1 /* 2 * linux/fs/attr.c 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 * changes by Thomas Schoebel-Theuer 6 */ 7 8 #include <linux/export.h> 9 #include <linux/time.h> 10 #include <linux/mm.h> 11 #include <linux/string.h> 12 #include <linux/sched/signal.h> 13 #include <linux/capability.h> 14 #include <linux/fsnotify.h> 15 #include <linux/fcntl.h> 16 #include <linux/security.h> 17 #include <linux/evm.h> 18 #include <linux/ima.h> 19 20 /** 21 * setattr_prepare - check if attribute changes to a dentry are allowed 22 * @dentry: dentry to check 23 * @attr: attributes to change 24 * 25 * Check if we are allowed to change the attributes contained in @attr 26 * in the given dentry. This includes the normal unix access permission 27 * checks, as well as checks for rlimits and others. The function also clears 28 * SGID bit from mode if user is not allowed to set it. Also file capabilities 29 * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set. 30 * 31 * Should be called as the first thing in ->setattr implementations, 32 * possibly after taking additional locks. 33 */ 34 int setattr_prepare(struct dentry *dentry, struct iattr *attr) 35 { 36 struct inode *inode = d_inode(dentry); 37 unsigned int ia_valid = attr->ia_valid; 38 39 /* 40 * First check size constraints. These can't be overriden using 41 * ATTR_FORCE. 42 */ 43 if (ia_valid & ATTR_SIZE) { 44 int error = inode_newsize_ok(inode, attr->ia_size); 45 if (error) 46 return error; 47 } 48 49 /* If force is set do it anyway. */ 50 if (ia_valid & ATTR_FORCE) 51 goto kill_priv; 52 53 /* Make sure a caller can chown. */ 54 if ((ia_valid & ATTR_UID) && 55 (!uid_eq(current_fsuid(), inode->i_uid) || 56 !uid_eq(attr->ia_uid, inode->i_uid)) && 57 !capable_wrt_inode_uidgid(inode, CAP_CHOWN)) 58 return -EPERM; 59 60 /* Make sure caller can chgrp. */ 61 if ((ia_valid & ATTR_GID) && 62 (!uid_eq(current_fsuid(), inode->i_uid) || 63 (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) && 64 !capable_wrt_inode_uidgid(inode, CAP_CHOWN)) 65 return -EPERM; 66 67 /* Make sure a caller can chmod. */ 68 if (ia_valid & ATTR_MODE) { 69 if (!inode_owner_or_capable(inode)) 70 return -EPERM; 71 /* Also check the setgid bit! */ 72 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid : 73 inode->i_gid) && 74 !capable_wrt_inode_uidgid(inode, CAP_FSETID)) 75 attr->ia_mode &= ~S_ISGID; 76 } 77 78 /* Check for setting the inode time. */ 79 if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) { 80 if (!inode_owner_or_capable(inode)) 81 return -EPERM; 82 } 83 84 kill_priv: 85 /* User has permission for the change */ 86 if (ia_valid & ATTR_KILL_PRIV) { 87 int error; 88 89 error = security_inode_killpriv(dentry); 90 if (error) 91 return error; 92 } 93 94 return 0; 95 } 96 EXPORT_SYMBOL(setattr_prepare); 97 98 /** 99 * inode_newsize_ok - may this inode be truncated to a given size 100 * @inode: the inode to be truncated 101 * @offset: the new size to assign to the inode 102 * @Returns: 0 on success, -ve errno on failure 103 * 104 * inode_newsize_ok must be called with i_mutex held. 105 * 106 * inode_newsize_ok will check filesystem limits and ulimits to check that the 107 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ 108 * when necessary. Caller must not proceed with inode size change if failure is 109 * returned. @inode must be a file (not directory), with appropriate 110 * permissions to allow truncate (inode_newsize_ok does NOT check these 111 * conditions). 112 */ 113 int inode_newsize_ok(const struct inode *inode, loff_t offset) 114 { 115 if (inode->i_size < offset) { 116 unsigned long limit; 117 118 limit = rlimit(RLIMIT_FSIZE); 119 if (limit != RLIM_INFINITY && offset > limit) 120 goto out_sig; 121 if (offset > inode->i_sb->s_maxbytes) 122 goto out_big; 123 } else { 124 /* 125 * truncation of in-use swapfiles is disallowed - it would 126 * cause subsequent swapout to scribble on the now-freed 127 * blocks. 128 */ 129 if (IS_SWAPFILE(inode)) 130 return -ETXTBSY; 131 } 132 133 return 0; 134 out_sig: 135 send_sig(SIGXFSZ, current, 0); 136 out_big: 137 return -EFBIG; 138 } 139 EXPORT_SYMBOL(inode_newsize_ok); 140 141 /** 142 * setattr_copy - copy simple metadata updates into the generic inode 143 * @inode: the inode to be updated 144 * @attr: the new attributes 145 * 146 * setattr_copy must be called with i_mutex held. 147 * 148 * setattr_copy updates the inode's metadata with that specified 149 * in attr. Noticeably missing is inode size update, which is more complex 150 * as it requires pagecache updates. 151 * 152 * The inode is not marked as dirty after this operation. The rationale is 153 * that for "simple" filesystems, the struct inode is the inode storage. 154 * The caller is free to mark the inode dirty afterwards if needed. 155 */ 156 void setattr_copy(struct inode *inode, const struct iattr *attr) 157 { 158 unsigned int ia_valid = attr->ia_valid; 159 160 if (ia_valid & ATTR_UID) 161 inode->i_uid = attr->ia_uid; 162 if (ia_valid & ATTR_GID) 163 inode->i_gid = attr->ia_gid; 164 if (ia_valid & ATTR_ATIME) 165 inode->i_atime = timespec_trunc(attr->ia_atime, 166 inode->i_sb->s_time_gran); 167 if (ia_valid & ATTR_MTIME) 168 inode->i_mtime = timespec_trunc(attr->ia_mtime, 169 inode->i_sb->s_time_gran); 170 if (ia_valid & ATTR_CTIME) 171 inode->i_ctime = timespec_trunc(attr->ia_ctime, 172 inode->i_sb->s_time_gran); 173 if (ia_valid & ATTR_MODE) { 174 umode_t mode = attr->ia_mode; 175 176 if (!in_group_p(inode->i_gid) && 177 !capable_wrt_inode_uidgid(inode, CAP_FSETID)) 178 mode &= ~S_ISGID; 179 inode->i_mode = mode; 180 } 181 } 182 EXPORT_SYMBOL(setattr_copy); 183 184 /** 185 * notify_change - modify attributes of a filesytem object 186 * @dentry: object affected 187 * @iattr: new attributes 188 * @delegated_inode: returns inode, if the inode is delegated 189 * 190 * The caller must hold the i_mutex on the affected object. 191 * 192 * If notify_change discovers a delegation in need of breaking, 193 * it will return -EWOULDBLOCK and return a reference to the inode in 194 * delegated_inode. The caller should then break the delegation and 195 * retry. Because breaking a delegation may take a long time, the 196 * caller should drop the i_mutex before doing so. 197 * 198 * Alternatively, a caller may pass NULL for delegated_inode. This may 199 * be appropriate for callers that expect the underlying filesystem not 200 * to be NFS exported. Also, passing NULL is fine for callers holding 201 * the file open for write, as there can be no conflicting delegation in 202 * that case. 203 */ 204 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode) 205 { 206 struct inode *inode = dentry->d_inode; 207 umode_t mode = inode->i_mode; 208 int error; 209 struct timespec now; 210 unsigned int ia_valid = attr->ia_valid; 211 212 WARN_ON_ONCE(!inode_is_locked(inode)); 213 214 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) { 215 if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) 216 return -EPERM; 217 } 218 219 /* 220 * If utimes(2) and friends are called with times == NULL (or both 221 * times are UTIME_NOW), then we need to check for write permission 222 */ 223 if (ia_valid & ATTR_TOUCH) { 224 if (IS_IMMUTABLE(inode)) 225 return -EPERM; 226 227 if (!inode_owner_or_capable(inode)) { 228 error = inode_permission(inode, MAY_WRITE); 229 if (error) 230 return error; 231 } 232 } 233 234 if ((ia_valid & ATTR_MODE)) { 235 umode_t amode = attr->ia_mode; 236 /* Flag setting protected by i_mutex */ 237 if (is_sxid(amode)) 238 inode->i_flags &= ~S_NOSEC; 239 } 240 241 now = current_time(inode); 242 243 attr->ia_ctime = now; 244 if (!(ia_valid & ATTR_ATIME_SET)) 245 attr->ia_atime = now; 246 if (!(ia_valid & ATTR_MTIME_SET)) 247 attr->ia_mtime = now; 248 if (ia_valid & ATTR_KILL_PRIV) { 249 error = security_inode_need_killpriv(dentry); 250 if (error < 0) 251 return error; 252 if (error == 0) 253 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; 254 } 255 256 /* 257 * We now pass ATTR_KILL_S*ID to the lower level setattr function so 258 * that the function has the ability to reinterpret a mode change 259 * that's due to these bits. This adds an implicit restriction that 260 * no function will ever call notify_change with both ATTR_MODE and 261 * ATTR_KILL_S*ID set. 262 */ 263 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) && 264 (ia_valid & ATTR_MODE)) 265 BUG(); 266 267 if (ia_valid & ATTR_KILL_SUID) { 268 if (mode & S_ISUID) { 269 ia_valid = attr->ia_valid |= ATTR_MODE; 270 attr->ia_mode = (inode->i_mode & ~S_ISUID); 271 } 272 } 273 if (ia_valid & ATTR_KILL_SGID) { 274 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { 275 if (!(ia_valid & ATTR_MODE)) { 276 ia_valid = attr->ia_valid |= ATTR_MODE; 277 attr->ia_mode = inode->i_mode; 278 } 279 attr->ia_mode &= ~S_ISGID; 280 } 281 } 282 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID))) 283 return 0; 284 285 /* 286 * Verify that uid/gid changes are valid in the target 287 * namespace of the superblock. 288 */ 289 if (ia_valid & ATTR_UID && 290 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid)) 291 return -EOVERFLOW; 292 if (ia_valid & ATTR_GID && 293 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid)) 294 return -EOVERFLOW; 295 296 /* Don't allow modifications of files with invalid uids or 297 * gids unless those uids & gids are being made valid. 298 */ 299 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid)) 300 return -EOVERFLOW; 301 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid)) 302 return -EOVERFLOW; 303 304 error = security_inode_setattr(dentry, attr); 305 if (error) 306 return error; 307 error = try_break_deleg(inode, delegated_inode); 308 if (error) 309 return error; 310 311 if (inode->i_op->setattr) 312 error = inode->i_op->setattr(dentry, attr); 313 else 314 error = simple_setattr(dentry, attr); 315 316 if (!error) { 317 fsnotify_change(dentry, ia_valid); 318 ima_inode_post_setattr(dentry); 319 evm_inode_post_setattr(dentry, ia_valid); 320 } 321 322 return error; 323 } 324 EXPORT_SYMBOL(notify_change); 325