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