xref: /linux/fs/fs_context.c (revision 0ea5c948cb64bab5bc7a5516774eb8536f05aa0d)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Provide a way to create a superblock configuration context within the kernel
3  * that allows a superblock to be set up prior to mounting.
4  *
5  * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
6  * Written by David Howells (dhowells@redhat.com)
7  */
8 
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10 #include <linux/module.h>
11 #include <linux/fs_context.h>
12 #include <linux/fs_parser.h>
13 #include <linux/fs.h>
14 #include <linux/mount.h>
15 #include <linux/nsproxy.h>
16 #include <linux/slab.h>
17 #include <linux/magic.h>
18 #include <linux/security.h>
19 #include <linux/mnt_namespace.h>
20 #include <linux/pid_namespace.h>
21 #include <linux/user_namespace.h>
22 #include <net/net_namespace.h>
23 #include <asm/sections.h>
24 #include "mount.h"
25 #include "internal.h"
26 
27 enum legacy_fs_param {
28 	LEGACY_FS_UNSET_PARAMS,
29 	LEGACY_FS_MONOLITHIC_PARAMS,
30 	LEGACY_FS_INDIVIDUAL_PARAMS,
31 };
32 
33 struct legacy_fs_context {
34 	char			*legacy_data;	/* Data page for legacy filesystems */
35 	size_t			data_size;
36 	enum legacy_fs_param	param_type;
37 };
38 
39 static int legacy_init_fs_context(struct fs_context *fc);
40 
41 static const struct constant_table common_set_sb_flag[] = {
42 	{ "dirsync",	SB_DIRSYNC },
43 	{ "lazytime",	SB_LAZYTIME },
44 	{ "mand",	SB_MANDLOCK },
45 	{ "ro",		SB_RDONLY },
46 	{ "sync",	SB_SYNCHRONOUS },
47 	{ },
48 };
49 
50 static const struct constant_table common_clear_sb_flag[] = {
51 	{ "async",	SB_SYNCHRONOUS },
52 	{ "nolazytime",	SB_LAZYTIME },
53 	{ "nomand",	SB_MANDLOCK },
54 	{ "rw",		SB_RDONLY },
55 	{ },
56 };
57 
58 /*
59  * Check for a common mount option that manipulates s_flags.
60  */
vfs_parse_sb_flag(struct fs_context * fc,const char * key)61 static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
62 {
63 	unsigned int token;
64 
65 	token = lookup_constant(common_set_sb_flag, key, 0);
66 	if (token) {
67 		fc->sb_flags |= token;
68 		fc->sb_flags_mask |= token;
69 		return 0;
70 	}
71 
72 	token = lookup_constant(common_clear_sb_flag, key, 0);
73 	if (token) {
74 		fc->sb_flags &= ~token;
75 		fc->sb_flags_mask |= token;
76 		return 0;
77 	}
78 
79 	return -ENOPARAM;
80 }
81 
82 /**
83  * vfs_parse_fs_param_source - Handle setting "source" via parameter
84  * @fc: The filesystem context to modify
85  * @param: The parameter
86  *
87  * This is a simple helper for filesystems to verify that the "source" they
88  * accept is sane.
89  *
90  * Returns 0 on success, -ENOPARAM if this is not  "source" parameter, and
91  * -EINVAL otherwise. In the event of failure, supplementary error information
92  *  is logged.
93  */
vfs_parse_fs_param_source(struct fs_context * fc,struct fs_parameter * param)94 int vfs_parse_fs_param_source(struct fs_context *fc, struct fs_parameter *param)
95 {
96 	if (strcmp(param->key, "source") != 0)
97 		return -ENOPARAM;
98 
99 	if (param->type != fs_value_is_string)
100 		return invalf(fc, "Non-string source");
101 
102 	if (fc->source)
103 		return invalf(fc, "Multiple sources");
104 
105 	fc->source = param->string;
106 	param->string = NULL;
107 	return 0;
108 }
109 EXPORT_SYMBOL(vfs_parse_fs_param_source);
110 
111 /**
112  * vfs_parse_fs_param - Add a single parameter to a superblock config
113  * @fc: The filesystem context to modify
114  * @param: The parameter
115  *
116  * A single mount option in string form is applied to the filesystem context
117  * being set up.  Certain standard options (for example "ro") are translated
118  * into flag bits without going to the filesystem.  The active security module
119  * is allowed to observe and poach options.  Any other options are passed over
120  * to the filesystem to parse.
121  *
122  * This may be called multiple times for a context.
123  *
124  * Returns 0 on success and a negative error code on failure.  In the event of
125  * failure, supplementary error information may have been set.
126  */
vfs_parse_fs_param(struct fs_context * fc,struct fs_parameter * param)127 int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
128 {
129 	int ret;
130 
131 	if (!param->key)
132 		return invalf(fc, "Unnamed parameter\n");
133 
134 	ret = vfs_parse_sb_flag(fc, param->key);
135 	if (ret != -ENOPARAM)
136 		return ret;
137 
138 	ret = security_fs_context_parse_param(fc, param);
139 	if (ret != -ENOPARAM)
140 		/* Param belongs to the LSM or is disallowed by the LSM; so
141 		 * don't pass to the FS.
142 		 */
143 		return ret;
144 
145 	if (fc->ops->parse_param) {
146 		ret = fc->ops->parse_param(fc, param);
147 		if (ret != -ENOPARAM)
148 			return ret;
149 	}
150 
151 	/* If the filesystem doesn't take any arguments, give it the
152 	 * default handling of source.
153 	 */
154 	ret = vfs_parse_fs_param_source(fc, param);
155 	if (ret != -ENOPARAM)
156 		return ret;
157 
158 	return invalf(fc, "%s: Unknown parameter '%s'",
159 		      fc->fs_type->name, param->key);
160 }
161 EXPORT_SYMBOL(vfs_parse_fs_param);
162 
163 /**
164  * vfs_parse_fs_string - Convenience function to just parse a string.
165  * @fc: Filesystem context.
166  * @key: Parameter name.
167  * @value: Default value.
168  * @v_size: Maximum number of bytes in the value.
169  */
vfs_parse_fs_string(struct fs_context * fc,const char * key,const char * value,size_t v_size)170 int vfs_parse_fs_string(struct fs_context *fc, const char *key,
171 			const char *value, size_t v_size)
172 {
173 	int ret;
174 
175 	struct fs_parameter param = {
176 		.key	= key,
177 		.type	= fs_value_is_flag,
178 		.size	= v_size,
179 	};
180 
181 	if (value) {
182 		param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
183 		if (!param.string)
184 			return -ENOMEM;
185 		param.type = fs_value_is_string;
186 	}
187 
188 	ret = vfs_parse_fs_param(fc, &param);
189 	kfree(param.string);
190 	return ret;
191 }
192 EXPORT_SYMBOL(vfs_parse_fs_string);
193 
194 /**
195  * vfs_parse_monolithic_sep - Parse key[=val][,key[=val]]* mount data
196  * @fc: The superblock configuration to fill in.
197  * @data: The data to parse
198  * @sep: callback for separating next option
199  *
200  * Parse a blob of data that's in key[=val][,key[=val]]* form with a custom
201  * option separator callback.
202  *
203  * Returns 0 on success or the error returned by the ->parse_option() fs_context
204  * operation on failure.
205  */
vfs_parse_monolithic_sep(struct fs_context * fc,void * data,char * (* sep)(char **))206 int vfs_parse_monolithic_sep(struct fs_context *fc, void *data,
207 			     char *(*sep)(char **))
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 = sep(&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(vfs_parse_monolithic_sep);
239 
vfs_parse_comma_sep(char ** s)240 static char *vfs_parse_comma_sep(char **s)
241 {
242 	return strsep(s, ",");
243 }
244 
245 /**
246  * generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
247  * @fc: The superblock configuration to fill in.
248  * @data: The data to parse
249  *
250  * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
251  * called from the ->monolithic_mount_data() fs_context operation.
252  *
253  * Returns 0 on success or the error returned by the ->parse_option() fs_context
254  * operation on failure.
255  */
generic_parse_monolithic(struct fs_context * fc,void * data)256 int generic_parse_monolithic(struct fs_context *fc, void *data)
257 {
258 	return vfs_parse_monolithic_sep(fc, data, vfs_parse_comma_sep);
259 }
260 EXPORT_SYMBOL(generic_parse_monolithic);
261 
262 /**
263  * alloc_fs_context - Create a filesystem context.
264  * @fs_type: The filesystem type.
265  * @reference: The dentry from which this one derives (or NULL)
266  * @sb_flags: Filesystem/superblock flags (SB_*)
267  * @sb_flags_mask: Applicable members of @sb_flags
268  * @purpose: The purpose that this configuration shall be used for.
269  *
270  * Open a filesystem and create a mount context.  The mount context is
271  * initialised with the supplied flags and, if a submount/automount from
272  * another superblock (referred to by @reference) is supplied, may have
273  * parameters such as namespaces copied across from that superblock.
274  */
alloc_fs_context(struct file_system_type * fs_type,struct dentry * reference,unsigned int sb_flags,unsigned int sb_flags_mask,enum fs_context_purpose purpose)275 static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
276 				      struct dentry *reference,
277 				      unsigned int sb_flags,
278 				      unsigned int sb_flags_mask,
279 				      enum fs_context_purpose purpose)
280 {
281 	int (*init_fs_context)(struct fs_context *);
282 	struct fs_context *fc;
283 	int ret = -ENOMEM;
284 
285 	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL_ACCOUNT);
286 	if (!fc)
287 		return ERR_PTR(-ENOMEM);
288 
289 	fc->purpose	= purpose;
290 	fc->sb_flags	= sb_flags;
291 	fc->sb_flags_mask = sb_flags_mask;
292 	fc->fs_type	= get_filesystem(fs_type);
293 	fc->cred	= get_current_cred();
294 	fc->net_ns	= get_net(current->nsproxy->net_ns);
295 	fc->log.prefix	= fs_type->name;
296 
297 	mutex_init(&fc->uapi_mutex);
298 
299 	switch (purpose) {
300 	case FS_CONTEXT_FOR_MOUNT:
301 		fc->user_ns = get_user_ns(fc->cred->user_ns);
302 		break;
303 	case FS_CONTEXT_FOR_SUBMOUNT:
304 		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
305 		break;
306 	case FS_CONTEXT_FOR_RECONFIGURE:
307 		atomic_inc(&reference->d_sb->s_active);
308 		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
309 		fc->root = dget(reference);
310 		break;
311 	}
312 
313 	/* TODO: Make all filesystems support this unconditionally */
314 	init_fs_context = fc->fs_type->init_fs_context;
315 	if (!init_fs_context)
316 		init_fs_context = legacy_init_fs_context;
317 
318 	ret = init_fs_context(fc);
319 	if (ret < 0)
320 		goto err_fc;
321 	fc->need_free = true;
322 	return fc;
323 
324 err_fc:
325 	put_fs_context(fc);
326 	return ERR_PTR(ret);
327 }
328 
fs_context_for_mount(struct file_system_type * fs_type,unsigned int sb_flags)329 struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
330 					unsigned int sb_flags)
331 {
332 	return alloc_fs_context(fs_type, NULL, sb_flags, 0,
333 					FS_CONTEXT_FOR_MOUNT);
334 }
335 EXPORT_SYMBOL(fs_context_for_mount);
336 
fs_context_for_reconfigure(struct dentry * dentry,unsigned int sb_flags,unsigned int sb_flags_mask)337 struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
338 					unsigned int sb_flags,
339 					unsigned int sb_flags_mask)
340 {
341 	return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
342 				sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
343 }
344 EXPORT_SYMBOL(fs_context_for_reconfigure);
345 
346 /**
347  * fs_context_for_submount: allocate a new fs_context for a submount
348  * @type: file_system_type of the new context
349  * @reference: reference dentry from which to copy relevant info
350  *
351  * Allocate a new fs_context suitable for a submount. This also ensures that
352  * the fc->security object is inherited from @reference (if needed).
353  */
fs_context_for_submount(struct file_system_type * type,struct dentry * reference)354 struct fs_context *fs_context_for_submount(struct file_system_type *type,
355 					   struct dentry *reference)
356 {
357 	struct fs_context *fc;
358 	int ret;
359 
360 	fc = alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
361 	if (IS_ERR(fc))
362 		return fc;
363 
364 	ret = security_fs_context_submount(fc, reference->d_sb);
365 	if (ret) {
366 		put_fs_context(fc);
367 		return ERR_PTR(ret);
368 	}
369 
370 	return fc;
371 }
372 EXPORT_SYMBOL(fs_context_for_submount);
373 
fc_drop_locked(struct fs_context * fc)374 void fc_drop_locked(struct fs_context *fc)
375 {
376 	struct super_block *sb = fc->root->d_sb;
377 	dput(fc->root);
378 	fc->root = NULL;
379 	deactivate_locked_super(sb);
380 }
381 
382 static void legacy_fs_context_free(struct fs_context *fc);
383 
384 /**
385  * vfs_dup_fs_context - Duplicate a filesystem context.
386  * @src_fc: The context to copy.
387  */
vfs_dup_fs_context(struct fs_context * src_fc)388 struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
389 {
390 	struct fs_context *fc;
391 	int ret;
392 
393 	if (!src_fc->ops->dup)
394 		return ERR_PTR(-EOPNOTSUPP);
395 
396 	fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
397 	if (!fc)
398 		return ERR_PTR(-ENOMEM);
399 
400 	mutex_init(&fc->uapi_mutex);
401 
402 	fc->fs_private	= NULL;
403 	fc->s_fs_info	= NULL;
404 	fc->source	= NULL;
405 	fc->security	= NULL;
406 	get_filesystem(fc->fs_type);
407 	get_net(fc->net_ns);
408 	get_user_ns(fc->user_ns);
409 	get_cred(fc->cred);
410 	if (fc->log.log)
411 		refcount_inc(&fc->log.log->usage);
412 
413 	/* Can't call put until we've called ->dup */
414 	ret = fc->ops->dup(fc, src_fc);
415 	if (ret < 0)
416 		goto err_fc;
417 
418 	ret = security_fs_context_dup(fc, src_fc);
419 	if (ret < 0)
420 		goto err_fc;
421 	return fc;
422 
423 err_fc:
424 	put_fs_context(fc);
425 	return ERR_PTR(ret);
426 }
427 EXPORT_SYMBOL(vfs_dup_fs_context);
428 
429 /**
430  * logfc - Log a message to a filesystem context
431  * @log: The filesystem context to log to, or NULL to use printk.
432  * @prefix: A string to prefix the output with, or NULL.
433  * @level: 'w' for a warning, 'e' for an error.  Anything else is a notice.
434  * @fmt: The format of the buffer.
435  */
logfc(struct fc_log * log,const char * prefix,char level,const char * fmt,...)436 void logfc(struct fc_log *log, const char *prefix, char level, const char *fmt, ...)
437 {
438 	va_list va;
439 	struct va_format vaf = {.fmt = fmt, .va = &va};
440 
441 	va_start(va, fmt);
442 	if (!log) {
443 		switch (level) {
444 		case 'w':
445 			printk(KERN_WARNING "%s%s%pV\n", prefix ? prefix : "",
446 						prefix ? ": " : "", &vaf);
447 			break;
448 		case 'e':
449 			printk(KERN_ERR "%s%s%pV\n", prefix ? prefix : "",
450 						prefix ? ": " : "", &vaf);
451 			break;
452 		default:
453 			printk(KERN_NOTICE "%s%s%pV\n", prefix ? prefix : "",
454 						prefix ? ": " : "", &vaf);
455 			break;
456 		}
457 	} else {
458 		unsigned int logsize = ARRAY_SIZE(log->buffer);
459 		u8 index;
460 		char *q = kasprintf(GFP_KERNEL, "%c %s%s%pV\n", level,
461 						prefix ? prefix : "",
462 						prefix ? ": " : "", &vaf);
463 
464 		index = log->head & (logsize - 1);
465 		BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
466 			     sizeof(log->tail) != sizeof(u8));
467 		if ((u8)(log->head - log->tail) == logsize) {
468 			/* The buffer is full, discard the oldest message */
469 			if (log->need_free & (1 << index))
470 				kfree(log->buffer[index]);
471 			log->tail++;
472 		}
473 
474 		log->buffer[index] = q ? q : "OOM: Can't store error string";
475 		if (q)
476 			log->need_free |= 1 << index;
477 		else
478 			log->need_free &= ~(1 << index);
479 		log->head++;
480 	}
481 	va_end(va);
482 }
483 EXPORT_SYMBOL(logfc);
484 
485 /*
486  * Free a logging structure.
487  */
put_fc_log(struct fs_context * fc)488 static void put_fc_log(struct fs_context *fc)
489 {
490 	struct fc_log *log = fc->log.log;
491 	int i;
492 
493 	if (log) {
494 		if (refcount_dec_and_test(&log->usage)) {
495 			fc->log.log = NULL;
496 			for (i = 0; i <= 7; i++)
497 				if (log->need_free & (1 << i))
498 					kfree(log->buffer[i]);
499 			kfree(log);
500 		}
501 	}
502 }
503 
504 /**
505  * put_fs_context - Dispose of a superblock configuration context.
506  * @fc: The context to dispose of.
507  */
put_fs_context(struct fs_context * fc)508 void put_fs_context(struct fs_context *fc)
509 {
510 	struct super_block *sb;
511 
512 	if (fc->root) {
513 		sb = fc->root->d_sb;
514 		dput(fc->root);
515 		fc->root = NULL;
516 		deactivate_super(sb);
517 	}
518 
519 	if (fc->need_free && fc->ops && fc->ops->free)
520 		fc->ops->free(fc);
521 
522 	security_free_mnt_opts(&fc->security);
523 	put_net(fc->net_ns);
524 	put_user_ns(fc->user_ns);
525 	put_cred(fc->cred);
526 	put_fc_log(fc);
527 	put_filesystem(fc->fs_type);
528 	kfree(fc->source);
529 	kfree(fc);
530 }
531 EXPORT_SYMBOL(put_fs_context);
532 
533 /*
534  * Free the config for a filesystem that doesn't support fs_context.
535  */
legacy_fs_context_free(struct fs_context * fc)536 static void legacy_fs_context_free(struct fs_context *fc)
537 {
538 	struct legacy_fs_context *ctx = fc->fs_private;
539 
540 	if (ctx) {
541 		if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
542 			kfree(ctx->legacy_data);
543 		kfree(ctx);
544 	}
545 }
546 
547 /*
548  * Duplicate a legacy config.
549  */
legacy_fs_context_dup(struct fs_context * fc,struct fs_context * src_fc)550 static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
551 {
552 	struct legacy_fs_context *ctx;
553 	struct legacy_fs_context *src_ctx = src_fc->fs_private;
554 
555 	ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
556 	if (!ctx)
557 		return -ENOMEM;
558 
559 	if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
560 		ctx->legacy_data = kmemdup(src_ctx->legacy_data,
561 					   src_ctx->data_size, GFP_KERNEL);
562 		if (!ctx->legacy_data) {
563 			kfree(ctx);
564 			return -ENOMEM;
565 		}
566 	}
567 
568 	fc->fs_private = ctx;
569 	return 0;
570 }
571 
572 /*
573  * Add a parameter to a legacy config.  We build up a comma-separated list of
574  * options.
575  */
legacy_parse_param(struct fs_context * fc,struct fs_parameter * param)576 static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
577 {
578 	struct legacy_fs_context *ctx = fc->fs_private;
579 	unsigned int size = ctx->data_size;
580 	size_t len = 0;
581 	int ret;
582 
583 	ret = vfs_parse_fs_param_source(fc, param);
584 	if (ret != -ENOPARAM)
585 		return ret;
586 
587 	if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
588 		return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
589 
590 	switch (param->type) {
591 	case fs_value_is_string:
592 		len = 1 + param->size;
593 		fallthrough;
594 	case fs_value_is_flag:
595 		len += strlen(param->key);
596 		break;
597 	default:
598 		return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
599 			      param->key);
600 	}
601 
602 	if (size + len + 2 > PAGE_SIZE)
603 		return invalf(fc, "VFS: Legacy: Cumulative options too large");
604 	if (strchr(param->key, ',') ||
605 	    (param->type == fs_value_is_string &&
606 	     memchr(param->string, ',', param->size)))
607 		return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
608 			      param->key);
609 	if (!ctx->legacy_data) {
610 		ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
611 		if (!ctx->legacy_data)
612 			return -ENOMEM;
613 	}
614 
615 	if (size)
616 		ctx->legacy_data[size++] = ',';
617 	len = strlen(param->key);
618 	memcpy(ctx->legacy_data + size, param->key, len);
619 	size += len;
620 	if (param->type == fs_value_is_string) {
621 		ctx->legacy_data[size++] = '=';
622 		memcpy(ctx->legacy_data + size, param->string, param->size);
623 		size += param->size;
624 	}
625 	ctx->legacy_data[size] = '\0';
626 	ctx->data_size = size;
627 	ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
628 	return 0;
629 }
630 
631 /*
632  * Add monolithic mount data.
633  */
legacy_parse_monolithic(struct fs_context * fc,void * data)634 static int legacy_parse_monolithic(struct fs_context *fc, void *data)
635 {
636 	struct legacy_fs_context *ctx = fc->fs_private;
637 
638 	if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
639 		pr_warn("VFS: Can't mix monolithic and individual options\n");
640 		return -EINVAL;
641 	}
642 
643 	ctx->legacy_data = data;
644 	ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
645 	if (!ctx->legacy_data)
646 		return 0;
647 
648 	if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
649 		return 0;
650 	return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
651 }
652 
653 /*
654  * Get a mountable root with the legacy mount command.
655  */
legacy_get_tree(struct fs_context * fc)656 static int legacy_get_tree(struct fs_context *fc)
657 {
658 	struct legacy_fs_context *ctx = fc->fs_private;
659 	struct super_block *sb;
660 	struct dentry *root;
661 
662 	root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
663 				      fc->source, ctx->legacy_data);
664 	if (IS_ERR(root))
665 		return PTR_ERR(root);
666 
667 	sb = root->d_sb;
668 	BUG_ON(!sb);
669 
670 	fc->root = root;
671 	return 0;
672 }
673 
674 /*
675  * Handle remount.
676  */
legacy_reconfigure(struct fs_context * fc)677 static int legacy_reconfigure(struct fs_context *fc)
678 {
679 	struct legacy_fs_context *ctx = fc->fs_private;
680 	struct super_block *sb = fc->root->d_sb;
681 
682 	if (!sb->s_op->remount_fs)
683 		return 0;
684 
685 	return sb->s_op->remount_fs(sb, &fc->sb_flags,
686 				    ctx ? ctx->legacy_data : NULL);
687 }
688 
689 const struct fs_context_operations legacy_fs_context_ops = {
690 	.free			= legacy_fs_context_free,
691 	.dup			= legacy_fs_context_dup,
692 	.parse_param		= legacy_parse_param,
693 	.parse_monolithic	= legacy_parse_monolithic,
694 	.get_tree		= legacy_get_tree,
695 	.reconfigure		= legacy_reconfigure,
696 };
697 
698 /*
699  * Initialise a legacy context for a filesystem that doesn't support
700  * fs_context.
701  */
legacy_init_fs_context(struct fs_context * fc)702 static int legacy_init_fs_context(struct fs_context *fc)
703 {
704 	fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL_ACCOUNT);
705 	if (!fc->fs_private)
706 		return -ENOMEM;
707 	fc->ops = &legacy_fs_context_ops;
708 	return 0;
709 }
710 
parse_monolithic_mount_data(struct fs_context * fc,void * data)711 int parse_monolithic_mount_data(struct fs_context *fc, void *data)
712 {
713 	int (*monolithic_mount_data)(struct fs_context *, void *);
714 
715 	monolithic_mount_data = fc->ops->parse_monolithic;
716 	if (!monolithic_mount_data)
717 		monolithic_mount_data = generic_parse_monolithic;
718 
719 	return monolithic_mount_data(fc, data);
720 }
721 
722 /*
723  * Clean up a context after performing an action on it and put it into a state
724  * from where it can be used to reconfigure a superblock.
725  *
726  * Note that here we do only the parts that can't fail; the rest is in
727  * finish_clean_context() below and in between those fs_context is marked
728  * FS_CONTEXT_AWAITING_RECONF.  The reason for splitup is that after
729  * successful mount or remount we need to report success to userland.
730  * Trying to do full reinit (for the sake of possible subsequent remount)
731  * and failing to allocate memory would've put us into a nasty situation.
732  * So here we only discard the old state and reinitialization is left
733  * until we actually try to reconfigure.
734  */
vfs_clean_context(struct fs_context * fc)735 void vfs_clean_context(struct fs_context *fc)
736 {
737 	if (fc->need_free && fc->ops && fc->ops->free)
738 		fc->ops->free(fc);
739 	fc->need_free = false;
740 	fc->fs_private = NULL;
741 	fc->s_fs_info = NULL;
742 	fc->sb_flags = 0;
743 	security_free_mnt_opts(&fc->security);
744 	kfree(fc->source);
745 	fc->source = NULL;
746 	fc->exclusive = false;
747 
748 	fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
749 	fc->phase = FS_CONTEXT_AWAITING_RECONF;
750 }
751 
finish_clean_context(struct fs_context * fc)752 int finish_clean_context(struct fs_context *fc)
753 {
754 	int error;
755 
756 	if (fc->phase != FS_CONTEXT_AWAITING_RECONF)
757 		return 0;
758 
759 	if (fc->fs_type->init_fs_context)
760 		error = fc->fs_type->init_fs_context(fc);
761 	else
762 		error = legacy_init_fs_context(fc);
763 	if (unlikely(error)) {
764 		fc->phase = FS_CONTEXT_FAILED;
765 		return error;
766 	}
767 	fc->need_free = true;
768 	fc->phase = FS_CONTEXT_RECONF_PARAMS;
769 	return 0;
770 }
771