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