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