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Linux/fs/attr.c

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

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