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