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 * @Returns: 0 on success, -ve errno on failure 124 * 125 * inode_newsize_ok must be called with i_mutex held. 126 * 127 * inode_newsize_ok will check filesystem limits and ulimits to check that the 128 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ 129 * when necessary. Caller must not proceed with inode size change if failure is 130 * returned. @inode must be a file (not directory), with appropriate 131 * permissions to allow truncate (inode_newsize_ok does NOT check these 132 * conditions). 133 */ 134 int inode_newsize_ok(const struct inode *inode, loff_t offset) 135 { 136 if (inode->i_size < offset) { 137 unsigned long limit; 138 139 limit = rlimit(RLIMIT_FSIZE); 140 if (limit != RLIM_INFINITY && offset > limit) 141 goto out_sig; 142 if (offset > inode->i_sb->s_maxbytes) 143 goto out_big; 144 } else { 145 /* 146 * truncation of in-use swapfiles is disallowed - it would 147 * cause subsequent swapout to scribble on the now-freed 148 * blocks. 149 */ 150 if (IS_SWAPFILE(inode)) 151 return -ETXTBSY; 152 } 153 154 return 0; 155 out_sig: 156 send_sig(SIGXFSZ, current, 0); 157 out_big: 158 return -EFBIG; 159 } 160 EXPORT_SYMBOL(inode_newsize_ok); 161 162 /** 163 * setattr_copy - copy simple metadata updates into the generic inode 164 * @inode: the inode to be updated 165 * @attr: the new attributes 166 * 167 * setattr_copy must be called with i_mutex held. 168 * 169 * setattr_copy updates the inode's metadata with that specified 170 * in attr. Noticeably missing is inode size update, which is more complex 171 * as it requires pagecache updates. 172 * 173 * The inode is not marked as dirty after this operation. The rationale is 174 * that for "simple" filesystems, the struct inode is the inode storage. 175 * The caller is free to mark the inode dirty afterwards if needed. 176 */ 177 void setattr_copy(struct inode *inode, const struct iattr *attr) 178 { 179 unsigned int ia_valid = attr->ia_valid; 180 181 if (ia_valid & ATTR_UID) 182 inode->i_uid = attr->ia_uid; 183 if (ia_valid & ATTR_GID) 184 inode->i_gid = attr->ia_gid; 185 if (ia_valid & ATTR_ATIME) 186 inode->i_atime = timespec64_trunc(attr->ia_atime, 187 inode->i_sb->s_time_gran); 188 if (ia_valid & ATTR_MTIME) 189 inode->i_mtime = timespec64_trunc(attr->ia_mtime, 190 inode->i_sb->s_time_gran); 191 if (ia_valid & ATTR_CTIME) 192 inode->i_ctime = timespec64_trunc(attr->ia_ctime, 193 inode->i_sb->s_time_gran); 194 if (ia_valid & ATTR_MODE) { 195 umode_t mode = attr->ia_mode; 196 197 if (!in_group_p(inode->i_gid) && 198 !capable_wrt_inode_uidgid(inode, CAP_FSETID)) 199 mode &= ~S_ISGID; 200 inode->i_mode = mode; 201 } 202 } 203 EXPORT_SYMBOL(setattr_copy); 204 205 /** 206 * notify_change - modify attributes of a filesytem object 207 * @dentry: object affected 208 * @iattr: new attributes 209 * @delegated_inode: returns inode, if the inode is delegated 210 * 211 * The caller must hold the i_mutex on the affected object. 212 * 213 * If notify_change discovers a delegation in need of breaking, 214 * it will return -EWOULDBLOCK and return a reference to the inode in 215 * delegated_inode. The caller should then break the delegation and 216 * retry. Because breaking a delegation may take a long time, the 217 * caller should drop the i_mutex before doing so. 218 * 219 * Alternatively, a caller may pass NULL for delegated_inode. This may 220 * be appropriate for callers that expect the underlying filesystem not 221 * to be NFS exported. Also, passing NULL is fine for callers holding 222 * the file open for write, as there can be no conflicting delegation in 223 * that case. 224 */ 225 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode) 226 { 227 struct inode *inode = dentry->d_inode; 228 umode_t mode = inode->i_mode; 229 int error; 230 struct timespec64 now; 231 unsigned int ia_valid = attr->ia_valid; 232 233 WARN_ON_ONCE(!inode_is_locked(inode)); 234 235 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) { 236 if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) 237 return -EPERM; 238 } 239 240 /* 241 * If utimes(2) and friends are called with times == NULL (or both 242 * times are UTIME_NOW), then we need to check for write permission 243 */ 244 if (ia_valid & ATTR_TOUCH) { 245 if (IS_IMMUTABLE(inode)) 246 return -EPERM; 247 248 if (!inode_owner_or_capable(inode)) { 249 error = inode_permission(inode, MAY_WRITE); 250 if (error) 251 return error; 252 } 253 } 254 255 if ((ia_valid & ATTR_MODE)) { 256 umode_t amode = attr->ia_mode; 257 /* Flag setting protected by i_mutex */ 258 if (is_sxid(amode)) 259 inode->i_flags &= ~S_NOSEC; 260 } 261 262 now = current_time(inode); 263 264 attr->ia_ctime = now; 265 if (!(ia_valid & ATTR_ATIME_SET)) 266 attr->ia_atime = now; 267 if (!(ia_valid & ATTR_MTIME_SET)) 268 attr->ia_mtime = now; 269 if (ia_valid & ATTR_KILL_PRIV) { 270 error = security_inode_need_killpriv(dentry); 271 if (error < 0) 272 return error; 273 if (error == 0) 274 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; 275 } 276 277 /* 278 * We now pass ATTR_KILL_S*ID to the lower level setattr function so 279 * that the function has the ability to reinterpret a mode change 280 * that's due to these bits. This adds an implicit restriction that 281 * no function will ever call notify_change with both ATTR_MODE and 282 * ATTR_KILL_S*ID set. 283 */ 284 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) && 285 (ia_valid & ATTR_MODE)) 286 BUG(); 287 288 if (ia_valid & ATTR_KILL_SUID) { 289 if (mode & S_ISUID) { 290 ia_valid = attr->ia_valid |= ATTR_MODE; 291 attr->ia_mode = (inode->i_mode & ~S_ISUID); 292 } 293 } 294 if (ia_valid & ATTR_KILL_SGID) { 295 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { 296 if (!(ia_valid & ATTR_MODE)) { 297 ia_valid = attr->ia_valid |= ATTR_MODE; 298 attr->ia_mode = inode->i_mode; 299 } 300 attr->ia_mode &= ~S_ISGID; 301 } 302 } 303 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID))) 304 return 0; 305 306 /* 307 * Verify that uid/gid changes are valid in the target 308 * namespace of the superblock. 309 */ 310 if (ia_valid & ATTR_UID && 311 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid)) 312 return -EOVERFLOW; 313 if (ia_valid & ATTR_GID && 314 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid)) 315 return -EOVERFLOW; 316 317 /* Don't allow modifications of files with invalid uids or 318 * gids unless those uids & gids are being made valid. 319 */ 320 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid)) 321 return -EOVERFLOW; 322 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid)) 323 return -EOVERFLOW; 324 325 error = security_inode_setattr(dentry, attr); 326 if (error) 327 return error; 328 error = try_break_deleg(inode, delegated_inode); 329 if (error) 330 return error; 331 332 if (inode->i_op->setattr) 333 error = inode->i_op->setattr(dentry, attr); 334 else 335 error = simple_setattr(dentry, attr); 336 337 if (!error) { 338 fsnotify_change(dentry, ia_valid); 339 ima_inode_post_setattr(dentry); 340 evm_inode_post_setattr(dentry, ia_valid); 341 } 342 343 return error; 344 } 345 EXPORT_SYMBOL(notify_change); 346