Merge tag 'gcc-plugins-v4.9-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git...
[cascardo/linux.git] / fs / overlayfs / inode.c
1 /*
2  *
3  * Copyright (C) 2011 Novell Inc.
4  *
5  * This program is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License version 2 as published by
7  * the Free Software Foundation.
8  */
9
10 #include <linux/fs.h>
11 #include <linux/slab.h>
12 #include <linux/xattr.h>
13 #include <linux/posix_acl.h>
14 #include "overlayfs.h"
15
16 static int ovl_copy_up_truncate(struct dentry *dentry)
17 {
18         int err;
19         struct dentry *parent;
20         struct kstat stat;
21         struct path lowerpath;
22         const struct cred *old_cred;
23
24         parent = dget_parent(dentry);
25         err = ovl_copy_up(parent);
26         if (err)
27                 goto out_dput_parent;
28
29         ovl_path_lower(dentry, &lowerpath);
30
31         old_cred = ovl_override_creds(dentry->d_sb);
32         err = vfs_getattr(&lowerpath, &stat);
33         if (!err) {
34                 stat.size = 0;
35                 err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
36         }
37         revert_creds(old_cred);
38
39 out_dput_parent:
40         dput(parent);
41         return err;
42 }
43
44 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
45 {
46         int err;
47         struct dentry *upperdentry;
48         const struct cred *old_cred;
49
50         /*
51          * Check for permissions before trying to copy-up.  This is redundant
52          * since it will be rechecked later by ->setattr() on upper dentry.  But
53          * without this, copy-up can be triggered by just about anybody.
54          *
55          * We don't initialize inode->size, which just means that
56          * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
57          * check for a swapfile (which this won't be anyway).
58          */
59         err = setattr_prepare(dentry, attr);
60         if (err)
61                 return err;
62
63         err = ovl_want_write(dentry);
64         if (err)
65                 goto out;
66
67         if (attr->ia_valid & ATTR_SIZE) {
68                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
69
70                 err = -ETXTBSY;
71                 if (atomic_read(&realinode->i_writecount) < 0)
72                         goto out_drop_write;
73         }
74
75         err = ovl_copy_up(dentry);
76         if (!err) {
77                 struct inode *winode = NULL;
78
79                 upperdentry = ovl_dentry_upper(dentry);
80
81                 if (attr->ia_valid & ATTR_SIZE) {
82                         winode = d_inode(upperdentry);
83                         err = get_write_access(winode);
84                         if (err)
85                                 goto out_drop_write;
86                 }
87
88                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
89                         attr->ia_valid &= ~ATTR_MODE;
90
91                 inode_lock(upperdentry->d_inode);
92                 old_cred = ovl_override_creds(dentry->d_sb);
93                 err = notify_change(upperdentry, attr, NULL);
94                 revert_creds(old_cred);
95                 if (!err)
96                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
97                 inode_unlock(upperdentry->d_inode);
98
99                 if (winode)
100                         put_write_access(winode);
101         }
102 out_drop_write:
103         ovl_drop_write(dentry);
104 out:
105         return err;
106 }
107
108 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
109                          struct kstat *stat)
110 {
111         struct path realpath;
112         const struct cred *old_cred;
113         int err;
114
115         ovl_path_real(dentry, &realpath);
116         old_cred = ovl_override_creds(dentry->d_sb);
117         err = vfs_getattr(&realpath, stat);
118         revert_creds(old_cred);
119         return err;
120 }
121
122 int ovl_permission(struct inode *inode, int mask)
123 {
124         bool is_upper;
125         struct inode *realinode = ovl_inode_real(inode, &is_upper);
126         const struct cred *old_cred;
127         int err;
128
129         /* Careful in RCU walk mode */
130         if (!realinode) {
131                 WARN_ON(!(mask & MAY_NOT_BLOCK));
132                 return -ECHILD;
133         }
134
135         /*
136          * Check overlay inode with the creds of task and underlying inode
137          * with creds of mounter
138          */
139         err = generic_permission(inode, mask);
140         if (err)
141                 return err;
142
143         old_cred = ovl_override_creds(inode->i_sb);
144         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
145                 mask &= ~(MAY_WRITE | MAY_APPEND);
146                 /* Make sure mounter can read file for copy up later */
147                 mask |= MAY_READ;
148         }
149         err = inode_permission(realinode, mask);
150         revert_creds(old_cred);
151
152         return err;
153 }
154
155 static const char *ovl_get_link(struct dentry *dentry,
156                                 struct inode *inode,
157                                 struct delayed_call *done)
158 {
159         const struct cred *old_cred;
160         const char *p;
161
162         if (!dentry)
163                 return ERR_PTR(-ECHILD);
164
165         old_cred = ovl_override_creds(dentry->d_sb);
166         p = vfs_get_link(ovl_dentry_real(dentry), done);
167         revert_creds(old_cred);
168         return p;
169 }
170
171 bool ovl_is_private_xattr(const char *name)
172 {
173         return strncmp(name, OVL_XATTR_PREFIX,
174                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
175 }
176
177 int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
178                   size_t size, int flags)
179 {
180         int err;
181         struct path realpath;
182         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
183         const struct cred *old_cred;
184
185         err = ovl_want_write(dentry);
186         if (err)
187                 goto out;
188
189         if (!value && !OVL_TYPE_UPPER(type)) {
190                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
191                 if (err < 0)
192                         goto out_drop_write;
193         }
194
195         err = ovl_copy_up(dentry);
196         if (err)
197                 goto out_drop_write;
198
199         if (!OVL_TYPE_UPPER(type))
200                 ovl_path_upper(dentry, &realpath);
201
202         old_cred = ovl_override_creds(dentry->d_sb);
203         if (value)
204                 err = vfs_setxattr(realpath.dentry, name, value, size, flags);
205         else {
206                 WARN_ON(flags != XATTR_REPLACE);
207                 err = vfs_removexattr(realpath.dentry, name);
208         }
209         revert_creds(old_cred);
210
211 out_drop_write:
212         ovl_drop_write(dentry);
213 out:
214         return err;
215 }
216
217 int ovl_xattr_get(struct dentry *dentry, const char *name,
218                   void *value, size_t size)
219 {
220         struct dentry *realdentry = ovl_dentry_real(dentry);
221         ssize_t res;
222         const struct cred *old_cred;
223
224         old_cred = ovl_override_creds(dentry->d_sb);
225         res = vfs_getxattr(realdentry, name, value, size);
226         revert_creds(old_cred);
227         return res;
228 }
229
230 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
231 {
232         struct dentry *realdentry = ovl_dentry_real(dentry);
233         ssize_t res;
234         size_t len;
235         char *s;
236         const struct cred *old_cred;
237
238         old_cred = ovl_override_creds(dentry->d_sb);
239         res = vfs_listxattr(realdentry, list, size);
240         revert_creds(old_cred);
241         if (res <= 0 || size == 0)
242                 return res;
243
244         /* filter out private xattrs */
245         for (s = list, len = res; len;) {
246                 size_t slen = strnlen(s, len) + 1;
247
248                 /* underlying fs providing us with an broken xattr list? */
249                 if (WARN_ON(slen > len))
250                         return -EIO;
251
252                 len -= slen;
253                 if (ovl_is_private_xattr(s)) {
254                         res -= slen;
255                         memmove(s, s + slen, len);
256                 } else {
257                         s += slen;
258                 }
259         }
260
261         return res;
262 }
263
264 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
265 {
266         struct inode *realinode = ovl_inode_real(inode, NULL);
267         const struct cred *old_cred;
268         struct posix_acl *acl;
269
270         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
271                 return NULL;
272
273         if (!realinode->i_op->get_acl)
274                 return NULL;
275
276         old_cred = ovl_override_creds(inode->i_sb);
277         acl = get_acl(realinode, type);
278         revert_creds(old_cred);
279
280         return acl;
281 }
282
283 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
284                                   struct dentry *realdentry)
285 {
286         if (OVL_TYPE_UPPER(type))
287                 return false;
288
289         if (special_file(realdentry->d_inode->i_mode))
290                 return false;
291
292         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
293                 return false;
294
295         return true;
296 }
297
298 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
299 {
300         int err = 0;
301         struct path realpath;
302         enum ovl_path_type type;
303
304         type = ovl_path_real(dentry, &realpath);
305         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
306                 err = ovl_want_write(dentry);
307                 if (!err) {
308                         if (file_flags & O_TRUNC)
309                                 err = ovl_copy_up_truncate(dentry);
310                         else
311                                 err = ovl_copy_up(dentry);
312                         ovl_drop_write(dentry);
313                 }
314         }
315
316         return err;
317 }
318
319 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
320 {
321         struct dentry *alias;
322         struct path upperpath;
323
324         if (!(flags & S_ATIME))
325                 return 0;
326
327         alias = d_find_any_alias(inode);
328         if (!alias)
329                 return 0;
330
331         ovl_path_upper(alias, &upperpath);
332         if (upperpath.dentry) {
333                 touch_atime(&upperpath);
334                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
335         }
336
337         dput(alias);
338
339         return 0;
340 }
341
342 static const struct inode_operations ovl_file_inode_operations = {
343         .setattr        = ovl_setattr,
344         .permission     = ovl_permission,
345         .getattr        = ovl_getattr,
346         .listxattr      = ovl_listxattr,
347         .get_acl        = ovl_get_acl,
348         .update_time    = ovl_update_time,
349 };
350
351 static const struct inode_operations ovl_symlink_inode_operations = {
352         .setattr        = ovl_setattr,
353         .get_link       = ovl_get_link,
354         .readlink       = generic_readlink,
355         .getattr        = ovl_getattr,
356         .listxattr      = ovl_listxattr,
357         .update_time    = ovl_update_time,
358 };
359
360 static void ovl_fill_inode(struct inode *inode, umode_t mode)
361 {
362         inode->i_ino = get_next_ino();
363         inode->i_mode = mode;
364         inode->i_flags |= S_NOCMTIME;
365 #ifdef CONFIG_FS_POSIX_ACL
366         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
367 #endif
368
369         mode &= S_IFMT;
370         switch (mode) {
371         case S_IFDIR:
372                 inode->i_op = &ovl_dir_inode_operations;
373                 inode->i_fop = &ovl_dir_operations;
374                 break;
375
376         case S_IFLNK:
377                 inode->i_op = &ovl_symlink_inode_operations;
378                 break;
379
380         default:
381                 WARN(1, "illegal file type: %i\n", mode);
382                 /* Fall through */
383
384         case S_IFREG:
385         case S_IFSOCK:
386         case S_IFBLK:
387         case S_IFCHR:
388         case S_IFIFO:
389                 inode->i_op = &ovl_file_inode_operations;
390                 break;
391         }
392 }
393
394 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
395 {
396         struct inode *inode;
397
398         inode = new_inode(sb);
399         if (inode)
400                 ovl_fill_inode(inode, mode);
401
402         return inode;
403 }
404
405 static int ovl_inode_test(struct inode *inode, void *data)
406 {
407         return ovl_inode_real(inode, NULL) == data;
408 }
409
410 static int ovl_inode_set(struct inode *inode, void *data)
411 {
412         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
413         return 0;
414 }
415
416 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
417
418 {
419         struct inode *inode;
420
421         inode = iget5_locked(sb, (unsigned long) realinode,
422                              ovl_inode_test, ovl_inode_set, realinode);
423         if (inode && inode->i_state & I_NEW) {
424                 ovl_fill_inode(inode, realinode->i_mode);
425                 set_nlink(inode, realinode->i_nlink);
426                 unlock_new_inode(inode);
427         }
428
429         return inode;
430 }