fs/overlayfs/copy_up.c

   1 /*
   2  *
   3  * Copyright (C) 2011 Novell Inc.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 as published by
   7  * the Free Software Foundation.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/fs.h>
  12 #include <linux/slab.h>
  13 #include <linux/file.h>
  14 #include <linux/splice.h>
  15 #include <linux/xattr.h>
  16 #include <linux/security.h>
  17 #include <linux/uaccess.h>
  18 #include <linux/sched.h>
  19 #include <linux/namei.h>
  20 #include <linux/fdtable.h>
  21 #include <linux/ratelimit.h>
  22 #include "overlayfs.h"
  23
  24 #define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
  25
  26 static bool __read_mostly ovl_check_copy_up;
  27 module_param_named(check_copy_up, ovl_check_copy_up, bool,
  28                    S_IWUSR | S_IRUGO);
  29 MODULE_PARM_DESC(ovl_check_copy_up,
  30                  "Warn on copy-up when causing process also has a R/O fd open");
  31
  32 static int ovl_check_fd(const void *data, struct file *f, unsigned int fd)
  33 {
  34         const struct dentry *dentry = data;
  35
  36         if (f->f_inode == d_inode(dentry))
  37                 pr_warn_ratelimited("overlayfs: Warning: Copying up %pD, but open R/O on fd %u which will cease to be coherent [pid=%d %s]\n",
  38                                     f, fd, current->pid, current->comm);
  39         return 0;
  40 }
  41
  42 /*
  43  * Check the fds open by this process and warn if something like the following
  44  * scenario is about to occur:
  45  *
  46  *      fd1 = open("foo", O_RDONLY);
  47  *      fd2 = open("foo", O_RDWR);
  48  */
  49 static void ovl_do_check_copy_up(struct dentry *dentry)
  50 {
  51         if (ovl_check_copy_up)
  52                 iterate_fd(current->files, 0, ovl_check_fd, dentry);
  53 }
  54
  55 int ovl_copy_xattr(struct dentry *old, struct dentry *new)
  56 {
  57         ssize_t list_size, size, value_size = 0;
  58         char *buf, *name, *value = NULL;
  59         int uninitialized_var(error);
  60
  61         if (!old->d_inode->i_op->getxattr ||
  62             !new->d_inode->i_op->getxattr)
  63                 return 0;
  64
  65         list_size = vfs_listxattr(old, NULL, 0);
  66         if (list_size <= 0) {
  67                 if (list_size == -EOPNOTSUPP)
  68                         return 0;
  69                 return list_size;
  70         }
  71
  72         buf = kzalloc(list_size, GFP_KERNEL);
  73         if (!buf)
  74                 return -ENOMEM;
  75
  76         list_size = vfs_listxattr(old, buf, list_size);
  77         if (list_size <= 0) {
  78                 error = list_size;
  79                 goto out;
  80         }
  81
  82         for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
  83                 if (ovl_is_private_xattr(name))
  84                         continue;
  85 retry:
  86                 size = vfs_getxattr(old, name, value, value_size);
  87                 if (size == -ERANGE)
  88                         size = vfs_getxattr(old, name, NULL, 0);
  89
  90                 if (size < 0) {
  91                         error = size;
  92                         break;
  93                 }
  94
  95                 if (size > value_size) {
  96                         void *new;
  97
  98                         new = krealloc(value, size, GFP_KERNEL);
  99                         if (!new) {
 100                                 error = -ENOMEM;
 101                                 break;
 102                         }
 103                         value = new;
 104                         value_size = size;
 105                         goto retry;
 106                 }
 107
 108                 error = security_inode_copy_up_xattr(name);
 109                 if (error < 0 && error != -EOPNOTSUPP)
 110                         break;
 111                 if (error == 1) {
 112                         error = 0;
 113                         continue; /* Discard */
 114                 }
 115                 error = vfs_setxattr(new, name, value, size, 0);
 116                 if (error)
 117                         break;
 118         }
 119         kfree(value);
 120 out:
 121         kfree(buf);
 122         return error;
 123 }
 124
 125 static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
 126 {
 127         struct file *old_file;
 128         struct file *new_file;
 129         loff_t old_pos = 0;
 130         loff_t new_pos = 0;
 131         int error = 0;
 132
 133         if (len == 0)
 134                 return 0;
 135
 136         old_file = ovl_path_open(old, O_LARGEFILE | O_RDONLY);
 137         if (IS_ERR(old_file))
 138                 return PTR_ERR(old_file);
 139
 140         new_file = ovl_path_open(new, O_LARGEFILE | O_WRONLY);
 141         if (IS_ERR(new_file)) {
 142                 error = PTR_ERR(new_file);
 143                 goto out_fput;
 144         }
 145
 146         /* FIXME: copy up sparse files efficiently */
 147         while (len) {
 148                 size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
 149                 long bytes;
 150
 151                 if (len < this_len)
 152                         this_len = len;
 153
 154                 if (signal_pending_state(TASK_KILLABLE, current)) {
 155                         error = -EINTR;
 156                         break;
 157                 }
 158
 159                 bytes = do_splice_direct(old_file, &old_pos,
 160                                          new_file, &new_pos,
 161                                          this_len, SPLICE_F_MOVE);
 162                 if (bytes <= 0) {
 163                         error = bytes;
 164                         break;
 165                 }
 166                 WARN_ON(old_pos != new_pos);
 167
 168                 len -= bytes;
 169         }
 170
 171         fput(new_file);
 172 out_fput:
 173         fput(old_file);
 174         return error;
 175 }
 176
 177 static char *ovl_read_symlink(struct dentry *realdentry)
 178 {
 179         int res;
 180         char *buf;
 181         struct inode *inode = realdentry->d_inode;
 182         mm_segment_t old_fs;
 183
 184         res = -EINVAL;
 185         if (!inode->i_op->readlink)
 186                 goto err;
 187
 188         res = -ENOMEM;
 189         buf = (char *) __get_free_page(GFP_KERNEL);
 190         if (!buf)
 191                 goto err;
 192
 193         old_fs = get_fs();
 194         set_fs(get_ds());
 195         /* The cast to a user pointer is valid due to the set_fs() */
 196         res = inode->i_op->readlink(realdentry,
 197                                     (char __user *)buf, PAGE_SIZE - 1);
 198         set_fs(old_fs);
 199         if (res < 0) {
 200                 free_page((unsigned long) buf);
 201                 goto err;
 202         }
 203         buf[res] = '\0';
 204
 205         return buf;
 206
 207 err:
 208         return ERR_PTR(res);
 209 }
 210
 211 static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
 212 {
 213         struct iattr attr = {
 214                 .ia_valid =
 215                      ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
 216                 .ia_atime = stat->atime,
 217                 .ia_mtime = stat->mtime,
 218         };
 219
 220         return notify_change(upperdentry, &attr, NULL);
 221 }
 222
 223 int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
 224 {
 225         int err = 0;
 226
 227         if (!S_ISLNK(stat->mode)) {
 228                 struct iattr attr = {
 229                         .ia_valid = ATTR_MODE,
 230                         .ia_mode = stat->mode,
 231                 };
 232                 err = notify_change(upperdentry, &attr, NULL);
 233         }
 234         if (!err) {
 235                 struct iattr attr = {
 236                         .ia_valid = ATTR_UID | ATTR_GID,
 237                         .ia_uid = stat->uid,
 238                         .ia_gid = stat->gid,
 239                 };
 240                 err = notify_change(upperdentry, &attr, NULL);
 241         }
 242         if (!err)
 243                 ovl_set_timestamps(upperdentry, stat);
 244
 245         return err;
 246 }
 247
 248 static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
 249                               struct dentry *dentry, struct path *lowerpath,
 250                               struct kstat *stat, const char *link)
 251 {
 252         struct inode *wdir = workdir->d_inode;
 253         struct inode *udir = upperdir->d_inode;
 254         struct dentry *newdentry = NULL;
 255         struct dentry *upper = NULL;
 256         umode_t mode = stat->mode;
 257         int err;
 258         const struct cred *old_creds = NULL;
 259         struct cred *new_creds = NULL;
 260
 261         newdentry = ovl_lookup_temp(workdir, dentry);
 262         err = PTR_ERR(newdentry);
 263         if (IS_ERR(newdentry))
 264                 goto out;
 265
 266         upper = lookup_one_len(dentry->d_name.name, upperdir,
 267                                dentry->d_name.len);
 268         err = PTR_ERR(upper);
 269         if (IS_ERR(upper))
 270                 goto out1;
 271
 272         err = security_inode_copy_up(dentry, &new_creds);
 273         if (err < 0)
 274                 goto out2;
 275
 276         if (new_creds)
 277                 old_creds = override_creds(new_creds);
 278
 279         /* Can't properly set mode on creation because of the umask */
 280         stat->mode &= S_IFMT;
 281         err = ovl_create_real(wdir, newdentry, stat, link, NULL, true);
 282         stat->mode = mode;
 283
 284         if (new_creds) {
 285                 revert_creds(old_creds);
 286                 put_cred(new_creds);
 287         }
 288
 289         if (err)
 290                 goto out2;
 291
 292         if (S_ISREG(stat->mode)) {
 293                 struct path upperpath;
 294
 295                 ovl_path_upper(dentry, &upperpath);
 296                 BUG_ON(upperpath.dentry != NULL);
 297                 upperpath.dentry = newdentry;
 298
 299                 err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
 300                 if (err)
 301                         goto out_cleanup;
 302         }
 303
 304         err = ovl_copy_xattr(lowerpath->dentry, newdentry);
 305         if (err)
 306                 goto out_cleanup;
 307
 308         inode_lock(newdentry->d_inode);
 309         err = ovl_set_attr(newdentry, stat);
 310         inode_unlock(newdentry->d_inode);
 311         if (err)
 312                 goto out_cleanup;
 313
 314         err = ovl_do_rename(wdir, newdentry, udir, upper, 0);
 315         if (err)
 316                 goto out_cleanup;
 317
 318         ovl_dentry_update(dentry, newdentry);
 319         ovl_inode_update(d_inode(dentry), d_inode(newdentry));
 320         newdentry = NULL;
 321
 322         /*
 323          * Non-directores become opaque when copied up.
 324          */
 325         if (!S_ISDIR(stat->mode))
 326                 ovl_dentry_set_opaque(dentry, true);
 327 out2:
 328         dput(upper);
 329 out1:
 330         dput(newdentry);
 331 out:
 332         return err;
 333
 334 out_cleanup:
 335         ovl_cleanup(wdir, newdentry);
 336         goto out2;
 337 }
 338
 339 /*
 340  * Copy up a single dentry
 341  *
 342  * Directory renames only allowed on "pure upper" (already created on
 343  * upper filesystem, never copied up).  Directories which are on lower or
 344  * are merged may not be renamed.  For these -EXDEV is returned and
 345  * userspace has to deal with it.  This means, when copying up a
 346  * directory we can rely on it and ancestors being stable.
 347  *
 348  * Non-directory renames start with copy up of source if necessary.  The
 349  * actual rename will only proceed once the copy up was successful.  Copy
 350  * up uses upper parent i_mutex for exclusion.  Since rename can change
 351  * d_parent it is possible that the copy up will lock the old parent.  At
 352  * that point the file will have already been copied up anyway.
 353  */
 354 int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 355                     struct path *lowerpath, struct kstat *stat)
 356 {
 357         struct dentry *workdir = ovl_workdir(dentry);
 358         int err;
 359         struct kstat pstat;
 360         struct path parentpath;
 361         struct dentry *upperdir;
 362         struct dentry *upperdentry;
 363         const struct cred *old_cred;
 364         char *link = NULL;
 365
 366         if (WARN_ON(!workdir))
 367                 return -EROFS;
 368
 369         ovl_do_check_copy_up(lowerpath->dentry);
 370
 371         ovl_path_upper(parent, &parentpath);
 372         upperdir = parentpath.dentry;
 373
 374         err = vfs_getattr(&parentpath, &pstat);
 375         if (err)
 376                 return err;
 377
 378         if (S_ISLNK(stat->mode)) {
 379                 link = ovl_read_symlink(lowerpath->dentry);
 380                 if (IS_ERR(link))
 381                         return PTR_ERR(link);
 382         }
 383
 384         old_cred = ovl_override_creds(dentry->d_sb);
 385
 386         err = -EIO;
 387         if (lock_rename(workdir, upperdir) != NULL) {
 388                 pr_err("overlayfs: failed to lock workdir+upperdir\n");
 389                 goto out_unlock;
 390         }
 391         upperdentry = ovl_dentry_upper(dentry);
 392         if (upperdentry) {
 393                 /* Raced with another copy-up?  Nothing to do, then... */
 394                 err = 0;
 395                 goto out_unlock;
 396         }
 397
 398         err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
 399                                  stat, link);
 400         if (!err) {
 401                 /* Restore timestamps on parent (best effort) */
 402                 ovl_set_timestamps(upperdir, &pstat);
 403         }
 404 out_unlock:
 405         unlock_rename(workdir, upperdir);
 406         revert_creds(old_cred);
 407
 408         if (link)
 409                 free_page((unsigned long) link);
 410
 411         return err;
 412 }
 413
 414 int ovl_copy_up(struct dentry *dentry)
 415 {
 416         int err;
 417
 418         err = 0;
 419         while (!err) {
 420                 struct dentry *next;
 421                 struct dentry *parent;
 422                 struct path lowerpath;
 423                 struct kstat stat;
 424                 enum ovl_path_type type = ovl_path_type(dentry);
 425
 426                 if (OVL_TYPE_UPPER(type))
 427                         break;
 428
 429                 next = dget(dentry);
 430                 /* find the topmost dentry not yet copied up */
 431                 for (;;) {
 432                         parent = dget_parent(next);
 433
 434                         type = ovl_path_type(parent);
 435                         if (OVL_TYPE_UPPER(type))
 436                                 break;
 437
 438                         dput(next);
 439                         next = parent;
 440                 }
 441
 442                 ovl_path_lower(next, &lowerpath);
 443                 err = vfs_getattr(&lowerpath, &stat);
 444                 if (!err)
 445                         err = ovl_copy_up_one(parent, next, &lowerpath, &stat);
 446
 447                 dput(parent);
 448                 dput(next);
 449         }
 450
 451         return err;
 452 }