the user
1345          * gave us is valid.  Just in case, we'll zero
1346          * the remainder of the page.
1347          */
1348         /* copy_from_user cannot cross TASK_SIZE ! */
1349         size = TASK_SIZE - (unsigned long)data;
1350         if (size > PAGE_SIZE)
1351                 size = PAGE_SIZE;
1352
1353         i = size - exact_copy_from_user((void *)page, data, size);
1354         if (!i) {
1355                 free_page(page);
1356                 return -EFAULT;
1357         }
1358         if (i != PAGE_SIZE)
1359                 memset((char *)page + i, 0, PAGE_SIZE - i);
1360         *where = page;
1361         return 0;
1362 }
1363
1364 /*
1365  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
1366  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
1367  *
1368  * data is a (void *) that can point to any structure up to
1369  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
1370  * information (or be NULL).
1371  *
1372  * Pre-0.97 versions of mount() didn't have a flags word.
1373  * When the flags word was introduced its top half was required
1374  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
1375  * Therefore, if this magic number is present, it carries no information
1376  * and must be discarded.
1377  */
1378 long do_mount(char *dev_name, char *dir_name, char *type_page,
1379                   unsigned long flags, void *data_page)
1380 {
1381         struct nameidata nd;
1382         int retval = 0;
1383         int mnt_flags = 0;
1384
1385         /* Discard magic */
1386         if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
1387                 flags &= ~MS_MGC_MSK;
1388
1389         /* Basic sanity checks */
1390
1391         if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
1392                 return -EINVAL;
1393         if (dev_name && !memchr(dev_name, 0, PAGE_SIZE))
1394                 return -EINVAL;
1395
1396         if (data_page)
1397                 ((char *)data_page)[PAGE_SIZE - 1] = 0;
1398
1399         /* Separate the per-mountpoint flags */
1400         if (flags & MS_NOSUID)
1401                 mnt_flags |= MNT_NOSUID;
1402         if (flags & MS_NODEV)
1403                 mnt_flags |= MNT_NODEV;
1404         if (flags & MS_NOEXEC)
1405                 mnt_flags |= MNT_NOEXEC;
1406         if (flags & MS_NOATIME)
1407                 mnt_flags |= MNT_NOATIME;
1408         if (flags & MS_NODIRATIME)
1409                 mnt_flags |= MNT_NODIRATIME;
1410         if (flags & MS_RELATIME)
1411                 mnt_flags |= MNT_RELATIME;
1412
1413         flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
1414                    MS_NOATIME | MS_NODIRATIME | MS_RELATIME);
1415
1416         /* ... and get the mountpoint */
1417         retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
1418         if (retval)
1419                 return retval;
1420
1421         retval = security_sb_mount(dev_name, &nd, type_page, flags, data_page);
1422         if (retval)
1423                 goto dput_out;
1424
1425         if (flags & MS_REMOUNT)
1426                 retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
1427                                     data_page);
1428         else if (flags & MS_BIND)
1429                 retval = do_loopback(&nd, dev_name, flags & MS_REC);
1430         else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1431                 retval = do_change_type(&nd, flags);
1432         else if (flags & MS_MOVE)
1433                 retval = do_move_mount(&nd, dev_name);
1434         else
1435                 retval = do_new_mount(&nd, type_page, flags, mnt_flags,
1436                                       dev_name, data_page);
1437 dput_out:
1438         path_release(&nd);
1439         return retval;
1440 }
1441
1442 /*
1443  * Allocate a new namespace structure and populate it with contents
1444  * copied from the namespace of the passed in task structure.
1445  */
1446 static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
1447                 struct fs_struct *fs)
1448 {
1449         struct mnt_namespace *new_ns;
1450         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
1451         struct vfsmount *p, *q;
1452
1453         new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
1454         if (!new_ns)
1455                 return ERR_PTR(-ENOMEM);
1456
1457         atomic_set(&new_ns->count, 1);
1458         INIT_LIST_HEAD(&new_ns->list);
1459         init_waitqueue_head(&new_ns->poll);
1460         new_ns->event = 0;
1461
1462         down_write(&namespace_sem);
1463         /* First pass: copy the tree topology */
1464         new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
1465                                         CL_COPY_ALL | CL_EXPIRE);
1466         if (!new_ns->root) {
1467                 up_write(&namespace_sem);
1468                 kfree(new_ns);
1469                 return ERR_PTR(-ENOMEM);;
1470         }
1471         spin_lock(&vfsmount_lock);
1472         list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
1473         spin_unlock(&vfsmount_lock);
1474
1475         /*
1476          * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
1477          * as belonging to new namespace.  We have already acquired a private
1478          * fs_struct, so tsk->fs->lock is not needed.
1479          */
1480         p = mnt_ns->root;
1481         q = new_ns->root;
1482         while (p) {
1483                 q->mnt_ns = new_ns;
1484                 if (fs) {
1485                         if (p == fs->rootmnt) {
1486                                 rootmnt = p;
1487                                 fs->rootmnt = mntget(q);
1488                         }
1489                         if (p == fs->pwdmnt) {
1490                                 pwdmnt = p;
1491                                 fs->pwdmnt = mntget(q);
1492                         }
1493                         if (p == fs->altrootmnt) {
1494                                 altrootmnt = p;
1495                                 fs->altrootmnt = mntget(q);
1496                         }
1497                 }
1498                 p = next_mnt(p, mnt_ns->root);
1499                 q = next_mnt(q, new_ns->root);
1500         }
1501         up_write(&namespace_sem);
1502
1503         if (rootmnt)
1504                 mntput(rootmnt);
1505         if (pwdmnt)
1506                 mntput(pwdmnt);
1507         if (altrootmnt)
1508                 mntput(altrootmnt);
1509
1510         return new_ns;
1511 }
1512
1513 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
1514                 struct fs_struct *new_fs)
1515 {
1516         struct mnt_namespace *new_ns;
1517
1518         BUG_ON(!ns);
1519         get_mnt_ns(ns);
1520
1521         if (!(flags & CLONE_NEWNS))
1522                 return ns;
1523
1524         new_ns = dup_mnt_ns(ns, new_fs);
1525
1526         put_mnt_ns(ns);
1527         return new_ns;
1528 }
1529
1530 asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,
1531                           char __user * type, unsigned long flags,
1532                           void __user * data)
1533 {
1534         int retval;
1535         unsigned long data_page;
1536         unsigned long type_page;
1537         unsigned long dev_page;
1538         char *dir_page;
1539
1540         retval = copy_mount_options(type, &type_page);
1541         if (retval < 0)
1542                 return retval;
1543
1544         dir_page = getname(dir_name);
1545         retval = PTR_ERR(dir_page);
1546         if (IS_ERR(dir_page))
1547                 goto out1;
1548
1549         retval = copy_mount_options(dev_name, &dev_page);
1550         if (retval < 0)
1551                 goto out2;
1552
1553         retval = copy_mount_options(data, &data_page);
1554         if (retval < 0)
1555                 goto out3;
1556
1557         lock_kernel();
1558         retval = do_mount((char *)dev_page, dir_page, (char *)type_page,
1559                           flags, (void *)data_page);
1560         unlock_kernel();
1561         free_page(data_page);
1562
1563 out3:
1564         free_page(dev_page);
1565 out2:
1566         putname(dir_page);
1567 out1:
1568         free_page(type_page);
1569         return retval;
1570 }
1571
1572 /*
1573  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
1574  * It can block. Requires the big lock held.
1575  */
1576 void set_fs_root(struct fs_struct *fs, struct vfsmount *mnt,
1577                  struct dentry *dentry)
1578 {
1579         struct dentry *old_root;
1580         struct vfsmount *old_rootmnt;
1581         write_lock(&fs->lock);
1582         old_root = fs->root;
1583         old_rootmnt = fs->rootmnt;
1584         fs->rootmnt = mntget(mnt);
1585         fs->root = dget(dentry);
1586         write_unlock(&fs->lock);
1587         if (old_root) {
1588                 dput(old_root);
1589                 mntput(old_rootmnt);
1590         }
1591 }
1592
1593 /*
1594  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
1595  * It can block. Requires the big lock held.
1596  */
1597 void set_fs_pwd(struct fs_struct *fs, struct vfsmount *mnt,
1598                 struct dentry *dentry)
1599 {
1600         struct dentry *old_pwd;
1601         struct vfsmount *old_pwdmnt;
1602
1603         write_lock(&fs->lock);
1604         old_pwd = fs->pwd;
1605         old_pwdmnt = fs->pwdmnt;
1606         fs->pwdmnt = mntget(mnt);
1607         fs->pwd = dget(dentry);
1608         write_unlock(&fs->lock);
1609
1610         if (old_pwd) {
1611                 dput(old_pwd);
1612                 mntput(old_pwdmnt);
1613         }
1614 }
1615
1616 static void chroot_fs_refs(struct nameidata *old_nd, struct nameidata *new_nd)
1617 {
1618         struct task_struct *g, *p;
1619         struct fs_struct *fs;
1620
1621         read_lock(&tasklist_lock);
1622         do_each_thread(g, p) {
1623                 task_lock(p);
1624                 fs = p->fs;
1625                 if (fs) {
1626                         atomic_inc(&fs->count);
1627                         task_unlock(p);
1628                         if (fs->root == old_nd->dentry
1629                             && fs->rootmnt == old_nd->mnt)
1630                                 set_fs_root(fs, new_nd->mnt, new_nd->dentry);
1631                         if (fs->pwd == old_nd->dentry
1632                             && fs->pwdmnt == old_nd->mnt)
1633                                 set_fs_pwd(fs, new_nd->mnt, new_nd->dentry);
1634                         put_fs_struct(fs);
1635                 } else
1636                         task_unlock(p);
1637         } while_each_thread(g, p);
1638         read_unlock(&tasklist_lock);
1639 }
1640
1641 /*
1642  * pivot_root Semantics:
1643  * Moves the root file system of the current process to the directory put_old,
1644  * makes new_root as the new root file system of the current process, and sets
1645  * root/cwd of all processes which had them on the current root to new_root.
1646  *
1647  * Restrictions:
1648  * The new_root and put_old must be directories, and  must not be on the
1649  * same file  system as the current process root. The put_old  must  be
1650  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
1651  * pointed to by put_old must yield the same directory as new_root. No other
1652  * file system may be mounted on put_old. After all, new_root is a mountpoint.
1653  *
1654  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
1655  * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
1656  * in this situation.
1657  *
1658  * Notes:
1659  *  - we don't move root/cwd if they are not at the root (reason: if something
1660  *    cared enough to change them, it's probably wrong to force them elsewhere)
1661  *  - it's okay to pick a root that isn't the root of a file system, e.g.
1662  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
1663  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
1664  *    first.
1665  */
1666 asmlinkage long sys_pivot_root(const char __user * new_root,
1667                                const char __user * put_old)
1668 {
1669         struct vfsmount *tmp;
1670         struct nameidata new_nd, old_nd, parent_nd, root_parent, user_nd;
1671         int error;
1672
1673         if (!capable(CAP_SYS_ADMIN))
1674                 return -EPERM;
1675
1676         lock_kernel();
1677
1678         error = __user_walk(new_root, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
1679                             &new_nd);
1680         if (error)
1681                 goto out0;
1682         error = -EINVAL;
1683         if (!check_mnt(new_nd.mnt))
1684                 goto out1;
1685
1686         error = __user_walk(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_nd);
1687         if (error)
1688                 goto out1;
1689
1690         error = security_sb_pivotroot(&old_nd, &new_nd);
1691         if (error) {
1692                 path_release(&old_nd);
1693                 goto out1;
1694         }
1695
1696         read_lock(&current->fs->lock);
1697         user_nd.mnt = mntget(current->fs->rootmnt);
1698         user_nd.dentry = dget(current->fs->root);
1699         read_unlock(&current->fs->lock);
1700         down_write(&namespace_sem);
1701         mutex_lock(&old_nd.dentry->d_inode->i_mutex);
1702         error = -EINVAL;
1703         if (IS_MNT_SHARED(old_nd.mnt) ||
1704                 IS_MNT_SHARED(new_nd.mnt->mnt_parent) ||
1705                 IS_MNT_SHARED(user_nd.mnt->mnt_parent))
1706                 goto out2;
1707         if (!check_mnt(user_nd.mnt))
1708                 goto out2;
1709         error = -ENOENT;
1710         if (IS_DEADDIR(new_nd.dentry->d_inode))
1711                 goto out2;
1712         if (d_unhashed(new_nd.dentry) && !IS_ROOT(new_nd.dentry))
1713                 goto out2;
1714         if (d_unhashed(old_nd.dentry) && !IS_ROOT(old_nd.dentry))
1715                 goto out2;
1716         error = -EBUSY;
1717         if (new_nd.mnt == user_nd.mnt || old_nd.mnt == user_nd.mnt)
1718                 goto out2; /* loop, on the same file system  */
1719         error = -EINVAL;
1720         if (user_nd.mnt->mnt_root != user_nd.dentry)
1721                 goto out2; /* not a mountpoint */
1722         if (user_nd.mnt->mnt_parent == user_nd.mnt)
1723                 goto out2; /* not attached */
1724         if (new_nd.mnt->mnt_root != new_nd.dentry)
1725                 goto out2; /* not a mountpoint */
1726         if (new_nd.mnt->mnt_parent == new_nd.mnt)
1727                 goto out2; /* not attached */
1728         tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
1729         spin_lock(&vfsmount_lock);
1730         if (tmp != new_nd.mnt) {
1731                 for (;;) {
1732                         if (tmp->mnt_parent == tmp)
1733                                 goto out3; /* already mounted on put_old */
1734                         if (tmp->mnt_parent == new_nd.mnt)
1735                                 break;
1736                         tmp = tmp->mnt_parent;
1737                 }
1738                 if (!is_subdir(tmp->mnt_mountpoint, new_nd.dentry))
1739                         goto out3;
1740         } else if (!is_subdir(old_nd.dentry, new_nd.dentry))
1741                 goto out3;
1742         detach_mnt(new_nd.mnt, &parent_nd);
1743         detach_mnt(user_nd.mnt, &root_parent);
1744         attach_mnt(user_nd.mnt, &old_nd);     /* mount old root on put_old */
1745         attach_mnt(new_nd.mnt, &root_parent); /* mount new_root on / */
1746         touch_mnt_namespace(current->nsproxy->mnt_ns);
1747         spin_unlock(&vfsmount_lock);
1748         chroot_fs_refs(&user_nd, &new_nd);
1749         security_sb_post_pivotroot(&user_nd, &new_nd);
1750         error = 0;
1751         path_release(&root_parent);
1752         path_release(&parent_nd);
1753 out2:
1754         mutex_unlock(&old_nd.dentry->d_inode->i_mutex);
1755         up_write(&namespace_sem);
1756         path_release(&user_nd);
1757         path_release(&old_nd);
1758 out1:
1759         path_release(&new_nd);
1760 out0:
1761         unlock_kernel();
1762         return error;
1763 out3:
1764         spin_unlock(&vfsmount_lock);
1765         goto out2;
1766 }
1767
1768 static void __init init_mount_tree(void)
1769 {
1770         struct vfsmount *mnt;
1771         struct mnt_namespace *ns;
1772
1773         mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
1774         if (IS_ERR(mnt))
1775                 panic("Can't create rootfs");
1776         ns = kmalloc(sizeof(*ns), GFP_KERNEL);
1777         if (!ns)
1778                 panic("Can't allocate initial namespace");
1779         atomic_set(&ns->count, 1);
1780         INIT_LIST_HEAD(&ns->list);
1781         init_waitqueue_head(&ns->poll);
1782         ns->event = 0;
1783         list_add(&mnt->mnt_list, &ns->list);
1784         ns->root = mnt;
1785         mnt->mnt_ns = ns;
1786
1787         init_task.nsproxy->mnt_ns = ns;
1788         get_mnt_ns(ns);
1789
1790         set_fs_pwd(current->fs, ns->root, ns->root->mnt_root);
1791         set_fs_root(current->fs, ns->root, ns->root->mnt_root);
1792 }
1793
1794 void __init mnt_init(void)
1795 {
1796         struct list_head *d;
1797         unsigned int nr_hash;
1798         int i;
1799         int err;
1800
1801         init_rwsem(&namespace_sem);
1802
1803         mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
1804                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
1805
1806         mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
1807
1808         if (!mount_hashtable)
1809                 panic("Failed to allocate mount hash table\n");
1810
1811         /*
1812          * Find the power-of-two list-heads that can fit into the allocation..
1813          * We don't guarantee that "sizeof(struct list_head)" is necessarily
1814          * a power-of-two.
1815          */
1816         nr_hash = PAGE_SIZE / sizeof(struct list_head);
1817         hash_bits = 0;
1818         do {
1819                 hash_bits++;
1820         } while ((nr_hash >> hash_bits) != 0);
1821         hash_bits--;
1822
1823         /*
1824          * Re-calculate the actual number of entries and the mask
1825          * from the number of bits we can fit.
1826          */
1827         nr_hash = 1UL << hash_bits;
1828         hash_mask = nr_hash - 1;
1829
1830         printk("Mount-cache hash table entries: %d\n", nr_hash);
1831
1832         /* And initialize the newly allocated array */
1833         d = mount_hashtable;
1834         i = nr_hash;
1835         do {
1836                 INIT_LIST_HEAD(d);
1837                 d++;
1838                 i--;
1839         } while (i);
1840         err = sysfs_init();
1841         if (err)
1842                 printk(KERN_WARNING "%s: sysfs_init error: %d\n",
1843                         __FUNCTION__, err);
1844         err = subsystem_register(&fs_subsys);
1845         if (err)
1846                 printk(KERN_WARNING "%s: subsystem_register error: %d\n",
1847                         __FUNCTION__, err);
1848         init_rootfs();
1849         init_mount_tree();
1850 }
1851
1852 void __put_mnt_ns(struct mnt_namespace *ns)
1853 {
1854         struct vfsmount *root = ns->root;
1855         LIST_HEAD(umount_list);
1856         ns->root = NULL;
1857         spin_unlock(&vfsmount_lock);
1858         down_write(&namespace_sem);
1859         spin_lock(&vfsmount_lock);
1860         umount_tree(root, 0, &umount_list);
1861         spin_unlock(&vfsmount_lock);
1862         up_write(&namespace_sem);
1863         release_mounts(&umount_list);
1864         kfree(ns);
1865 }