xref: /openbmc/linux/fs/fs_context.c (revision d003d772) 
1 /* Provide a way to create a superblock configuration context within the kernel
2  * that allows a superblock to be set up prior to mounting.
3  *
4  * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
5  * Written by David Howells (dhowells@redhat.com)
6  *
7  * This program is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU General Public Licence
9  * as published by the Free Software Foundation; either version
10  * 2 of the Licence, or (at your option) any later version.
11  */
12 
13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
14 #include <linux/fs_context.h>
15 #include <linux/fs_parser.h>
16 #include <linux/fs.h>
17 #include <linux/mount.h>
18 #include <linux/nsproxy.h>
19 #include <linux/slab.h>
20 #include <linux/magic.h>
21 #include <linux/security.h>
22 #include <linux/mnt_namespace.h>
23 #include <linux/pid_namespace.h>
24 #include <linux/user_namespace.h>
25 #include <net/net_namespace.h>
26 #include "mount.h"
27 #include "internal.h"
28 
29 enum legacy_fs_param {
30 	LEGACY_FS_UNSET_PARAMS,
31 	LEGACY_FS_MONOLITHIC_PARAMS,
32 	LEGACY_FS_INDIVIDUAL_PARAMS,
33 };
34 
35 struct legacy_fs_context {
36 	char			*legacy_data;	/* Data page for legacy filesystems */
37 	size_t			data_size;
38 	enum legacy_fs_param	param_type;
39 };
40 
41 static int legacy_init_fs_context(struct fs_context *fc);
42 
43 static const struct constant_table common_set_sb_flag[] = {
44 	{ "dirsync",	SB_DIRSYNC },
45 	{ "lazytime",	SB_LAZYTIME },
46 	{ "mand",	SB_MANDLOCK },
47 	{ "posixacl",	SB_POSIXACL },
48 	{ "ro",		SB_RDONLY },
49 	{ "sync",	SB_SYNCHRONOUS },
50 };
51 
52 static const struct constant_table common_clear_sb_flag[] = {
53 	{ "async",	SB_SYNCHRONOUS },
54 	{ "nolazytime",	SB_LAZYTIME },
55 	{ "nomand",	SB_MANDLOCK },
56 	{ "rw",		SB_RDONLY },
57 	{ "silent",	SB_SILENT },
58 };
59 
60 static const char *const forbidden_sb_flag[] = {
61 	"bind",
62 	"dev",
63 	"exec",
64 	"move",
65 	"noatime",
66 	"nodev",
67 	"nodiratime",
68 	"noexec",
69 	"norelatime",
70 	"nostrictatime",
71 	"nosuid",
72 	"private",
73 	"rec",
74 	"relatime",
75 	"remount",
76 	"shared",
77 	"slave",
78 	"strictatime",
79 	"suid",
80 	"unbindable",
81 };
82 
83 /*
84  * Check for a common mount option that manipulates s_flags.
85  */
86 static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
87 {
88 	unsigned int token;
89 	unsigned int i;
90 
91 	for (i = 0; i < ARRAY_SIZE(forbidden_sb_flag); i++)
92 		if (strcmp(key, forbidden_sb_flag[i]) == 0)
93 			return -EINVAL;
94 
95 	token = lookup_constant(common_set_sb_flag, key, 0);
96 	if (token) {
97 		fc->sb_flags |= token;
98 		fc->sb_flags_mask |= token;
99 		return 0;
100 	}
101 
102 	token = lookup_constant(common_clear_sb_flag, key, 0);
103 	if (token) {
104 		fc->sb_flags &= ~token;
105 		fc->sb_flags_mask |= token;
106 		return 0;
107 	}
108 
109 	return -ENOPARAM;
110 }
111 
112 /**
113  * vfs_parse_fs_param - Add a single parameter to a superblock config
114  * @fc: The filesystem context to modify
115  * @param: The parameter
116  *
117  * A single mount option in string form is applied to the filesystem context
118  * being set up.  Certain standard options (for example "ro") are translated
119  * into flag bits without going to the filesystem.  The active security module
120  * is allowed to observe and poach options.  Any other options are passed over
121  * to the filesystem to parse.
122  *
123  * This may be called multiple times for a context.
124  *
125  * Returns 0 on success and a negative error code on failure.  In the event of
126  * failure, supplementary error information may have been set.
127  */
128 int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
129 {
130 	int ret;
131 
132 	if (!param->key)
133 		return invalf(fc, "Unnamed parameter\n");
134 
135 	ret = vfs_parse_sb_flag(fc, param->key);
136 	if (ret != -ENOPARAM)
137 		return ret;
138 
139 	ret = security_fs_context_parse_param(fc, param);
140 	if (ret != -ENOPARAM)
141 		/* Param belongs to the LSM or is disallowed by the LSM; so
142 		 * don't pass to the FS.
143 		 */
144 		return ret;
145 
146 	if (fc->ops->parse_param) {
147 		ret = fc->ops->parse_param(fc, param);
148 		if (ret != -ENOPARAM)
149 			return ret;
150 	}
151 
152 	/* If the filesystem doesn't take any arguments, give it the
153 	 * default handling of source.
154 	 */
155 	if (strcmp(param->key, "source") == 0) {
156 		if (param->type != fs_value_is_string)
157 			return invalf(fc, "VFS: Non-string source");
158 		if (fc->source)
159 			return invalf(fc, "VFS: Multiple sources");
160 		fc->source = param->string;
161 		param->string = NULL;
162 		return 0;
163 	}
164 
165 	return invalf(fc, "%s: Unknown parameter '%s'",
166 		      fc->fs_type->name, param->key);
167 }
168 EXPORT_SYMBOL(vfs_parse_fs_param);
169 
170 /**
171  * vfs_parse_fs_string - Convenience function to just parse a string.
172  */
173 int vfs_parse_fs_string(struct fs_context *fc, const char *key,
174 			const char *value, size_t v_size)
175 {
176 	int ret;
177 
178 	struct fs_parameter param = {
179 		.key	= key,
180 		.type	= fs_value_is_string,
181 		.size	= v_size,
182 	};
183 
184 	if (v_size > 0) {
185 		param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
186 		if (!param.string)
187 			return -ENOMEM;
188 	}
189 
190 	ret = vfs_parse_fs_param(fc, &param);
191 	kfree(param.string);
192 	return ret;
193 }
194 EXPORT_SYMBOL(vfs_parse_fs_string);
195 
196 /**
197  * generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
198  * @ctx: The superblock configuration to fill in.
199  * @data: The data to parse
200  *
201  * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
202  * called from the ->monolithic_mount_data() fs_context operation.
203  *
204  * Returns 0 on success or the error returned by the ->parse_option() fs_context
205  * operation on failure.
206  */
207 int generic_parse_monolithic(struct fs_context *fc, void *data)
208 {
209 	char *options = data, *key;
210 	int ret = 0;
211 
212 	if (!options)
213 		return 0;
214 
215 	ret = security_sb_eat_lsm_opts(options, &fc->security);
216 	if (ret)
217 		return ret;
218 
219 	while ((key = strsep(&options, ",")) != NULL) {
220 		if (*key) {
221 			size_t v_len = 0;
222 			char *value = strchr(key, '=');
223 
224 			if (value) {
225 				if (value == key)
226 					continue;
227 				*value++ = 0;
228 				v_len = strlen(value);
229 			}
230 			ret = vfs_parse_fs_string(fc, key, value, v_len);
231 			if (ret < 0)
232 				break;
233 		}
234 	}
235 
236 	return ret;
237 }
238 EXPORT_SYMBOL(generic_parse_monolithic);
239 
240 /**
241  * alloc_fs_context - Create a filesystem context.
242  * @fs_type: The filesystem type.
243  * @reference: The dentry from which this one derives (or NULL)
244  * @sb_flags: Filesystem/superblock flags (SB_*)
245  * @sb_flags_mask: Applicable members of @sb_flags
246  * @purpose: The purpose that this configuration shall be used for.
247  *
248  * Open a filesystem and create a mount context.  The mount context is
249  * initialised with the supplied flags and, if a submount/automount from
250  * another superblock (referred to by @reference) is supplied, may have
251  * parameters such as namespaces copied across from that superblock.
252  */
253 static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
254 				      struct dentry *reference,
255 				      unsigned int sb_flags,
256 				      unsigned int sb_flags_mask,
257 				      enum fs_context_purpose purpose)
258 {
259 	int (*init_fs_context)(struct fs_context *);
260 	struct fs_context *fc;
261 	int ret = -ENOMEM;
262 
263 	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
264 	if (!fc)
265 		return ERR_PTR(-ENOMEM);
266 
267 	fc->purpose	= purpose;
268 	fc->sb_flags	= sb_flags;
269 	fc->sb_flags_mask = sb_flags_mask;
270 	fc->fs_type	= get_filesystem(fs_type);
271 	fc->cred	= get_current_cred();
272 	fc->net_ns	= get_net(current->nsproxy->net_ns);
273 
274 	switch (purpose) {
275 	case FS_CONTEXT_FOR_MOUNT:
276 		fc->user_ns = get_user_ns(fc->cred->user_ns);
277 		break;
278 	case FS_CONTEXT_FOR_SUBMOUNT:
279 		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
280 		break;
281 	case FS_CONTEXT_FOR_RECONFIGURE:
282 		/* We don't pin any namespaces as the superblock's
283 		 * subscriptions cannot be changed at this point.
284 		 */
285 		atomic_inc(&reference->d_sb->s_active);
286 		fc->root = dget(reference);
287 		break;
288 	}
289 
290 	/* TODO: Make all filesystems support this unconditionally */
291 	init_fs_context = fc->fs_type->init_fs_context;
292 	if (!init_fs_context)
293 		init_fs_context = legacy_init_fs_context;
294 
295 	ret = init_fs_context(fc);
296 	if (ret < 0)
297 		goto err_fc;
298 	fc->need_free = true;
299 	return fc;
300 
301 err_fc:
302 	put_fs_context(fc);
303 	return ERR_PTR(ret);
304 }
305 
306 struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
307 					unsigned int sb_flags)
308 {
309 	return alloc_fs_context(fs_type, NULL, sb_flags, 0,
310 					FS_CONTEXT_FOR_MOUNT);
311 }
312 EXPORT_SYMBOL(fs_context_for_mount);
313 
314 struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
315 					unsigned int sb_flags,
316 					unsigned int sb_flags_mask)
317 {
318 	return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
319 				sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
320 }
321 EXPORT_SYMBOL(fs_context_for_reconfigure);
322 
323 struct fs_context *fs_context_for_submount(struct file_system_type *type,
324 					   struct dentry *reference)
325 {
326 	return alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
327 }
328 EXPORT_SYMBOL(fs_context_for_submount);
329 
330 void fc_drop_locked(struct fs_context *fc)
331 {
332 	struct super_block *sb = fc->root->d_sb;
333 	dput(fc->root);
334 	fc->root = NULL;
335 	deactivate_locked_super(sb);
336 }
337 
338 static void legacy_fs_context_free(struct fs_context *fc);
339 
340 /**
341  * vfs_dup_fc_config: Duplicate a filesystem context.
342  * @src_fc: The context to copy.
343  */
344 struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
345 {
346 	struct fs_context *fc;
347 	int ret;
348 
349 	if (!src_fc->ops->dup)
350 		return ERR_PTR(-EOPNOTSUPP);
351 
352 	fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
353 	if (!fc)
354 		return ERR_PTR(-ENOMEM);
355 
356 	fc->fs_private	= NULL;
357 	fc->s_fs_info	= NULL;
358 	fc->source	= NULL;
359 	fc->security	= NULL;
360 	get_filesystem(fc->fs_type);
361 	get_net(fc->net_ns);
362 	get_user_ns(fc->user_ns);
363 	get_cred(fc->cred);
364 
365 	/* Can't call put until we've called ->dup */
366 	ret = fc->ops->dup(fc, src_fc);
367 	if (ret < 0)
368 		goto err_fc;
369 
370 	ret = security_fs_context_dup(fc, src_fc);
371 	if (ret < 0)
372 		goto err_fc;
373 	return fc;
374 
375 err_fc:
376 	put_fs_context(fc);
377 	return ERR_PTR(ret);
378 }
379 EXPORT_SYMBOL(vfs_dup_fs_context);
380 
381 #ifdef CONFIG_PRINTK
382 /**
383  * logfc - Log a message to a filesystem context
384  * @fc: The filesystem context to log to.
385  * @fmt: The format of the buffer.
386  */
387 void logfc(struct fs_context *fc, const char *fmt, ...)
388 {
389 	va_list va;
390 
391 	va_start(va, fmt);
392 
393 	switch (fmt[0]) {
394 	case 'w':
395 		vprintk_emit(0, LOGLEVEL_WARNING, NULL, 0, fmt, va);
396 		break;
397 	case 'e':
398 		vprintk_emit(0, LOGLEVEL_ERR, NULL, 0, fmt, va);
399 		break;
400 	default:
401 		vprintk_emit(0, LOGLEVEL_NOTICE, NULL, 0, fmt, va);
402 		break;
403 	}
404 
405 	pr_cont("\n");
406 	va_end(va);
407 }
408 EXPORT_SYMBOL(logfc);
409 #endif
410 
411 /**
412  * put_fs_context - Dispose of a superblock configuration context.
413  * @fc: The context to dispose of.
414  */
415 void put_fs_context(struct fs_context *fc)
416 {
417 	struct super_block *sb;
418 
419 	if (fc->root) {
420 		sb = fc->root->d_sb;
421 		dput(fc->root);
422 		fc->root = NULL;
423 		deactivate_super(sb);
424 	}
425 
426 	if (fc->need_free && fc->ops && fc->ops->free)
427 		fc->ops->free(fc);
428 
429 	security_free_mnt_opts(&fc->security);
430 	put_net(fc->net_ns);
431 	put_user_ns(fc->user_ns);
432 	put_cred(fc->cred);
433 	kfree(fc->subtype);
434 	put_filesystem(fc->fs_type);
435 	kfree(fc->source);
436 	kfree(fc);
437 }
438 EXPORT_SYMBOL(put_fs_context);
439 
440 /*
441  * Free the config for a filesystem that doesn't support fs_context.
442  */
443 static void legacy_fs_context_free(struct fs_context *fc)
444 {
445 	struct legacy_fs_context *ctx = fc->fs_private;
446 
447 	if (ctx) {
448 		if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
449 			kfree(ctx->legacy_data);
450 		kfree(ctx);
451 	}
452 }
453 
454 /*
455  * Duplicate a legacy config.
456  */
457 static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
458 {
459 	struct legacy_fs_context *ctx;
460 	struct legacy_fs_context *src_ctx = src_fc->fs_private;
461 
462 	ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
463 	if (!ctx)
464 		return -ENOMEM;
465 
466 	if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
467 		ctx->legacy_data = kmemdup(src_ctx->legacy_data,
468 					   src_ctx->data_size, GFP_KERNEL);
469 		if (!ctx->legacy_data) {
470 			kfree(ctx);
471 			return -ENOMEM;
472 		}
473 	}
474 
475 	fc->fs_private = ctx;
476 	return 0;
477 }
478 
479 /*
480  * Add a parameter to a legacy config.  We build up a comma-separated list of
481  * options.
482  */
483 static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
484 {
485 	struct legacy_fs_context *ctx = fc->fs_private;
486 	unsigned int size = ctx->data_size;
487 	size_t len = 0;
488 
489 	if (strcmp(param->key, "source") == 0) {
490 		if (param->type != fs_value_is_string)
491 			return invalf(fc, "VFS: Legacy: Non-string source");
492 		if (fc->source)
493 			return invalf(fc, "VFS: Legacy: Multiple sources");
494 		fc->source = param->string;
495 		param->string = NULL;
496 		return 0;
497 	}
498 
499 	if ((fc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
500 	    strcmp(param->key, "subtype") == 0) {
501 		if (param->type != fs_value_is_string)
502 			return invalf(fc, "VFS: Legacy: Non-string subtype");
503 		if (fc->subtype)
504 			return invalf(fc, "VFS: Legacy: Multiple subtype");
505 		fc->subtype = param->string;
506 		param->string = NULL;
507 		return 0;
508 	}
509 
510 	if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
511 		return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
512 
513 	switch (param->type) {
514 	case fs_value_is_string:
515 		len = 1 + param->size;
516 		/* Fall through */
517 	case fs_value_is_flag:
518 		len += strlen(param->key);
519 		break;
520 	default:
521 		return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
522 			      param->key);
523 	}
524 
525 	if (len > PAGE_SIZE - 2 - size)
526 		return invalf(fc, "VFS: Legacy: Cumulative options too large");
527 	if (strchr(param->key, ',') ||
528 	    (param->type == fs_value_is_string &&
529 	     memchr(param->string, ',', param->size)))
530 		return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
531 			      param->key);
532 	if (!ctx->legacy_data) {
533 		ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
534 		if (!ctx->legacy_data)
535 			return -ENOMEM;
536 	}
537 
538 	ctx->legacy_data[size++] = ',';
539 	len = strlen(param->key);
540 	memcpy(ctx->legacy_data + size, param->key, len);
541 	size += len;
542 	if (param->type == fs_value_is_string) {
543 		ctx->legacy_data[size++] = '=';
544 		memcpy(ctx->legacy_data + size, param->string, param->size);
545 		size += param->size;
546 	}
547 	ctx->legacy_data[size] = '\0';
548 	ctx->data_size = size;
549 	ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
550 	return 0;
551 }
552 
553 /*
554  * Add monolithic mount data.
555  */
556 static int legacy_parse_monolithic(struct fs_context *fc, void *data)
557 {
558 	struct legacy_fs_context *ctx = fc->fs_private;
559 
560 	if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
561 		pr_warn("VFS: Can't mix monolithic and individual options\n");
562 		return -EINVAL;
563 	}
564 
565 	ctx->legacy_data = data;
566 	ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
567 	if (!ctx->legacy_data)
568 		return 0;
569 
570 	if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
571 		return 0;
572 	return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
573 }
574 
575 /*
576  * Get a mountable root with the legacy mount command.
577  */
578 static int legacy_get_tree(struct fs_context *fc)
579 {
580 	struct legacy_fs_context *ctx = fc->fs_private;
581 	struct super_block *sb;
582 	struct dentry *root;
583 
584 	root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
585 				      fc->source, ctx->legacy_data);
586 	if (IS_ERR(root))
587 		return PTR_ERR(root);
588 
589 	sb = root->d_sb;
590 	BUG_ON(!sb);
591 
592 	fc->root = root;
593 	return 0;
594 }
595 
596 /*
597  * Handle remount.
598  */
599 static int legacy_reconfigure(struct fs_context *fc)
600 {
601 	struct legacy_fs_context *ctx = fc->fs_private;
602 	struct super_block *sb = fc->root->d_sb;
603 
604 	if (!sb->s_op->remount_fs)
605 		return 0;
606 
607 	return sb->s_op->remount_fs(sb, &fc->sb_flags,
608 				    ctx ? ctx->legacy_data : NULL);
609 }
610 
611 const struct fs_context_operations legacy_fs_context_ops = {
612 	.free			= legacy_fs_context_free,
613 	.dup			= legacy_fs_context_dup,
614 	.parse_param		= legacy_parse_param,
615 	.parse_monolithic	= legacy_parse_monolithic,
616 	.get_tree		= legacy_get_tree,
617 	.reconfigure		= legacy_reconfigure,
618 };
619 
620 /*
621  * Initialise a legacy context for a filesystem that doesn't support
622  * fs_context.
623  */
624 static int legacy_init_fs_context(struct fs_context *fc)
625 {
626 	fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL);
627 	if (!fc->fs_private)
628 		return -ENOMEM;
629 	fc->ops = &legacy_fs_context_ops;
630 	return 0;
631 }
632 
633 int parse_monolithic_mount_data(struct fs_context *fc, void *data)
634 {
635 	int (*monolithic_mount_data)(struct fs_context *, void *);
636 
637 	monolithic_mount_data = fc->ops->parse_monolithic;
638 	if (!monolithic_mount_data)
639 		monolithic_mount_data = generic_parse_monolithic;
640 
641 	return monolithic_mount_data(fc, data);
642 }
643