| 1 | // SPDX-License-Identifier: GPL-2.0 |
| 2 | /* |
| 3 | * linux/fs/attr.c |
| 4 | * |
| 5 | * Copyright (C) 1991, 1992 Linus Torvalds |
| 6 | * changes by Thomas Schoebel-Theuer |
| 7 | */ |
| 8 | |
| 9 | #include <linux/export.h> |
| 10 | #include <linux/time.h> |
| 11 | #include <linux/mm.h> |
| 12 | #include <linux/string.h> |
| 13 | #include <linux/sched/signal.h> |
| 14 | #include <linux/capability.h> |
| 15 | #include <linux/fsnotify.h> |
| 16 | #include <linux/fcntl.h> |
| 17 | #include <linux/filelock.h> |
| 18 | #include <linux/security.h> |
| 19 | #include <linux/evm.h> |
| 20 | #include <linux/ima.h> |
| 21 | |
| 22 | #include "internal.h" |
| 23 | |
| 24 | /** |
| 25 | * setattr_should_drop_sgid - determine whether the setgid bit needs to be |
| 26 | * removed |
| 27 | * @idmap: idmap of the mount @inode was found from |
| 28 | * @inode: inode to check |
| 29 | * |
| 30 | * This function determines whether the setgid bit needs to be removed. |
| 31 | * We retain backwards compatibility and require setgid bit to be removed |
| 32 | * unconditionally if S_IXGRP is set. Otherwise we have the exact same |
| 33 | * requirements as setattr_prepare() and setattr_copy(). |
| 34 | * |
| 35 | * Return: ATTR_KILL_SGID if setgid bit needs to be removed, 0 otherwise. |
| 36 | */ |
| 37 | int setattr_should_drop_sgid(struct mnt_idmap *idmap, |
| 38 | const struct inode *inode) |
| 39 | { |
| 40 | umode_t mode = inode->i_mode; |
| 41 | |
| 42 | if (!(mode & S_ISGID)) |
| 43 | return 0; |
| 44 | if (mode & S_IXGRP) |
| 45 | return ATTR_KILL_SGID; |
| 46 | if (!in_group_or_capable(idmap, inode, i_gid_into_vfsgid(idmap, inode))) |
| 47 | return ATTR_KILL_SGID; |
| 48 | return 0; |
| 49 | } |
| 50 | EXPORT_SYMBOL(setattr_should_drop_sgid); |
| 51 | |
| 52 | /** |
| 53 | * setattr_should_drop_suidgid - determine whether the set{g,u}id bit needs to |
| 54 | * be dropped |
| 55 | * @idmap: idmap of the mount @inode was found from |
| 56 | * @inode: inode to check |
| 57 | * |
| 58 | * This function determines whether the set{g,u}id bits need to be removed. |
| 59 | * If the setuid bit needs to be removed ATTR_KILL_SUID is returned. If the |
| 60 | * setgid bit needs to be removed ATTR_KILL_SGID is returned. If both |
| 61 | * set{g,u}id bits need to be removed the corresponding mask of both flags is |
| 62 | * returned. |
| 63 | * |
| 64 | * Return: A mask of ATTR_KILL_S{G,U}ID indicating which - if any - setid bits |
| 65 | * to remove, 0 otherwise. |
| 66 | */ |
| 67 | int setattr_should_drop_suidgid(struct mnt_idmap *idmap, |
| 68 | struct inode *inode) |
| 69 | { |
| 70 | umode_t mode = inode->i_mode; |
| 71 | int kill = 0; |
| 72 | |
| 73 | /* suid always must be killed */ |
| 74 | if (unlikely(mode & S_ISUID)) |
| 75 | kill = ATTR_KILL_SUID; |
| 76 | |
| 77 | kill |= setattr_should_drop_sgid(idmap, inode); |
| 78 | |
| 79 | if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode))) |
| 80 | return kill; |
| 81 | |
| 82 | return 0; |
| 83 | } |
| 84 | EXPORT_SYMBOL(setattr_should_drop_suidgid); |
| 85 | |
| 86 | /** |
| 87 | * chown_ok - verify permissions to chown inode |
| 88 | * @idmap: idmap of the mount @inode was found from |
| 89 | * @inode: inode to check permissions on |
| 90 | * @ia_vfsuid: uid to chown @inode to |
| 91 | * |
| 92 | * If the inode has been found through an idmapped mount the idmap of |
| 93 | * the vfsmount must be passed through @idmap. This function will then |
| 94 | * take care to map the inode according to @idmap before checking |
| 95 | * permissions. On non-idmapped mounts or if permission checking is to be |
| 96 | * performed on the raw inode simply pass @nop_mnt_idmap. |
| 97 | */ |
| 98 | static bool chown_ok(struct mnt_idmap *idmap, |
| 99 | const struct inode *inode, vfsuid_t ia_vfsuid) |
| 100 | { |
| 101 | vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode); |
| 102 | if (vfsuid_eq_kuid(vfsuid, current_fsuid()) && |
| 103 | vfsuid_eq(ia_vfsuid, vfsuid)) |
| 104 | return true; |
| 105 | if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN)) |
| 106 | return true; |
| 107 | if (!vfsuid_valid(vfsuid) && |
| 108 | ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN)) |
| 109 | return true; |
| 110 | return false; |
| 111 | } |
| 112 | |
| 113 | /** |
| 114 | * chgrp_ok - verify permissions to chgrp inode |
| 115 | * @idmap: idmap of the mount @inode was found from |
| 116 | * @inode: inode to check permissions on |
| 117 | * @ia_vfsgid: gid to chown @inode to |
| 118 | * |
| 119 | * If the inode has been found through an idmapped mount the idmap of |
| 120 | * the vfsmount must be passed through @idmap. This function will then |
| 121 | * take care to map the inode according to @idmap before checking |
| 122 | * permissions. On non-idmapped mounts or if permission checking is to be |
| 123 | * performed on the raw inode simply pass @nop_mnt_idmap. |
| 124 | */ |
| 125 | static bool chgrp_ok(struct mnt_idmap *idmap, |
| 126 | const struct inode *inode, vfsgid_t ia_vfsgid) |
| 127 | { |
| 128 | vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode); |
| 129 | vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode); |
| 130 | if (vfsuid_eq_kuid(vfsuid, current_fsuid())) { |
| 131 | if (vfsgid_eq(ia_vfsgid, vfsgid)) |
| 132 | return true; |
| 133 | if (vfsgid_in_group_p(ia_vfsgid)) |
| 134 | return true; |
| 135 | } |
| 136 | if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN)) |
| 137 | return true; |
| 138 | if (!vfsgid_valid(vfsgid) && |
| 139 | ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN)) |
| 140 | return true; |
| 141 | return false; |
| 142 | } |
| 143 | |
| 144 | /** |
| 145 | * setattr_prepare - check if attribute changes to a dentry are allowed |
| 146 | * @idmap: idmap of the mount the inode was found from |
| 147 | * @dentry: dentry to check |
| 148 | * @attr: attributes to change |
| 149 | * |
| 150 | * Check if we are allowed to change the attributes contained in @attr |
| 151 | * in the given dentry. This includes the normal unix access permission |
| 152 | * checks, as well as checks for rlimits and others. The function also clears |
| 153 | * SGID bit from mode if user is not allowed to set it. Also file capabilities |
| 154 | * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set. |
| 155 | * |
| 156 | * If the inode has been found through an idmapped mount the idmap of |
| 157 | * the vfsmount must be passed through @idmap. This function will then |
| 158 | * take care to map the inode according to @idmap before checking |
| 159 | * permissions. On non-idmapped mounts or if permission checking is to be |
| 160 | * performed on the raw inode simply passs @nop_mnt_idmap. |
| 161 | * |
| 162 | * Should be called as the first thing in ->setattr implementations, |
| 163 | * possibly after taking additional locks. |
| 164 | */ |
| 165 | int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry, |
| 166 | struct iattr *attr) |
| 167 | { |
| 168 | struct inode *inode = d_inode(dentry); |
| 169 | unsigned int ia_valid = attr->ia_valid; |
| 170 | |
| 171 | /* |
| 172 | * First check size constraints. These can't be overriden using |
| 173 | * ATTR_FORCE. |
| 174 | */ |
| 175 | if (ia_valid & ATTR_SIZE) { |
| 176 | int error = inode_newsize_ok(inode, attr->ia_size); |
| 177 | if (error) |
| 178 | return error; |
| 179 | } |
| 180 | |
| 181 | /* If force is set do it anyway. */ |
| 182 | if (ia_valid & ATTR_FORCE) |
| 183 | goto kill_priv; |
| 184 | |
| 185 | /* Make sure a caller can chown. */ |
| 186 | if ((ia_valid & ATTR_UID) && |
| 187 | !chown_ok(idmap, inode, attr->ia_vfsuid)) |
| 188 | return -EPERM; |
| 189 | |
| 190 | /* Make sure caller can chgrp. */ |
| 191 | if ((ia_valid & ATTR_GID) && |
| 192 | !chgrp_ok(idmap, inode, attr->ia_vfsgid)) |
| 193 | return -EPERM; |
| 194 | |
| 195 | /* Make sure a caller can chmod. */ |
| 196 | if (ia_valid & ATTR_MODE) { |
| 197 | vfsgid_t vfsgid; |
| 198 | |
| 199 | if (!inode_owner_or_capable(idmap, inode)) |
| 200 | return -EPERM; |
| 201 | |
| 202 | if (ia_valid & ATTR_GID) |
| 203 | vfsgid = attr->ia_vfsgid; |
| 204 | else |
| 205 | vfsgid = i_gid_into_vfsgid(idmap, inode); |
| 206 | |
| 207 | /* Also check the setgid bit! */ |
| 208 | if (!in_group_or_capable(idmap, inode, vfsgid)) |
| 209 | attr->ia_mode &= ~S_ISGID; |
| 210 | } |
| 211 | |
| 212 | /* Check for setting the inode time. */ |
| 213 | if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) { |
| 214 | if (!inode_owner_or_capable(idmap, inode)) |
| 215 | return -EPERM; |
| 216 | } |
| 217 | |
| 218 | kill_priv: |
| 219 | /* User has permission for the change */ |
| 220 | if (ia_valid & ATTR_KILL_PRIV) { |
| 221 | int error; |
| 222 | |
| 223 | error = security_inode_killpriv(idmap, dentry); |
| 224 | if (error) |
| 225 | return error; |
| 226 | } |
| 227 | |
| 228 | return 0; |
| 229 | } |
| 230 | EXPORT_SYMBOL(setattr_prepare); |
| 231 | |
| 232 | /** |
| 233 | * inode_newsize_ok - may this inode be truncated to a given size |
| 234 | * @inode: the inode to be truncated |
| 235 | * @offset: the new size to assign to the inode |
| 236 | * |
| 237 | * inode_newsize_ok must be called with i_mutex held. |
| 238 | * |
| 239 | * inode_newsize_ok will check filesystem limits and ulimits to check that the |
| 240 | * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ |
| 241 | * when necessary. Caller must not proceed with inode size change if failure is |
| 242 | * returned. @inode must be a file (not directory), with appropriate |
| 243 | * permissions to allow truncate (inode_newsize_ok does NOT check these |
| 244 | * conditions). |
| 245 | * |
| 246 | * Return: 0 on success, -ve errno on failure |
| 247 | */ |
| 248 | int inode_newsize_ok(const struct inode *inode, loff_t offset) |
| 249 | { |
| 250 | if (offset < 0) |
| 251 | return -EINVAL; |
| 252 | if (inode->i_size < offset) { |
| 253 | unsigned long limit; |
| 254 | |
| 255 | limit = rlimit(RLIMIT_FSIZE); |
| 256 | if (limit != RLIM_INFINITY && offset > limit) |
| 257 | goto out_sig; |
| 258 | if (offset > inode->i_sb->s_maxbytes) |
| 259 | goto out_big; |
| 260 | } else { |
| 261 | /* |
| 262 | * truncation of in-use swapfiles is disallowed - it would |
| 263 | * cause subsequent swapout to scribble on the now-freed |
| 264 | * blocks. |
| 265 | */ |
| 266 | if (IS_SWAPFILE(inode)) |
| 267 | return -ETXTBSY; |
| 268 | } |
| 269 | |
| 270 | return 0; |
| 271 | out_sig: |
| 272 | send_sig(SIGXFSZ, current, 0); |
| 273 | out_big: |
| 274 | return -EFBIG; |
| 275 | } |
| 276 | EXPORT_SYMBOL(inode_newsize_ok); |
| 277 | |
| 278 | /** |
| 279 | * setattr_copy - copy simple metadata updates into the generic inode |
| 280 | * @idmap: idmap of the mount the inode was found from |
| 281 | * @inode: the inode to be updated |
| 282 | * @attr: the new attributes |
| 283 | * |
| 284 | * setattr_copy must be called with i_mutex held. |
| 285 | * |
| 286 | * setattr_copy updates the inode's metadata with that specified |
| 287 | * in attr on idmapped mounts. Necessary permission checks to determine |
| 288 | * whether or not the S_ISGID property needs to be removed are performed with |
| 289 | * the correct idmapped mount permission helpers. |
| 290 | * Noticeably missing is inode size update, which is more complex |
| 291 | * as it requires pagecache updates. |
| 292 | * |
| 293 | * If the inode has been found through an idmapped mount the idmap of |
| 294 | * the vfsmount must be passed through @idmap. This function will then |
| 295 | * take care to map the inode according to @idmap before checking |
| 296 | * permissions. On non-idmapped mounts or if permission checking is to be |
| 297 | * performed on the raw inode simply pass @nop_mnt_idmap. |
| 298 | * |
| 299 | * The inode is not marked as dirty after this operation. The rationale is |
| 300 | * that for "simple" filesystems, the struct inode is the inode storage. |
| 301 | * The caller is free to mark the inode dirty afterwards if needed. |
| 302 | */ |
| 303 | void setattr_copy(struct mnt_idmap *idmap, struct inode *inode, |
| 304 | const struct iattr *attr) |
| 305 | { |
| 306 | unsigned int ia_valid = attr->ia_valid; |
| 307 | |
| 308 | i_uid_update(idmap, attr, inode); |
| 309 | i_gid_update(idmap, attr, inode); |
| 310 | if (ia_valid & ATTR_ATIME) |
| 311 | inode->i_atime = attr->ia_atime; |
| 312 | if (ia_valid & ATTR_MTIME) |
| 313 | inode->i_mtime = attr->ia_mtime; |
| 314 | if (ia_valid & ATTR_CTIME) |
| 315 | inode->i_ctime = attr->ia_ctime; |
| 316 | if (ia_valid & ATTR_MODE) { |
| 317 | umode_t mode = attr->ia_mode; |
| 318 | if (!in_group_or_capable(idmap, inode, |
| 319 | i_gid_into_vfsgid(idmap, inode))) |
| 320 | mode &= ~S_ISGID; |
| 321 | inode->i_mode = mode; |
| 322 | } |
| 323 | } |
| 324 | EXPORT_SYMBOL(setattr_copy); |
| 325 | |
| 326 | int may_setattr(struct mnt_idmap *idmap, struct inode *inode, |
| 327 | unsigned int ia_valid) |
| 328 | { |
| 329 | int error; |
| 330 | |
| 331 | if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) { |
| 332 | if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) |
| 333 | return -EPERM; |
| 334 | } |
| 335 | |
| 336 | /* |
| 337 | * If utimes(2) and friends are called with times == NULL (or both |
| 338 | * times are UTIME_NOW), then we need to check for write permission |
| 339 | */ |
| 340 | if (ia_valid & ATTR_TOUCH) { |
| 341 | if (IS_IMMUTABLE(inode)) |
| 342 | return -EPERM; |
| 343 | |
| 344 | if (!inode_owner_or_capable(idmap, inode)) { |
| 345 | error = inode_permission(idmap, inode, MAY_WRITE); |
| 346 | if (error) |
| 347 | return error; |
| 348 | } |
| 349 | } |
| 350 | return 0; |
| 351 | } |
| 352 | EXPORT_SYMBOL(may_setattr); |
| 353 | |
| 354 | /** |
| 355 | * notify_change - modify attributes of a filesytem object |
| 356 | * @idmap: idmap of the mount the inode was found from |
| 357 | * @dentry: object affected |
| 358 | * @attr: new attributes |
| 359 | * @delegated_inode: returns inode, if the inode is delegated |
| 360 | * |
| 361 | * The caller must hold the i_mutex on the affected object. |
| 362 | * |
| 363 | * If notify_change discovers a delegation in need of breaking, |
| 364 | * it will return -EWOULDBLOCK and return a reference to the inode in |
| 365 | * delegated_inode. The caller should then break the delegation and |
| 366 | * retry. Because breaking a delegation may take a long time, the |
| 367 | * caller should drop the i_mutex before doing so. |
| 368 | * |
| 369 | * Alternatively, a caller may pass NULL for delegated_inode. This may |
| 370 | * be appropriate for callers that expect the underlying filesystem not |
| 371 | * to be NFS exported. Also, passing NULL is fine for callers holding |
| 372 | * the file open for write, as there can be no conflicting delegation in |
| 373 | * that case. |
| 374 | * |
| 375 | * If the inode has been found through an idmapped mount the idmap of |
| 376 | * the vfsmount must be passed through @idmap. This function will then |
| 377 | * take care to map the inode according to @idmap before checking |
| 378 | * permissions. On non-idmapped mounts or if permission checking is to be |
| 379 | * performed on the raw inode simply pass @nop_mnt_idmap. |
| 380 | */ |
| 381 | int notify_change(struct mnt_idmap *idmap, struct dentry *dentry, |
| 382 | struct iattr *attr, struct inode **delegated_inode) |
| 383 | { |
| 384 | struct inode *inode = dentry->d_inode; |
| 385 | umode_t mode = inode->i_mode; |
| 386 | int error; |
| 387 | struct timespec64 now; |
| 388 | unsigned int ia_valid = attr->ia_valid; |
| 389 | |
| 390 | WARN_ON_ONCE(!inode_is_locked(inode)); |
| 391 | |
| 392 | error = may_setattr(idmap, inode, ia_valid); |
| 393 | if (error) |
| 394 | return error; |
| 395 | |
| 396 | if ((ia_valid & ATTR_MODE)) { |
| 397 | umode_t amode = attr->ia_mode; |
| 398 | /* Flag setting protected by i_mutex */ |
| 399 | if (is_sxid(amode)) |
| 400 | inode->i_flags &= ~S_NOSEC; |
| 401 | } |
| 402 | |
| 403 | now = current_time(inode); |
| 404 | |
| 405 | attr->ia_ctime = now; |
| 406 | if (!(ia_valid & ATTR_ATIME_SET)) |
| 407 | attr->ia_atime = now; |
| 408 | else |
| 409 | attr->ia_atime = timestamp_truncate(attr->ia_atime, inode); |
| 410 | if (!(ia_valid & ATTR_MTIME_SET)) |
| 411 | attr->ia_mtime = now; |
| 412 | else |
| 413 | attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode); |
| 414 | |
| 415 | if (ia_valid & ATTR_KILL_PRIV) { |
| 416 | error = security_inode_need_killpriv(dentry); |
| 417 | if (error < 0) |
| 418 | return error; |
| 419 | if (error == 0) |
| 420 | ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; |
| 421 | } |
| 422 | |
| 423 | /* |
| 424 | * We now pass ATTR_KILL_S*ID to the lower level setattr function so |
| 425 | * that the function has the ability to reinterpret a mode change |
| 426 | * that's due to these bits. This adds an implicit restriction that |
| 427 | * no function will ever call notify_change with both ATTR_MODE and |
| 428 | * ATTR_KILL_S*ID set. |
| 429 | */ |
| 430 | if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) && |
| 431 | (ia_valid & ATTR_MODE)) |
| 432 | BUG(); |
| 433 | |
| 434 | if (ia_valid & ATTR_KILL_SUID) { |
| 435 | if (mode & S_ISUID) { |
| 436 | ia_valid = attr->ia_valid |= ATTR_MODE; |
| 437 | attr->ia_mode = (inode->i_mode & ~S_ISUID); |
| 438 | } |
| 439 | } |
| 440 | if (ia_valid & ATTR_KILL_SGID) { |
| 441 | if (mode & S_ISGID) { |
| 442 | if (!(ia_valid & ATTR_MODE)) { |
| 443 | ia_valid = attr->ia_valid |= ATTR_MODE; |
| 444 | attr->ia_mode = inode->i_mode; |
| 445 | } |
| 446 | attr->ia_mode &= ~S_ISGID; |
| 447 | } |
| 448 | } |
| 449 | if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID))) |
| 450 | return 0; |
| 451 | |
| 452 | /* |
| 453 | * Verify that uid/gid changes are valid in the target |
| 454 | * namespace of the superblock. |
| 455 | */ |
| 456 | if (ia_valid & ATTR_UID && |
| 457 | !vfsuid_has_fsmapping(idmap, inode->i_sb->s_user_ns, |
| 458 | attr->ia_vfsuid)) |
| 459 | return -EOVERFLOW; |
| 460 | if (ia_valid & ATTR_GID && |
| 461 | !vfsgid_has_fsmapping(idmap, inode->i_sb->s_user_ns, |
| 462 | attr->ia_vfsgid)) |
| 463 | return -EOVERFLOW; |
| 464 | |
| 465 | /* Don't allow modifications of files with invalid uids or |
| 466 | * gids unless those uids & gids are being made valid. |
| 467 | */ |
| 468 | if (!(ia_valid & ATTR_UID) && |
| 469 | !vfsuid_valid(i_uid_into_vfsuid(idmap, inode))) |
| 470 | return -EOVERFLOW; |
| 471 | if (!(ia_valid & ATTR_GID) && |
| 472 | !vfsgid_valid(i_gid_into_vfsgid(idmap, inode))) |
| 473 | return -EOVERFLOW; |
| 474 | |
| 475 | error = security_inode_setattr(idmap, dentry, attr); |
| 476 | if (error) |
| 477 | return error; |
| 478 | error = try_break_deleg(inode, delegated_inode); |
| 479 | if (error) |
| 480 | return error; |
| 481 | |
| 482 | if (inode->i_op->setattr) |
| 483 | error = inode->i_op->setattr(idmap, dentry, attr); |
| 484 | else |
| 485 | error = simple_setattr(idmap, dentry, attr); |
| 486 | |
| 487 | if (!error) { |
| 488 | fsnotify_change(dentry, ia_valid); |
| 489 | ima_inode_post_setattr(idmap, dentry); |
| 490 | evm_inode_post_setattr(dentry, ia_valid); |
| 491 | } |
| 492 | |
| 493 | return error; |
| 494 | } |
| 495 | EXPORT_SYMBOL(notify_change); |