fs/overlayfs/inode.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/xattr.h>
  13 #include "overlayfs.h"
  14
  15 static int ovl_copy_up_truncate(struct dentry *dentry)
  16 {
  17         int err;
  18         struct dentry *parent;
  19         struct kstat stat;
  20         struct path lowerpath;
  21
  22         parent = dget_parent(dentry);
  23         err = ovl_copy_up(parent);
  24         if (err)
  25                 goto out_dput_parent;
  26
  27         ovl_path_lower(dentry, &lowerpath);
  28         err = vfs_getattr(&lowerpath, &stat);
  29         if (err)
  30                 goto out_dput_parent;
  31
  32         stat.size = 0;
  33         err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
  34
  35 out_dput_parent:
  36         dput(parent);
  37         return err;
  38 }
  39
  40 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  41 {
  42         int err;
  43         struct dentry *upperdentry;
  44         const struct cred *old_cred;
  45
  46         /*
  47          * Check for permissions before trying to copy-up.  This is redundant
  48          * since it will be rechecked later by ->setattr() on upper dentry.  But
  49          * without this, copy-up can be triggered by just about anybody.
  50          *
  51          * We don't initialize inode->size, which just means that
  52          * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
  53          * check for a swapfile (which this won't be anyway).
  54          */
  55         err = inode_change_ok(dentry->d_inode, attr);
  56         if (err)
  57                 return err;
  58
  59         err = ovl_want_write(dentry);
  60         if (err)
  61                 goto out;
  62
  63         if (attr->ia_valid & ATTR_SIZE) {
  64                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
  65
  66                 err = -ETXTBSY;
  67                 if (atomic_read(&realinode->i_writecount) < 0)
  68                         goto out_drop_write;
  69         }
  70
  71         err = ovl_copy_up(dentry);
  72         if (!err) {
  73                 struct inode *winode = NULL;
  74
  75                 upperdentry = ovl_dentry_upper(dentry);
  76
  77                 if (attr->ia_valid & ATTR_SIZE) {
  78                         winode = d_inode(upperdentry);
  79                         err = get_write_access(winode);
  80                         if (err)
  81                                 goto out_drop_write;
  82                 }
  83
  84                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  85                         attr->ia_valid &= ~ATTR_MODE;
  86
  87                 inode_lock(upperdentry->d_inode);
  88                 old_cred = ovl_override_creds(dentry->d_sb);
  89                 err = notify_change(upperdentry, attr, NULL);
  90                 revert_creds(old_cred);
  91                 if (!err)
  92                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  93                 inode_unlock(upperdentry->d_inode);
  94
  95                 if (winode)
  96                         put_write_access(winode);
  97         }
  98 out_drop_write:
  99         ovl_drop_write(dentry);
 100 out:
 101         return err;
 102 }
 103
 104 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
 105                          struct kstat *stat)
 106 {
 107         struct path realpath;
 108         const struct cred *old_cred;
 109         int err;
 110
 111         ovl_path_real(dentry, &realpath);
 112         old_cred = ovl_override_creds(dentry->d_sb);
 113         err = vfs_getattr(&realpath, stat);
 114         revert_creds(old_cred);
 115         return err;
 116 }
 117
 118 int ovl_permission(struct inode *inode, int mask)
 119 {
 120         bool is_upper;
 121         struct inode *realinode = ovl_inode_real(inode, &is_upper);
 122         const struct cred *old_cred;
 123         int err;
 124
 125         /* Careful in RCU walk mode */
 126         if (!realinode) {
 127                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 128                 return -ECHILD;
 129         }
 130
 131         /*
 132          * Check overlay inode with the creds of task and underlying inode
 133          * with creds of mounter
 134          */
 135         err = generic_permission(inode, mask);
 136         if (err)
 137                 return err;
 138
 139         old_cred = ovl_override_creds(inode->i_sb);
 140         if (!is_upper)
 141                 mask &= ~(MAY_WRITE | MAY_APPEND);
 142         err = inode_permission(realinode, mask);
 143         revert_creds(old_cred);
 144
 145         return err;
 146 }
 147
 148 static const char *ovl_get_link(struct dentry *dentry,
 149                                 struct inode *inode,
 150                                 struct delayed_call *done)
 151 {
 152         struct dentry *realdentry;
 153         struct inode *realinode;
 154         const struct cred *old_cred;
 155         const char *p;
 156
 157         if (!dentry)
 158                 return ERR_PTR(-ECHILD);
 159
 160         realdentry = ovl_dentry_real(dentry);
 161         realinode = realdentry->d_inode;
 162
 163         if (WARN_ON(!realinode->i_op->get_link))
 164                 return ERR_PTR(-EPERM);
 165
 166         old_cred = ovl_override_creds(dentry->d_sb);
 167         p = realinode->i_op->get_link(realdentry, realinode, done);
 168         revert_creds(old_cred);
 169         return p;
 170 }
 171
 172 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 173 {
 174         struct path realpath;
 175         struct inode *realinode;
 176         const struct cred *old_cred;
 177         int err;
 178
 179         ovl_path_real(dentry, &realpath);
 180         realinode = realpath.dentry->d_inode;
 181
 182         if (!realinode->i_op->readlink)
 183                 return -EINVAL;
 184
 185         old_cred = ovl_override_creds(dentry->d_sb);
 186         err = realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 187         revert_creds(old_cred);
 188         return err;
 189 }
 190
 191 static bool ovl_is_private_xattr(const char *name)
 192 {
 193         return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;
 194 }
 195
 196 int ovl_setxattr(struct dentry *dentry, struct inode *inode,
 197                  const char *name, const void *value,
 198                  size_t size, int flags)
 199 {
 200         int err;
 201         struct dentry *upperdentry;
 202         const struct cred *old_cred;
 203
 204         err = ovl_want_write(dentry);
 205         if (err)
 206                 goto out;
 207
 208         err = -EPERM;
 209         if (ovl_is_private_xattr(name))
 210                 goto out_drop_write;
 211
 212         err = ovl_copy_up(dentry);
 213         if (err)
 214                 goto out_drop_write;
 215
 216         upperdentry = ovl_dentry_upper(dentry);
 217         old_cred = ovl_override_creds(dentry->d_sb);
 218         err = vfs_setxattr(upperdentry, name, value, size, flags);
 219         revert_creds(old_cred);
 220
 221 out_drop_write:
 222         ovl_drop_write(dentry);
 223 out:
 224         return err;
 225 }
 226
 227 ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode,
 228                      const char *name, void *value, size_t size)
 229 {
 230         struct dentry *realdentry = ovl_dentry_real(dentry);
 231         ssize_t res;
 232         const struct cred *old_cred;
 233
 234         if (ovl_is_private_xattr(name))
 235                 return -ENODATA;
 236
 237         old_cred = ovl_override_creds(dentry->d_sb);
 238         res = vfs_getxattr(realdentry, name, value, size);
 239         revert_creds(old_cred);
 240         return res;
 241 }
 242
 243 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 244 {
 245         struct dentry *realdentry = ovl_dentry_real(dentry);
 246         ssize_t res;
 247         int off;
 248         const struct cred *old_cred;
 249
 250         old_cred = ovl_override_creds(dentry->d_sb);
 251         res = vfs_listxattr(realdentry, list, size);
 252         revert_creds(old_cred);
 253         if (res <= 0 || size == 0)
 254                 return res;
 255
 256         /* filter out private xattrs */
 257         for (off = 0; off < res;) {
 258                 char *s = list + off;
 259                 size_t slen = strlen(s) + 1;
 260
 261                 BUG_ON(off + slen > res);
 262
 263                 if (ovl_is_private_xattr(s)) {
 264                         res -= slen;
 265                         memmove(s, s + slen, res - off);
 266                 } else {
 267                         off += slen;
 268                 }
 269         }
 270
 271         return res;
 272 }
 273
 274 int ovl_removexattr(struct dentry *dentry, const char *name)
 275 {
 276         int err;
 277         struct path realpath;
 278         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 279         const struct cred *old_cred;
 280
 281         err = ovl_want_write(dentry);
 282         if (err)
 283                 goto out;
 284
 285         err = -ENODATA;
 286         if (ovl_is_private_xattr(name))
 287                 goto out_drop_write;
 288
 289         if (!OVL_TYPE_UPPER(type)) {
 290                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 291                 if (err < 0)
 292                         goto out_drop_write;
 293
 294                 err = ovl_copy_up(dentry);
 295                 if (err)
 296                         goto out_drop_write;
 297
 298                 ovl_path_upper(dentry, &realpath);
 299         }
 300
 301         old_cred = ovl_override_creds(dentry->d_sb);
 302         err = vfs_removexattr(realpath.dentry, name);
 303         revert_creds(old_cred);
 304 out_drop_write:
 305         ovl_drop_write(dentry);
 306 out:
 307         return err;
 308 }
 309
 310 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 311 {
 312         struct inode *realinode = ovl_inode_real(inode, NULL);
 313         const struct cred *old_cred;
 314         struct posix_acl *acl;
 315
 316         if (!IS_POSIXACL(realinode))
 317                 return NULL;
 318
 319         if (!realinode->i_op->get_acl)
 320                 return NULL;
 321
 322         old_cred = ovl_override_creds(inode->i_sb);
 323         acl = realinode->i_op->get_acl(realinode, type);
 324         revert_creds(old_cred);
 325
 326         return acl;
 327 }
 328
 329 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 330                                   struct dentry *realdentry)
 331 {
 332         if (OVL_TYPE_UPPER(type))
 333                 return false;
 334
 335         if (special_file(realdentry->d_inode->i_mode))
 336                 return false;
 337
 338         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 339                 return false;
 340
 341         return true;
 342 }
 343
 344 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 345 {
 346         int err = 0;
 347         struct path realpath;
 348         enum ovl_path_type type;
 349
 350         type = ovl_path_real(dentry, &realpath);
 351         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 352                 err = ovl_want_write(dentry);
 353                 if (!err) {
 354                         if (file_flags & O_TRUNC)
 355                                 err = ovl_copy_up_truncate(dentry);
 356                         else
 357                                 err = ovl_copy_up(dentry);
 358                         ovl_drop_write(dentry);
 359                 }
 360         }
 361
 362         return err;
 363 }
 364
 365 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 366 {
 367         struct dentry *alias;
 368         struct path upperpath;
 369
 370         if (!(flags & S_ATIME))
 371                 return 0;
 372
 373         alias = d_find_any_alias(inode);
 374         if (!alias)
 375                 return 0;
 376
 377         ovl_path_upper(alias, &upperpath);
 378         if (upperpath.dentry) {
 379                 touch_atime(&upperpath);
 380                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 381         }
 382
 383         dput(alias);
 384
 385         return 0;
 386 }
 387
 388 static const struct inode_operations ovl_file_inode_operations = {
 389         .setattr        = ovl_setattr,
 390         .permission     = ovl_permission,
 391         .getattr        = ovl_getattr,
 392         .setxattr       = ovl_setxattr,
 393         .getxattr       = ovl_getxattr,
 394         .listxattr      = ovl_listxattr,
 395         .removexattr    = ovl_removexattr,
 396         .get_acl        = ovl_get_acl,
 397         .update_time    = ovl_update_time,
 398 };
 399
 400 static const struct inode_operations ovl_symlink_inode_operations = {
 401         .setattr        = ovl_setattr,
 402         .get_link       = ovl_get_link,
 403         .readlink       = ovl_readlink,
 404         .getattr        = ovl_getattr,
 405         .setxattr       = ovl_setxattr,
 406         .getxattr       = ovl_getxattr,
 407         .listxattr      = ovl_listxattr,
 408         .removexattr    = ovl_removexattr,
 409         .update_time    = ovl_update_time,
 410 };
 411
 412 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 413 {
 414         struct inode *inode;
 415
 416         inode = new_inode(sb);
 417         if (!inode)
 418                 return NULL;
 419
 420         inode->i_ino = get_next_ino();
 421         inode->i_mode = mode;
 422         inode->i_flags |= S_NOCMTIME;
 423
 424         mode &= S_IFMT;
 425         switch (mode) {
 426         case S_IFDIR:
 427                 inode->i_op = &ovl_dir_inode_operations;
 428                 inode->i_fop = &ovl_dir_operations;
 429                 break;
 430
 431         case S_IFLNK:
 432                 inode->i_op = &ovl_symlink_inode_operations;
 433                 break;
 434
 435         case S_IFREG:
 436         case S_IFSOCK:
 437         case S_IFBLK:
 438         case S_IFCHR:
 439         case S_IFIFO:
 440                 inode->i_op = &ovl_file_inode_operations;
 441                 break;
 442
 443         default:
 444                 WARN(1, "illegal file type: %i\n", mode);
 445                 iput(inode);
 446                 inode = NULL;
 447         }
 448
 449         return inode;
 450 }