1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Filesystem access-by-fd.
3 *
4 * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #include <linux/fs_context.h>
9 #include <linux/fs_parser.h>
10 #include <linux/slab.h>
11 #include <linux/uaccess.h>
12 #include <linux/syscalls.h>
13 #include <linux/security.h>
14 #include <linux/anon_inodes.h>
15 #include <linux/namei.h>
16 #include <linux/file.h>
17 #include <uapi/linux/mount.h>
18 #include "internal.h"
19 #include "mount.h"
20
21 /*
22 * Allow the user to read back any error, warning or informational messages.
23 */
fscontext_read(struct file * file,char __user * _buf,size_t len,loff_t * pos)24 static ssize_t fscontext_read(struct file *file,
25 char __user *_buf, size_t len, loff_t *pos)
26 {
27 struct fs_context *fc = file->private_data;
28 struct fc_log *log = fc->log.log;
29 unsigned int logsize = ARRAY_SIZE(log->buffer);
30 ssize_t ret;
31 char *p;
32 bool need_free;
33 int index, n;
34
35 ret = mutex_lock_interruptible(&fc->uapi_mutex);
36 if (ret < 0)
37 return ret;
38
39 if (log->head == log->tail) {
40 mutex_unlock(&fc->uapi_mutex);
41 return -ENODATA;
42 }
43
44 index = log->tail & (logsize - 1);
45 p = log->buffer[index];
46 need_free = log->need_free & (1 << index);
47 log->buffer[index] = NULL;
48 log->need_free &= ~(1 << index);
49 log->tail++;
50 mutex_unlock(&fc->uapi_mutex);
51
52 ret = -EMSGSIZE;
53 n = strlen(p);
54 if (n > len)
55 goto err_free;
56 ret = -EFAULT;
57 if (copy_to_user(_buf, p, n) != 0)
58 goto err_free;
59 ret = n;
60
61 err_free:
62 if (need_free)
63 kfree(p);
64 return ret;
65 }
66
fscontext_release(struct inode * inode,struct file * file)67 static int fscontext_release(struct inode *inode, struct file *file)
68 {
69 struct fs_context *fc = file->private_data;
70
71 if (fc) {
72 file->private_data = NULL;
73 put_fs_context(fc);
74 }
75 return 0;
76 }
77
78 const struct file_operations fscontext_fops = {
79 .read = fscontext_read,
80 .release = fscontext_release,
81 };
82
83 /*
84 * Attach a filesystem context to a file and an fd.
85 */
fscontext_create_fd(struct fs_context * fc,unsigned int o_flags)86 static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
87 {
88 int fd;
89
90 fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
91 O_RDWR | o_flags);
92 if (fd < 0)
93 put_fs_context(fc);
94 return fd;
95 }
96
fscontext_alloc_log(struct fs_context * fc)97 static int fscontext_alloc_log(struct fs_context *fc)
98 {
99 fc->log.log = kzalloc(sizeof(*fc->log.log), GFP_KERNEL);
100 if (!fc->log.log)
101 return -ENOMEM;
102 refcount_set(&fc->log.log->usage, 1);
103 fc->log.log->owner = fc->fs_type->owner;
104 return 0;
105 }
106
107 /*
108 * Open a filesystem by name so that it can be configured for mounting.
109 *
110 * We are allowed to specify a container in which the filesystem will be
111 * opened, thereby indicating which namespaces will be used (notably, which
112 * network namespace will be used for network filesystems).
113 */
SYSCALL_DEFINE2(fsopen,const char __user *,_fs_name,unsigned int,flags)114 SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
115 {
116 struct file_system_type *fs_type;
117 struct fs_context *fc;
118 const char *fs_name;
119 int ret;
120
121 if (!may_mount())
122 return -EPERM;
123
124 if (flags & ~FSOPEN_CLOEXEC)
125 return -EINVAL;
126
127 fs_name = strndup_user(_fs_name, PAGE_SIZE);
128 if (IS_ERR(fs_name))
129 return PTR_ERR(fs_name);
130
131 fs_type = get_fs_type(fs_name);
132 kfree(fs_name);
133 if (!fs_type)
134 return -ENODEV;
135
136 fc = fs_context_for_mount(fs_type, 0);
137 put_filesystem(fs_type);
138 if (IS_ERR(fc))
139 return PTR_ERR(fc);
140
141 fc->phase = FS_CONTEXT_CREATE_PARAMS;
142
143 ret = fscontext_alloc_log(fc);
144 if (ret < 0)
145 goto err_fc;
146
147 return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
148
149 err_fc:
150 put_fs_context(fc);
151 return ret;
152 }
153
154 /*
155 * Pick a superblock into a context for reconfiguration.
156 */
SYSCALL_DEFINE3(fspick,int,dfd,const char __user *,path,unsigned int,flags)157 SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
158 {
159 struct fs_context *fc;
160 struct path target;
161 unsigned int lookup_flags;
162 int ret;
163
164 if (!may_mount())
165 return -EPERM;
166
167 if ((flags & ~(FSPICK_CLOEXEC |
168 FSPICK_SYMLINK_NOFOLLOW |
169 FSPICK_NO_AUTOMOUNT |
170 FSPICK_EMPTY_PATH)) != 0)
171 return -EINVAL;
172
173 lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
174 if (flags & FSPICK_SYMLINK_NOFOLLOW)
175 lookup_flags &= ~LOOKUP_FOLLOW;
176 if (flags & FSPICK_NO_AUTOMOUNT)
177 lookup_flags &= ~LOOKUP_AUTOMOUNT;
178 if (flags & FSPICK_EMPTY_PATH)
179 lookup_flags |= LOOKUP_EMPTY;
180 ret = user_path_at(dfd, path, lookup_flags, &target);
181 if (ret < 0)
182 goto err;
183
184 ret = -EINVAL;
185 if (target.mnt->mnt_root != target.dentry)
186 goto err_path;
187
188 fc = fs_context_for_reconfigure(target.dentry, 0, 0);
189 if (IS_ERR(fc)) {
190 ret = PTR_ERR(fc);
191 goto err_path;
192 }
193
194 fc->phase = FS_CONTEXT_RECONF_PARAMS;
195
196 ret = fscontext_alloc_log(fc);
197 if (ret < 0)
198 goto err_fc;
199
200 path_put(&target);
201 return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);
202
203 err_fc:
204 put_fs_context(fc);
205 err_path:
206 path_put(&target);
207 err:
208 return ret;
209 }
210
vfs_cmd_create(struct fs_context * fc,bool exclusive)211 static int vfs_cmd_create(struct fs_context *fc, bool exclusive)
212 {
213 struct super_block *sb;
214 int ret;
215
216 if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
217 return -EBUSY;
218
219 if (!mount_capable(fc))
220 return -EPERM;
221
222 fc->phase = FS_CONTEXT_CREATING;
223 fc->exclusive = exclusive;
224
225 ret = vfs_get_tree(fc);
226 if (ret) {
227 fc->phase = FS_CONTEXT_FAILED;
228 return ret;
229 }
230
231 sb = fc->root->d_sb;
232 ret = security_sb_kern_mount(sb);
233 if (unlikely(ret)) {
234 fc_drop_locked(fc);
235 fc->phase = FS_CONTEXT_FAILED;
236 return ret;
237 }
238
239 /* vfs_get_tree() callchains will have grabbed @s_umount */
240 up_write(&sb->s_umount);
241 fc->phase = FS_CONTEXT_AWAITING_MOUNT;
242 return 0;
243 }
244
vfs_cmd_reconfigure(struct fs_context * fc)245 static int vfs_cmd_reconfigure(struct fs_context *fc)
246 {
247 struct super_block *sb;
248 int ret;
249
250 if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
251 return -EBUSY;
252
253 fc->phase = FS_CONTEXT_RECONFIGURING;
254
255 sb = fc->root->d_sb;
256 if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
257 fc->phase = FS_CONTEXT_FAILED;
258 return -EPERM;
259 }
260
261 down_write(&sb->s_umount);
262 ret = reconfigure_super(fc);
263 up_write(&sb->s_umount);
264 if (ret) {
265 fc->phase = FS_CONTEXT_FAILED;
266 return ret;
267 }
268
269 vfs_clean_context(fc);
270 return 0;
271 }
272
273 /*
274 * Check the state and apply the configuration. Note that this function is
275 * allowed to 'steal' the value by setting param->xxx to NULL before returning.
276 */
vfs_fsconfig_locked(struct fs_context * fc,int cmd,struct fs_parameter * param)277 static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
278 struct fs_parameter *param)
279 {
280 int ret;
281
282 ret = finish_clean_context(fc);
283 if (ret)
284 return ret;
285 switch (cmd) {
286 case FSCONFIG_CMD_CREATE:
287 return vfs_cmd_create(fc, false);
288 case FSCONFIG_CMD_CREATE_EXCL:
289 return vfs_cmd_create(fc, true);
290 case FSCONFIG_CMD_RECONFIGURE:
291 return vfs_cmd_reconfigure(fc);
292 default:
293 if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
294 fc->phase != FS_CONTEXT_RECONF_PARAMS)
295 return -EBUSY;
296
297 return vfs_parse_fs_param(fc, param);
298 }
299 }
300
301 /**
302 * sys_fsconfig - Set parameters and trigger actions on a context
303 * @fd: The filesystem context to act upon
304 * @cmd: The action to take
305 * @_key: Where appropriate, the parameter key to set
306 * @_value: Where appropriate, the parameter value to set
307 * @aux: Additional information for the value
308 *
309 * This system call is used to set parameters on a context, including
310 * superblock settings, data source and security labelling.
311 *
312 * Actions include triggering the creation of a superblock and the
313 * reconfiguration of the superblock attached to the specified context.
314 *
315 * When setting a parameter, @cmd indicates the type of value being proposed
316 * and @_key indicates the parameter to be altered.
317 *
318 * @_value and @aux are used to specify the value, should a value be required:
319 *
320 * (*) fsconfig_set_flag: No value is specified. The parameter must be boolean
321 * in nature. The key may be prefixed with "no" to invert the
322 * setting. @_value must be NULL and @aux must be 0.
323 *
324 * (*) fsconfig_set_string: A string value is specified. The parameter can be
325 * expecting boolean, integer, string or take a path. A conversion to an
326 * appropriate type will be attempted (which may include looking up as a
327 * path). @_value points to a NUL-terminated string and @aux must be 0.
328 *
329 * (*) fsconfig_set_binary: A binary blob is specified. @_value points to the
330 * blob and @aux indicates its size. The parameter must be expecting a
331 * blob.
332 *
333 * (*) fsconfig_set_path: A non-empty path is specified. The parameter must be
334 * expecting a path object. @_value points to a NUL-terminated string that
335 * is the path and @aux is a file descriptor at which to start a relative
336 * lookup or AT_FDCWD.
337 *
338 * (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
339 * implied.
340 *
341 * (*) fsconfig_set_fd: An open file descriptor is specified. @_value must be
342 * NULL and @aux indicates the file descriptor.
343 */
SYSCALL_DEFINE5(fsconfig,int,fd,unsigned int,cmd,const char __user *,_key,const void __user *,_value,int,aux)344 SYSCALL_DEFINE5(fsconfig,
345 int, fd,
346 unsigned int, cmd,
347 const char __user *, _key,
348 const void __user *, _value,
349 int, aux)
350 {
351 struct fs_context *fc;
352 int ret;
353 int lookup_flags = 0;
354
355 struct fs_parameter param = {
356 .type = fs_value_is_undefined,
357 };
358
359 if (fd < 0)
360 return -EINVAL;
361
362 switch (cmd) {
363 case FSCONFIG_SET_FLAG:
364 if (!_key || _value || aux)
365 return -EINVAL;
366 break;
367 case FSCONFIG_SET_STRING:
368 if (!_key || !_value || aux)
369 return -EINVAL;
370 break;
371 case FSCONFIG_SET_BINARY:
372 if (!_key || !_value || aux <= 0 || aux > 1024 * 1024)
373 return -EINVAL;
374 break;
375 case FSCONFIG_SET_PATH:
376 case FSCONFIG_SET_PATH_EMPTY:
377 if (!_key || !_value || (aux != AT_FDCWD && aux < 0))
378 return -EINVAL;
379 break;
380 case FSCONFIG_SET_FD:
381 if (!_key || _value || aux < 0)
382 return -EINVAL;
383 break;
384 case FSCONFIG_CMD_CREATE:
385 case FSCONFIG_CMD_CREATE_EXCL:
386 case FSCONFIG_CMD_RECONFIGURE:
387 if (_key || _value || aux)
388 return -EINVAL;
389 break;
390 default:
391 return -EOPNOTSUPP;
392 }
393
394 CLASS(fd, f)(fd);
395 if (fd_empty(f))
396 return -EBADF;
397 if (fd_file(f)->f_op != &fscontext_fops)
398 return -EINVAL;
399
400 fc = fd_file(f)->private_data;
401 if (fc->ops == &legacy_fs_context_ops) {
402 switch (cmd) {
403 case FSCONFIG_SET_BINARY:
404 case FSCONFIG_SET_PATH:
405 case FSCONFIG_SET_PATH_EMPTY:
406 case FSCONFIG_SET_FD:
407 case FSCONFIG_CMD_CREATE_EXCL:
408 return -EOPNOTSUPP;
409 }
410 }
411
412 if (_key) {
413 param.key = strndup_user(_key, 256);
414 if (IS_ERR(param.key))
415 return PTR_ERR(param.key);
416 }
417
418 switch (cmd) {
419 case FSCONFIG_SET_FLAG:
420 param.type = fs_value_is_flag;
421 break;
422 case FSCONFIG_SET_STRING:
423 param.type = fs_value_is_string;
424 param.string = strndup_user(_value, 256);
425 if (IS_ERR(param.string)) {
426 ret = PTR_ERR(param.string);
427 goto out_key;
428 }
429 param.size = strlen(param.string);
430 break;
431 case FSCONFIG_SET_BINARY:
432 param.type = fs_value_is_blob;
433 param.size = aux;
434 param.blob = memdup_user_nul(_value, aux);
435 if (IS_ERR(param.blob)) {
436 ret = PTR_ERR(param.blob);
437 goto out_key;
438 }
439 break;
440 case FSCONFIG_SET_PATH_EMPTY:
441 lookup_flags = LOOKUP_EMPTY;
442 fallthrough;
443 case FSCONFIG_SET_PATH:
444 param.type = fs_value_is_filename;
445 param.name = getname_flags(_value, lookup_flags);
446 if (IS_ERR(param.name)) {
447 ret = PTR_ERR(param.name);
448 goto out_key;
449 }
450 param.dirfd = aux;
451 param.size = strlen(param.name->name);
452 break;
453 case FSCONFIG_SET_FD:
454 param.type = fs_value_is_file;
455 ret = -EBADF;
456 param.file = fget(aux);
457 if (!param.file)
458 goto out_key;
459 param.dirfd = aux;
460 break;
461 default:
462 break;
463 }
464
465 ret = mutex_lock_interruptible(&fc->uapi_mutex);
466 if (ret == 0) {
467 ret = vfs_fsconfig_locked(fc, cmd, ¶m);
468 mutex_unlock(&fc->uapi_mutex);
469 }
470
471 /* Clean up the our record of any value that we obtained from
472 * userspace. Note that the value may have been stolen by the LSM or
473 * filesystem, in which case the value pointer will have been cleared.
474 */
475 switch (cmd) {
476 case FSCONFIG_SET_STRING:
477 case FSCONFIG_SET_BINARY:
478 kfree(param.string);
479 break;
480 case FSCONFIG_SET_PATH:
481 case FSCONFIG_SET_PATH_EMPTY:
482 if (param.name)
483 putname(param.name);
484 break;
485 case FSCONFIG_SET_FD:
486 if (param.file)
487 fput(param.file);
488 break;
489 default:
490 break;
491 }
492 out_key:
493 kfree(param.key);
494 return ret;
495 }
496