xref: /openbmc/linux/fs/fsopen.c (revision 22ed7ecd)
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 (!may_mount())
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 (!may_mount())
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 
vfs_cmd_create(struct fs_context * fc,bool exclusive)212 static int vfs_cmd_create(struct fs_context *fc, bool exclusive)
213 {
214 	struct super_block *sb;
215 	int ret;
216 
217 	if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
218 		return -EBUSY;
219 
220 	if (!mount_capable(fc))
221 		return -EPERM;
222 
223 	/* require the new mount api */
224 	if (exclusive && fc->ops == &legacy_fs_context_ops)
225 		return -EOPNOTSUPP;
226 
227 	fc->phase = FS_CONTEXT_CREATING;
228 	fc->exclusive = exclusive;
229 
230 	ret = vfs_get_tree(fc);
231 	if (ret) {
232 		fc->phase = FS_CONTEXT_FAILED;
233 		return ret;
234 	}
235 
236 	sb = fc->root->d_sb;
237 	ret = security_sb_kern_mount(sb);
238 	if (unlikely(ret)) {
239 		fc_drop_locked(fc);
240 		fc->phase = FS_CONTEXT_FAILED;
241 		return ret;
242 	}
243 
244 	/* vfs_get_tree() callchains will have grabbed @s_umount */
245 	up_write(&sb->s_umount);
246 	fc->phase = FS_CONTEXT_AWAITING_MOUNT;
247 	return 0;
248 }
249 
vfs_cmd_reconfigure(struct fs_context * fc)250 static int vfs_cmd_reconfigure(struct fs_context *fc)
251 {
252 	struct super_block *sb;
253 	int ret;
254 
255 	if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
256 		return -EBUSY;
257 
258 	fc->phase = FS_CONTEXT_RECONFIGURING;
259 
260 	sb = fc->root->d_sb;
261 	if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
262 		fc->phase = FS_CONTEXT_FAILED;
263 		return -EPERM;
264 	}
265 
266 	down_write(&sb->s_umount);
267 	ret = reconfigure_super(fc);
268 	up_write(&sb->s_umount);
269 	if (ret) {
270 		fc->phase = FS_CONTEXT_FAILED;
271 		return ret;
272 	}
273 
274 	vfs_clean_context(fc);
275 	return 0;
276 }
277 
278 /*
279  * Check the state and apply the configuration.  Note that this function is
280  * allowed to 'steal' the value by setting param->xxx to NULL before returning.
281  */
vfs_fsconfig_locked(struct fs_context * fc,int cmd,struct fs_parameter * param)282 static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
283 			       struct fs_parameter *param)
284 {
285 	int ret;
286 
287 	ret = finish_clean_context(fc);
288 	if (ret)
289 		return ret;
290 	switch (cmd) {
291 	case FSCONFIG_CMD_CREATE:
292 		return vfs_cmd_create(fc, false);
293 	case FSCONFIG_CMD_CREATE_EXCL:
294 		return vfs_cmd_create(fc, true);
295 	case FSCONFIG_CMD_RECONFIGURE:
296 		return vfs_cmd_reconfigure(fc);
297 	default:
298 		if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
299 		    fc->phase != FS_CONTEXT_RECONF_PARAMS)
300 			return -EBUSY;
301 
302 		return vfs_parse_fs_param(fc, param);
303 	}
304 }
305 
306 /**
307  * sys_fsconfig - Set parameters and trigger actions on a context
308  * @fd: The filesystem context to act upon
309  * @cmd: The action to take
310  * @_key: Where appropriate, the parameter key to set
311  * @_value: Where appropriate, the parameter value to set
312  * @aux: Additional information for the value
313  *
314  * This system call is used to set parameters on a context, including
315  * superblock settings, data source and security labelling.
316  *
317  * Actions include triggering the creation of a superblock and the
318  * reconfiguration of the superblock attached to the specified context.
319  *
320  * When setting a parameter, @cmd indicates the type of value being proposed
321  * and @_key indicates the parameter to be altered.
322  *
323  * @_value and @aux are used to specify the value, should a value be required:
324  *
325  * (*) fsconfig_set_flag: No value is specified.  The parameter must be boolean
326  *     in nature.  The key may be prefixed with "no" to invert the
327  *     setting. @_value must be NULL and @aux must be 0.
328  *
329  * (*) fsconfig_set_string: A string value is specified.  The parameter can be
330  *     expecting boolean, integer, string or take a path.  A conversion to an
331  *     appropriate type will be attempted (which may include looking up as a
332  *     path).  @_value points to a NUL-terminated string and @aux must be 0.
333  *
334  * (*) fsconfig_set_binary: A binary blob is specified.  @_value points to the
335  *     blob and @aux indicates its size.  The parameter must be expecting a
336  *     blob.
337  *
338  * (*) fsconfig_set_path: A non-empty path is specified.  The parameter must be
339  *     expecting a path object.  @_value points to a NUL-terminated string that
340  *     is the path and @aux is a file descriptor at which to start a relative
341  *     lookup or AT_FDCWD.
342  *
343  * (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
344  *     implied.
345  *
346  * (*) fsconfig_set_fd: An open file descriptor is specified.  @_value must be
347  *     NULL and @aux indicates the file descriptor.
348  */
SYSCALL_DEFINE5(fsconfig,int,fd,unsigned int,cmd,const char __user *,_key,const void __user *,_value,int,aux)349 SYSCALL_DEFINE5(fsconfig,
350 		int, fd,
351 		unsigned int, cmd,
352 		const char __user *, _key,
353 		const void __user *, _value,
354 		int, aux)
355 {
356 	struct fs_context *fc;
357 	struct fd f;
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 	f = fdget(fd);
401 	if (!f.file)
402 		return -EBADF;
403 	ret = -EINVAL;
404 	if (f.file->f_op != &fscontext_fops)
405 		goto out_f;
406 
407 	fc = f.file->private_data;
408 	if (fc->ops == &legacy_fs_context_ops) {
409 		switch (cmd) {
410 		case FSCONFIG_SET_BINARY:
411 		case FSCONFIG_SET_PATH:
412 		case FSCONFIG_SET_PATH_EMPTY:
413 		case FSCONFIG_SET_FD:
414 			ret = -EOPNOTSUPP;
415 			goto out_f;
416 		}
417 	}
418 
419 	if (_key) {
420 		param.key = strndup_user(_key, 256);
421 		if (IS_ERR(param.key)) {
422 			ret = PTR_ERR(param.key);
423 			goto out_f;
424 		}
425 	}
426 
427 	switch (cmd) {
428 	case FSCONFIG_SET_FLAG:
429 		param.type = fs_value_is_flag;
430 		break;
431 	case FSCONFIG_SET_STRING:
432 		param.type = fs_value_is_string;
433 		param.string = strndup_user(_value, 256);
434 		if (IS_ERR(param.string)) {
435 			ret = PTR_ERR(param.string);
436 			goto out_key;
437 		}
438 		param.size = strlen(param.string);
439 		break;
440 	case FSCONFIG_SET_BINARY:
441 		param.type = fs_value_is_blob;
442 		param.size = aux;
443 		param.blob = memdup_user_nul(_value, aux);
444 		if (IS_ERR(param.blob)) {
445 			ret = PTR_ERR(param.blob);
446 			goto out_key;
447 		}
448 		break;
449 	case FSCONFIG_SET_PATH_EMPTY:
450 		lookup_flags = LOOKUP_EMPTY;
451 		fallthrough;
452 	case FSCONFIG_SET_PATH:
453 		param.type = fs_value_is_filename;
454 		param.name = getname_flags(_value, lookup_flags, NULL);
455 		if (IS_ERR(param.name)) {
456 			ret = PTR_ERR(param.name);
457 			goto out_key;
458 		}
459 		param.dirfd = aux;
460 		param.size = strlen(param.name->name);
461 		break;
462 	case FSCONFIG_SET_FD:
463 		param.type = fs_value_is_file;
464 		ret = -EBADF;
465 		param.file = fget(aux);
466 		if (!param.file)
467 			goto out_key;
468 		break;
469 	default:
470 		break;
471 	}
472 
473 	ret = mutex_lock_interruptible(&fc->uapi_mutex);
474 	if (ret == 0) {
475 		ret = vfs_fsconfig_locked(fc, cmd, &param);
476 		mutex_unlock(&fc->uapi_mutex);
477 	}
478 
479 	/* Clean up the our record of any value that we obtained from
480 	 * userspace.  Note that the value may have been stolen by the LSM or
481 	 * filesystem, in which case the value pointer will have been cleared.
482 	 */
483 	switch (cmd) {
484 	case FSCONFIG_SET_STRING:
485 	case FSCONFIG_SET_BINARY:
486 		kfree(param.string);
487 		break;
488 	case FSCONFIG_SET_PATH:
489 	case FSCONFIG_SET_PATH_EMPTY:
490 		if (param.name)
491 			putname(param.name);
492 		break;
493 	case FSCONFIG_SET_FD:
494 		if (param.file)
495 			fput(param.file);
496 		break;
497 	default:
498 		break;
499 	}
500 out_key:
501 	kfree(param.key);
502 out_f:
503 	fdput(f);
504 	return ret;
505 }
506