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/security.h> 18 #include <linux/evm.h> 19 #include <linux/ima.h> 20 21 /** 22 * chown_ok - verify permissions to chown inode 23 * @mnt_userns: user namespace of the mount @inode was found from 24 * @inode: inode to check permissions on 25 * @uid: uid to chown @inode to 26 * 27 * If the inode has been found through an idmapped mount the user namespace of 28 * the vfsmount must be passed through @mnt_userns. This function will then 29 * take care to map the inode according to @mnt_userns before checking 30 * permissions. On non-idmapped mounts or if permission checking is to be 31 * performed on the raw inode simply passs init_user_ns. 32 */ 33 static bool chown_ok(struct user_namespace *mnt_userns, 34 const struct inode *inode, 35 kuid_t uid) 36 { 37 kuid_t kuid = i_uid_into_mnt(mnt_userns, inode); 38 if (uid_eq(current_fsuid(), kuid) && uid_eq(uid, kuid)) 39 return true; 40 if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN)) 41 return true; 42 if (uid_eq(kuid, INVALID_UID) && 43 ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN)) 44 return true; 45 return false; 46 } 47 48 /** 49 * chgrp_ok - verify permissions to chgrp inode 50 * @mnt_userns: user namespace of the mount @inode was found from 51 * @inode: inode to check permissions on 52 * @gid: gid to chown @inode to 53 * 54 * If the inode has been found through an idmapped mount the user namespace of 55 * the vfsmount must be passed through @mnt_userns. This function will then 56 * take care to map the inode according to @mnt_userns before checking 57 * permissions. On non-idmapped mounts or if permission checking is to be 58 * performed on the raw inode simply passs init_user_ns. 59 */ 60 static bool chgrp_ok(struct user_namespace *mnt_userns, 61 const struct inode *inode, kgid_t gid) 62 { 63 kgid_t kgid = i_gid_into_mnt(mnt_userns, inode); 64 if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) && 65 (in_group_p(gid) || gid_eq(gid, kgid))) 66 return true; 67 if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN)) 68 return true; 69 if (gid_eq(kgid, INVALID_GID) && 70 ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN)) 71 return true; 72 return false; 73 } 74 75 /** 76 * setattr_prepare - check if attribute changes to a dentry are allowed 77 * @mnt_userns: user namespace of the mount the inode was found from 78 * @dentry: dentry to check 79 * @attr: attributes to change 80 * 81 * Check if we are allowed to change the attributes contained in @attr 82 * in the given dentry. This includes the normal unix access permission 83 * checks, as well as checks for rlimits and others. The function also clears 84 * SGID bit from mode if user is not allowed to set it. Also file capabilities 85 * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set. 86 * 87 * If the inode has been found through an idmapped mount the user namespace of 88 * the vfsmount must be passed through @mnt_userns. This function will then 89 * take care to map the inode according to @mnt_userns before checking 90 * permissions. On non-idmapped mounts or if permission checking is to be 91 * performed on the raw inode simply passs init_user_ns. 92 * 93 * Should be called as the first thing in ->setattr implementations, 94 * possibly after taking additional locks. 95 */ 96 int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry, 97 struct iattr *attr) 98 { 99 struct inode *inode = d_inode(dentry); 100 unsigned int ia_valid = attr->ia_valid; 101 102 /* 103 * First check size constraints. These can't be overriden using 104 * ATTR_FORCE. 105 */ 106 if (ia_valid & ATTR_SIZE) { 107 int error = inode_newsize_ok(inode, attr->ia_size); 108 if (error) 109 return error; 110 } 111 112 /* If force is set do it anyway. */ 113 if (ia_valid & ATTR_FORCE) 114 goto kill_priv; 115 116 /* Make sure a caller can chown. */ 117 if ((ia_valid & ATTR_UID) && !chown_ok(mnt_userns, inode, attr->ia_uid)) 118 return -EPERM; 119 120 /* Make sure caller can chgrp. */ 121 if ((ia_valid & ATTR_GID) && !chgrp_ok(mnt_userns, inode, attr->ia_gid)) 122 return -EPERM; 123 124 /* Make sure a caller can chmod. */ 125 if (ia_valid & ATTR_MODE) { 126 if (!inode_owner_or_capable(mnt_userns, inode)) 127 return -EPERM; 128 /* Also check the setgid bit! */ 129 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid : 130 i_gid_into_mnt(mnt_userns, inode)) && 131 !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) 132 attr->ia_mode &= ~S_ISGID; 133 } 134 135 /* Check for setting the inode time. */ 136 if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) { 137 if (!inode_owner_or_capable(mnt_userns, inode)) 138 return -EPERM; 139 } 140 141 kill_priv: 142 /* User has permission for the change */ 143 if (ia_valid & ATTR_KILL_PRIV) { 144 int error; 145 146 error = security_inode_killpriv(mnt_userns, dentry); 147 if (error) 148 return error; 149 } 150 151 return 0; 152 } 153 EXPORT_SYMBOL(setattr_prepare); 154 155 /** 156 * inode_newsize_ok - may this inode be truncated to a given size 157 * @inode: the inode to be truncated 158 * @offset: the new size to assign to the inode 159 * 160 * inode_newsize_ok must be called with i_mutex held. 161 * 162 * inode_newsize_ok will check filesystem limits and ulimits to check that the 163 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ 164 * when necessary. Caller must not proceed with inode size change if failure is 165 * returned. @inode must be a file (not directory), with appropriate 166 * permissions to allow truncate (inode_newsize_ok does NOT check these 167 * conditions). 168 * 169 * Return: 0 on success, -ve errno on failure 170 */ 171 int inode_newsize_ok(const struct inode *inode, loff_t offset) 172 { 173 if (inode->i_size < offset) { 174 unsigned long limit; 175 176 limit = rlimit(RLIMIT_FSIZE); 177 if (limit != RLIM_INFINITY && offset > limit) 178 goto out_sig; 179 if (offset > inode->i_sb->s_maxbytes) 180 goto out_big; 181 } else { 182 /* 183 * truncation of in-use swapfiles is disallowed - it would 184 * cause subsequent swapout to scribble on the now-freed 185 * blocks. 186 */ 187 if (IS_SWAPFILE(inode)) 188 return -ETXTBSY; 189 } 190 191 return 0; 192 out_sig: 193 send_sig(SIGXFSZ, current, 0); 194 out_big: 195 return -EFBIG; 196 } 197 EXPORT_SYMBOL(inode_newsize_ok); 198 199 /** 200 * setattr_copy - copy simple metadata updates into the generic inode 201 * @mnt_userns: user namespace of the mount the inode was found from 202 * @inode: the inode to be updated 203 * @attr: the new attributes 204 * 205 * setattr_copy must be called with i_mutex held. 206 * 207 * setattr_copy updates the inode's metadata with that specified 208 * in attr on idmapped mounts. If file ownership is changed setattr_copy 209 * doesn't map ia_uid and ia_gid. It will asssume the caller has already 210 * provided the intended values. Necessary permission checks to determine 211 * whether or not the S_ISGID property needs to be removed are performed with 212 * the correct idmapped mount permission helpers. 213 * Noticeably missing is inode size update, which is more complex 214 * as it requires pagecache updates. 215 * 216 * If the inode has been found through an idmapped mount the user namespace of 217 * the vfsmount must be passed through @mnt_userns. This function will then 218 * take care to map the inode according to @mnt_userns before checking 219 * permissions. On non-idmapped mounts or if permission checking is to be 220 * performed on the raw inode simply passs init_user_ns. 221 * 222 * The inode is not marked as dirty after this operation. The rationale is 223 * that for "simple" filesystems, the struct inode is the inode storage. 224 * The caller is free to mark the inode dirty afterwards if needed. 225 */ 226 void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode, 227 const struct iattr *attr) 228 { 229 unsigned int ia_valid = attr->ia_valid; 230 231 if (ia_valid & ATTR_UID) 232 inode->i_uid = attr->ia_uid; 233 if (ia_valid & ATTR_GID) 234 inode->i_gid = attr->ia_gid; 235 if (ia_valid & ATTR_ATIME) 236 inode->i_atime = attr->ia_atime; 237 if (ia_valid & ATTR_MTIME) 238 inode->i_mtime = attr->ia_mtime; 239 if (ia_valid & ATTR_CTIME) 240 inode->i_ctime = attr->ia_ctime; 241 if (ia_valid & ATTR_MODE) { 242 umode_t mode = attr->ia_mode; 243 kgid_t kgid = i_gid_into_mnt(mnt_userns, inode); 244 if (!in_group_p(kgid) && 245 !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) 246 mode &= ~S_ISGID; 247 inode->i_mode = mode; 248 } 249 } 250 EXPORT_SYMBOL(setattr_copy); 251 252 /** 253 * notify_change - modify attributes of a filesytem object 254 * @mnt_userns: user namespace of the mount the inode was found from 255 * @dentry: object affected 256 * @attr: new attributes 257 * @delegated_inode: returns inode, if the inode is delegated 258 * 259 * The caller must hold the i_mutex on the affected object. 260 * 261 * If notify_change discovers a delegation in need of breaking, 262 * it will return -EWOULDBLOCK and return a reference to the inode in 263 * delegated_inode. The caller should then break the delegation and 264 * retry. Because breaking a delegation may take a long time, the 265 * caller should drop the i_mutex before doing so. 266 * 267 * If file ownership is changed notify_change() doesn't map ia_uid and 268 * ia_gid. It will asssume the caller has already provided the intended values. 269 * 270 * Alternatively, a caller may pass NULL for delegated_inode. This may 271 * be appropriate for callers that expect the underlying filesystem not 272 * to be NFS exported. Also, passing NULL is fine for callers holding 273 * the file open for write, as there can be no conflicting delegation in 274 * that case. 275 * 276 * If the inode has been found through an idmapped mount the user namespace of 277 * the vfsmount must be passed through @mnt_userns. This function will then 278 * take care to map the inode according to @mnt_userns before checking 279 * permissions. On non-idmapped mounts or if permission checking is to be 280 * performed on the raw inode simply passs init_user_ns. 281 */ 282 int notify_change(struct user_namespace *mnt_userns, struct dentry *dentry, 283 struct iattr *attr, struct inode **delegated_inode) 284 { 285 struct inode *inode = dentry->d_inode; 286 umode_t mode = inode->i_mode; 287 int error; 288 struct timespec64 now; 289 unsigned int ia_valid = attr->ia_valid; 290 291 WARN_ON_ONCE(!inode_is_locked(inode)); 292 293 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) { 294 if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) 295 return -EPERM; 296 } 297 298 /* 299 * If utimes(2) and friends are called with times == NULL (or both 300 * times are UTIME_NOW), then we need to check for write permission 301 */ 302 if (ia_valid & ATTR_TOUCH) { 303 if (IS_IMMUTABLE(inode)) 304 return -EPERM; 305 306 if (!inode_owner_or_capable(mnt_userns, inode)) { 307 error = inode_permission(mnt_userns, inode, MAY_WRITE); 308 if (error) 309 return error; 310 } 311 } 312 313 if ((ia_valid & ATTR_MODE)) { 314 umode_t amode = attr->ia_mode; 315 /* Flag setting protected by i_mutex */ 316 if (is_sxid(amode)) 317 inode->i_flags &= ~S_NOSEC; 318 } 319 320 now = current_time(inode); 321 322 attr->ia_ctime = now; 323 if (!(ia_valid & ATTR_ATIME_SET)) 324 attr->ia_atime = now; 325 else 326 attr->ia_atime = timestamp_truncate(attr->ia_atime, inode); 327 if (!(ia_valid & ATTR_MTIME_SET)) 328 attr->ia_mtime = now; 329 else 330 attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode); 331 332 if (ia_valid & ATTR_KILL_PRIV) { 333 error = security_inode_need_killpriv(dentry); 334 if (error < 0) 335 return error; 336 if (error == 0) 337 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; 338 } 339 340 /* 341 * We now pass ATTR_KILL_S*ID to the lower level setattr function so 342 * that the function has the ability to reinterpret a mode change 343 * that's due to these bits. This adds an implicit restriction that 344 * no function will ever call notify_change with both ATTR_MODE and 345 * ATTR_KILL_S*ID set. 346 */ 347 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) && 348 (ia_valid & ATTR_MODE)) 349 BUG(); 350 351 if (ia_valid & ATTR_KILL_SUID) { 352 if (mode & S_ISUID) { 353 ia_valid = attr->ia_valid |= ATTR_MODE; 354 attr->ia_mode = (inode->i_mode & ~S_ISUID); 355 } 356 } 357 if (ia_valid & ATTR_KILL_SGID) { 358 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { 359 if (!(ia_valid & ATTR_MODE)) { 360 ia_valid = attr->ia_valid |= ATTR_MODE; 361 attr->ia_mode = inode->i_mode; 362 } 363 attr->ia_mode &= ~S_ISGID; 364 } 365 } 366 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID))) 367 return 0; 368 369 /* 370 * Verify that uid/gid changes are valid in the target 371 * namespace of the superblock. 372 */ 373 if (ia_valid & ATTR_UID && 374 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid)) 375 return -EOVERFLOW; 376 if (ia_valid & ATTR_GID && 377 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid)) 378 return -EOVERFLOW; 379 380 /* Don't allow modifications of files with invalid uids or 381 * gids unless those uids & gids are being made valid. 382 */ 383 if (!(ia_valid & ATTR_UID) && 384 !uid_valid(i_uid_into_mnt(mnt_userns, inode))) 385 return -EOVERFLOW; 386 if (!(ia_valid & ATTR_GID) && 387 !gid_valid(i_gid_into_mnt(mnt_userns, inode))) 388 return -EOVERFLOW; 389 390 error = security_inode_setattr(dentry, attr); 391 if (error) 392 return error; 393 error = try_break_deleg(inode, delegated_inode); 394 if (error) 395 return error; 396 397 if (inode->i_op->setattr) 398 error = inode->i_op->setattr(mnt_userns, dentry, attr); 399 else 400 error = simple_setattr(mnt_userns, dentry, attr); 401 402 if (!error) { 403 fsnotify_change(dentry, ia_valid); 404 ima_inode_post_setattr(mnt_userns, dentry); 405 evm_inode_post_setattr(dentry, ia_valid); 406 } 407 408 return error; 409 } 410 EXPORT_SYMBOL(notify_change); 411