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 chown_ok(const struct inode * inode,kuid_t uid)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 chgrp_ok(const struct inode * inode,kgid_t gid)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 */ setattr_prepare(struct dentry * dentry,struct iattr * attr)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 */ inode_newsize_ok(const struct inode * inode,loff_t offset)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 */ setattr_copy(struct inode * inode,const struct iattr * attr)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 = attr->ia_atime; 188 if (ia_valid & ATTR_MTIME) 189 inode->i_mtime = attr->ia_mtime; 190 if (ia_valid & ATTR_CTIME) 191 inode->i_ctime = attr->ia_ctime; 192 if (ia_valid & ATTR_MODE) { 193 umode_t mode = attr->ia_mode; 194 195 if (!in_group_p(inode->i_gid) && 196 !capable_wrt_inode_uidgid(inode, CAP_FSETID)) 197 mode &= ~S_ISGID; 198 inode->i_mode = mode; 199 } 200 } 201 EXPORT_SYMBOL(setattr_copy); 202 203 /** 204 * notify_change - modify attributes of a filesytem object 205 * @dentry: object affected 206 * @attr: new attributes 207 * @delegated_inode: returns inode, if the inode is delegated 208 * 209 * The caller must hold the i_mutex on the affected object. 210 * 211 * If notify_change discovers a delegation in need of breaking, 212 * it will return -EWOULDBLOCK and return a reference to the inode in 213 * delegated_inode. The caller should then break the delegation and 214 * retry. Because breaking a delegation may take a long time, the 215 * caller should drop the i_mutex before doing so. 216 * 217 * Alternatively, a caller may pass NULL for delegated_inode. This may 218 * be appropriate for callers that expect the underlying filesystem not 219 * to be NFS exported. Also, passing NULL is fine for callers holding 220 * the file open for write, as there can be no conflicting delegation in 221 * that case. 222 */ notify_change(struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)223 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode) 224 { 225 struct inode *inode = dentry->d_inode; 226 umode_t mode = inode->i_mode; 227 int error; 228 struct timespec64 now; 229 unsigned int ia_valid = attr->ia_valid; 230 231 WARN_ON_ONCE(!inode_is_locked(inode)); 232 233 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) { 234 if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) 235 return -EPERM; 236 } 237 238 /* 239 * If utimes(2) and friends are called with times == NULL (or both 240 * times are UTIME_NOW), then we need to check for write permission 241 */ 242 if (ia_valid & ATTR_TOUCH) { 243 if (IS_IMMUTABLE(inode)) 244 return -EPERM; 245 246 if (!inode_owner_or_capable(inode)) { 247 error = inode_permission(inode, MAY_WRITE); 248 if (error) 249 return error; 250 } 251 } 252 253 if ((ia_valid & ATTR_MODE)) { 254 umode_t amode = attr->ia_mode; 255 /* Flag setting protected by i_mutex */ 256 if (is_sxid(amode)) 257 inode->i_flags &= ~S_NOSEC; 258 } 259 260 now = current_time(inode); 261 262 attr->ia_ctime = now; 263 if (!(ia_valid & ATTR_ATIME_SET)) 264 attr->ia_atime = now; 265 else 266 attr->ia_atime = timestamp_truncate(attr->ia_atime, inode); 267 if (!(ia_valid & ATTR_MTIME_SET)) 268 attr->ia_mtime = now; 269 else 270 attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode); 271 272 if (ia_valid & ATTR_KILL_PRIV) { 273 error = security_inode_need_killpriv(dentry); 274 if (error < 0) 275 return error; 276 if (error == 0) 277 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; 278 } 279 280 /* 281 * We now pass ATTR_KILL_S*ID to the lower level setattr function so 282 * that the function has the ability to reinterpret a mode change 283 * that's due to these bits. This adds an implicit restriction that 284 * no function will ever call notify_change with both ATTR_MODE and 285 * ATTR_KILL_S*ID set. 286 */ 287 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) && 288 (ia_valid & ATTR_MODE)) 289 BUG(); 290 291 if (ia_valid & ATTR_KILL_SUID) { 292 if (mode & S_ISUID) { 293 ia_valid = attr->ia_valid |= ATTR_MODE; 294 attr->ia_mode = (inode->i_mode & ~S_ISUID); 295 } 296 } 297 if (ia_valid & ATTR_KILL_SGID) { 298 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { 299 if (!(ia_valid & ATTR_MODE)) { 300 ia_valid = attr->ia_valid |= ATTR_MODE; 301 attr->ia_mode = inode->i_mode; 302 } 303 attr->ia_mode &= ~S_ISGID; 304 } 305 } 306 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID))) 307 return 0; 308 309 /* 310 * Verify that uid/gid changes are valid in the target 311 * namespace of the superblock. 312 */ 313 if (ia_valid & ATTR_UID && 314 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid)) 315 return -EOVERFLOW; 316 if (ia_valid & ATTR_GID && 317 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid)) 318 return -EOVERFLOW; 319 320 /* Don't allow modifications of files with invalid uids or 321 * gids unless those uids & gids are being made valid. 322 */ 323 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid)) 324 return -EOVERFLOW; 325 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid)) 326 return -EOVERFLOW; 327 328 error = security_inode_setattr(dentry, attr); 329 if (error) 330 return error; 331 error = try_break_deleg(inode, delegated_inode); 332 if (error) 333 return error; 334 335 if (inode->i_op->setattr) 336 error = inode->i_op->setattr(dentry, attr); 337 else 338 error = simple_setattr(dentry, attr); 339 340 if (!error) { 341 fsnotify_change(dentry, ia_valid); 342 ima_inode_post_setattr(dentry); 343 evm_inode_post_setattr(dentry, ia_valid); 344 } 345 346 return error; 347 } 348 EXPORT_SYMBOL(notify_change); 349