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