fs_context.c

  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
 27enum legacy_fs_param {
 28	LEGACY_FS_UNSET_PARAMS,
 29	LEGACY_FS_MONOLITHIC_PARAMS,
 30	LEGACY_FS_INDIVIDUAL_PARAMS,
 31};
 32
 33struct 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
 39static int legacy_init_fs_context(struct fs_context *fc);
 40
 41static 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
 50static 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 */
 61static 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 */
 94int 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}
109EXPORT_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 */
127int 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}
161EXPORT_SYMBOL(vfs_parse_fs_param);
162
163/**
164 * vfs_parse_fs_qstr - Convenience function to just parse a string.
165 * @fc: Filesystem context.
166 * @key: Parameter name.
167 * @value: Default value.
168 */
169int vfs_parse_fs_qstr(struct fs_context *fc, const char *key,
170			const struct qstr *value)
171{
172	int ret;
173
174	struct fs_parameter param = {
175		.key	= key,
176		.type	= fs_value_is_flag,
177		.size	= value ? value->len : 0,
178	};
179
180	if (value) {
181		param.string = kmemdup_nul(value->name, value->len, GFP_KERNEL);
182		if (!param.string)
183			return -ENOMEM;
184		param.type = fs_value_is_string;
185	}
186
187	ret = vfs_parse_fs_param(fc, &param);
188	kfree(param.string);
189	return ret;
190}
191EXPORT_SYMBOL(vfs_parse_fs_qstr);
192
193/**
194 * vfs_parse_monolithic_sep - Parse key[=val][,key[=val]]* mount data
195 * @fc: The superblock configuration to fill in.
196 * @data: The data to parse
197 * @sep: callback for separating next option
198 *
199 * Parse a blob of data that's in key[=val][,key[=val]]* form with a custom
200 * option separator callback.
201 *
202 * Returns 0 on success or the error returned by the ->parse_option() fs_context
203 * operation on failure.
204 */
205int vfs_parse_monolithic_sep(struct fs_context *fc, void *data,
206			     char *(*sep)(char **))
207{
208	char *options = data, *key;
209	int ret = 0;
210
211	if (!options)
212		return 0;
213
214	ret = security_sb_eat_lsm_opts(options, &fc->security);
215	if (ret)
216		return ret;
217
218	while ((key = sep(&options)) != NULL) {
219		if (*key) {
220			char *value = strchr(key, '=');
221
222			if (value) {
223				if (unlikely(value == key))
224					continue;
225				*value++ = 0;
226			}
227			ret = vfs_parse_fs_string(fc, key, value);
228			if (ret < 0)
229				break;
230		}
231	}
232
233	return ret;
234}
235EXPORT_SYMBOL(vfs_parse_monolithic_sep);
236
237static char *vfs_parse_comma_sep(char **s)
238{
239	return strsep(s, ",");
240}
241
242/**
243 * generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
244 * @fc: The superblock configuration to fill in.
245 * @data: The data to parse
246 *
247 * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
248 * called from the ->monolithic_mount_data() fs_context operation.
249 *
250 * Returns 0 on success or the error returned by the ->parse_option() fs_context
251 * operation on failure.
252 */
253int generic_parse_monolithic(struct fs_context *fc, void *data)
254{
255	return vfs_parse_monolithic_sep(fc, data, vfs_parse_comma_sep);
256}
257EXPORT_SYMBOL(generic_parse_monolithic);
258
259/**
260 * alloc_fs_context - Create a filesystem context.
261 * @fs_type: The filesystem type.
262 * @reference: The dentry from which this one derives (or NULL)
263 * @sb_flags: Filesystem/superblock flags (SB_*)
264 * @sb_flags_mask: Applicable members of @sb_flags
265 * @purpose: The purpose that this configuration shall be used for.
266 *
267 * Open a filesystem and create a mount context.  The mount context is
268 * initialised with the supplied flags and, if a submount/automount from
269 * another superblock (referred to by @reference) is supplied, may have
270 * parameters such as namespaces copied across from that superblock.
271 */
272static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
273				      struct dentry *reference,
274				      unsigned int sb_flags,
275				      unsigned int sb_flags_mask,
276				      enum fs_context_purpose purpose)
277{
278	int (*init_fs_context)(struct fs_context *);
279	struct fs_context *fc;
280	int ret = -ENOMEM;
281
282	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL_ACCOUNT);
283	if (!fc)
284		return ERR_PTR(-ENOMEM);
285
286	fc->purpose	= purpose;
287	fc->sb_flags	= sb_flags;
288	fc->sb_flags_mask = sb_flags_mask;
289	fc->fs_type	= get_filesystem(fs_type);
290	fc->cred	= get_current_cred();
291	fc->net_ns	= get_net(current->nsproxy->net_ns);
292	fc->log.prefix	= fs_type->name;
293
294	mutex_init(&fc->uapi_mutex);
295
296	switch (purpose) {
297	case FS_CONTEXT_FOR_MOUNT:
298		fc->user_ns = get_user_ns(fc->cred->user_ns);
299		break;
300	case FS_CONTEXT_FOR_SUBMOUNT:
301		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
302		break;
303	case FS_CONTEXT_FOR_RECONFIGURE:
304		atomic_inc(&reference->d_sb->s_active);
305		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
306		fc->root = dget(reference);
307		break;
308	}
309
310	/* TODO: Make all filesystems support this unconditionally */
311	init_fs_context = fc->fs_type->init_fs_context;
312	if (!init_fs_context)
313		init_fs_context = legacy_init_fs_context;
314
315	ret = init_fs_context(fc);
316	if (ret < 0)
317		goto err_fc;
318	fc->need_free = true;
319	return fc;
320
321err_fc:
322	put_fs_context(fc);
323	return ERR_PTR(ret);
324}
325
326struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
327					unsigned int sb_flags)
328{
329	return alloc_fs_context(fs_type, NULL, sb_flags, 0,
330					FS_CONTEXT_FOR_MOUNT);
331}
332EXPORT_SYMBOL(fs_context_for_mount);
333
334struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
335					unsigned int sb_flags,
336					unsigned int sb_flags_mask)
337{
338	return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
339				sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
340}
341EXPORT_SYMBOL(fs_context_for_reconfigure);
342
343/**
344 * fs_context_for_submount: allocate a new fs_context for a submount
345 * @type: file_system_type of the new context
346 * @reference: reference dentry from which to copy relevant info
347 *
348 * Allocate a new fs_context suitable for a submount. This also ensures that
349 * the fc->security object is inherited from @reference (if needed).
350 */
351struct fs_context *fs_context_for_submount(struct file_system_type *type,
352					   struct dentry *reference)
353{
354	struct fs_context *fc;
355	int ret;
356
357	fc = alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
358	if (IS_ERR(fc))
359		return fc;
360
361	ret = security_fs_context_submount(fc, reference->d_sb);
362	if (ret) {
363		put_fs_context(fc);
364		return ERR_PTR(ret);
365	}
366
367	return fc;
368}
369EXPORT_SYMBOL(fs_context_for_submount);
370
371void fc_drop_locked(struct fs_context *fc)
372{
373	struct super_block *sb = fc->root->d_sb;
374	dput(fc->root);
375	fc->root = NULL;
376	deactivate_locked_super(sb);
377}
378
379static void legacy_fs_context_free(struct fs_context *fc);
380
381/**
382 * vfs_dup_fs_context - Duplicate a filesystem context.
383 * @src_fc: The context to copy.
384 */
385struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
386{
387	struct fs_context *fc;
388	int ret;
389
390	if (!src_fc->ops->dup)
391		return ERR_PTR(-EOPNOTSUPP);
392
393	fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
394	if (!fc)
395		return ERR_PTR(-ENOMEM);
396
397	mutex_init(&fc->uapi_mutex);
398
399	fc->fs_private	= NULL;
400	fc->s_fs_info	= NULL;
401	fc->source	= NULL;
402	fc->security	= NULL;
403	get_filesystem(fc->fs_type);
404	get_net(fc->net_ns);
405	get_user_ns(fc->user_ns);
406	get_cred(fc->cred);
407	if (fc->log.log)
408		refcount_inc(&fc->log.log->usage);
409
410	/* Can't call put until we've called ->dup */
411	ret = fc->ops->dup(fc, src_fc);
412	if (ret < 0)
413		goto err_fc;
414
415	ret = security_fs_context_dup(fc, src_fc);
416	if (ret < 0)
417		goto err_fc;
418	return fc;
419
420err_fc:
421	put_fs_context(fc);
422	return ERR_PTR(ret);
423}
424EXPORT_SYMBOL(vfs_dup_fs_context);
425
426/**
427 * logfc - Log a message to a filesystem context
428 * @log: The filesystem context to log to, or NULL to use printk.
429 * @prefix: A string to prefix the output with, or NULL.
430 * @level: 'w' for a warning, 'e' for an error.  Anything else is a notice.
431 * @fmt: The format of the buffer.
432 */
433void logfc(struct fc_log *log, const char *prefix, char level, const char *fmt, ...)
434{
435	va_list va;
436	struct va_format vaf = {.fmt = fmt, .va = &va};
437
438	va_start(va, fmt);
439	if (!log) {
440		switch (level) {
441		case 'w':
442			printk(KERN_WARNING "%s%s%pV\n", prefix ? prefix : "",
443						prefix ? ": " : "", &vaf);
444			break;
445		case 'e':
446			printk(KERN_ERR "%s%s%pV\n", prefix ? prefix : "",
447						prefix ? ": " : "", &vaf);
448			break;
449		case 'i':
450			printk(KERN_INFO "%s%s%pV\n", prefix ? prefix : "",
451						prefix ? ": " : "", &vaf);
452			break;
453		default:
454			printk(KERN_NOTICE "%s%s%pV\n", prefix ? prefix : "",
455						prefix ? ": " : "", &vaf);
456			break;
457		}
458	} else {
459		unsigned int logsize = ARRAY_SIZE(log->buffer);
460		u8 index;
461		char *q = kasprintf(GFP_KERNEL, "%c %s%s%pV\n", level,
462						prefix ? prefix : "",
463						prefix ? ": " : "", &vaf);
464
465		index = log->head & (logsize - 1);
466		BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
467			     sizeof(log->tail) != sizeof(u8));
468		if ((u8)(log->head - log->tail) == logsize) {
469			/* The buffer is full, discard the oldest message */
470			if (log->need_free & (1 << index))
471				kfree(log->buffer[index]);
472			log->tail++;
473		}
474
475		log->buffer[index] = q ? q : "OOM: Can't store error string";
476		if (q)
477			log->need_free |= 1 << index;
478		else
479			log->need_free &= ~(1 << index);
480		log->head++;
481	}
482	va_end(va);
483}
484EXPORT_SYMBOL(logfc);
485
486/*
487 * Free a logging structure.
488 */
489static void put_fc_log(struct fs_context *fc)
490{
491	struct fc_log *log = fc->log.log;
492	int i;
493
494	if (log) {
495		if (refcount_dec_and_test(&log->usage)) {
496			fc->log.log = NULL;
497			for (i = 0; i < ARRAY_SIZE(log->buffer) ; i++)
498				if (log->need_free & (1 << i))
499					kfree(log->buffer[i]);
500			kfree(log);
501		}
502	}
503}
504
505/**
506 * put_fs_context - Dispose of a superblock configuration context.
507 * @fc: The context to dispose of.
508 */
509void put_fs_context(struct fs_context *fc)
510{
511	struct super_block *sb;
512
513	if (fc->root) {
514		sb = fc->root->d_sb;
515		dput(fc->root);
516		fc->root = NULL;
517		deactivate_super(sb);
518	}
519
520	if (fc->need_free && fc->ops && fc->ops->free)
521		fc->ops->free(fc);
522
523	security_free_mnt_opts(&fc->security);
524	put_net(fc->net_ns);
525	put_user_ns(fc->user_ns);
526	put_cred(fc->cred);
527	put_fc_log(fc);
528	put_filesystem(fc->fs_type);
529	kfree(fc->source);
530	kfree(fc);
531}
532EXPORT_SYMBOL(put_fs_context);
533
534/*
535 * Free the config for a filesystem that doesn't support fs_context.
536 */
537static void legacy_fs_context_free(struct fs_context *fc)
538{
539	struct legacy_fs_context *ctx = fc->fs_private;
540
541	if (ctx) {
542		if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
543			kfree(ctx->legacy_data);
544		kfree(ctx);
545	}
546}
547
548/*
549 * Duplicate a legacy config.
550 */
551static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
552{
553	struct legacy_fs_context *ctx;
554	struct legacy_fs_context *src_ctx = src_fc->fs_private;
555
556	ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
557	if (!ctx)
558		return -ENOMEM;
559
560	if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
561		ctx->legacy_data = kmemdup(src_ctx->legacy_data,
562					   src_ctx->data_size, GFP_KERNEL);
563		if (!ctx->legacy_data) {
564			kfree(ctx);
565			return -ENOMEM;
566		}
567	}
568
569	fc->fs_private = ctx;
570	return 0;
571}
572
573/*
574 * Add a parameter to a legacy config.  We build up a comma-separated list of
575 * options.
576 */
577static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
578{
579	struct legacy_fs_context *ctx = fc->fs_private;
580	unsigned int size = ctx->data_size;
581	size_t len = 0;
582	int ret;
583
584	ret = vfs_parse_fs_param_source(fc, param);
585	if (ret != -ENOPARAM)
586		return ret;
587
588	if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
589		return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
590
591	switch (param->type) {
592	case fs_value_is_string:
593		len = 1 + param->size;
594		fallthrough;
595	case fs_value_is_flag:
596		len += strlen(param->key);
597		break;
598	default:
599		return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
600			      param->key);
601	}
602
603	if (size + len + 2 > PAGE_SIZE)
604		return invalf(fc, "VFS: Legacy: Cumulative options too large");
605	if (strchr(param->key, ',') ||
606	    (param->type == fs_value_is_string &&
607	     memchr(param->string, ',', param->size)))
608		return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
609			      param->key);
610	if (!ctx->legacy_data) {
611		ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
612		if (!ctx->legacy_data)
613			return -ENOMEM;
614	}
615
616	if (size)
617		ctx->legacy_data[size++] = ',';
618	len = strlen(param->key);
619	memcpy(ctx->legacy_data + size, param->key, len);
620	size += len;
621	if (param->type == fs_value_is_string) {
622		ctx->legacy_data[size++] = '=';
623		memcpy(ctx->legacy_data + size, param->string, param->size);
624		size += param->size;
625	}
626	ctx->legacy_data[size] = '\0';
627	ctx->data_size = size;
628	ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
629	return 0;
630}
631
632/*
633 * Add monolithic mount data.
634 */
635static int legacy_parse_monolithic(struct fs_context *fc, void *data)
636{
637	struct legacy_fs_context *ctx = fc->fs_private;
638
639	if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
640		pr_warn("VFS: Can't mix monolithic and individual options\n");
641		return -EINVAL;
642	}
643
644	ctx->legacy_data = data;
645	ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
646	if (!ctx->legacy_data)
647		return 0;
648
649	if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
650		return 0;
651	return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
652}
653
654/*
655 * Get a mountable root with the legacy mount command.
656 */
657static int legacy_get_tree(struct fs_context *fc)
658{
659	struct legacy_fs_context *ctx = fc->fs_private;
660	struct super_block *sb;
661	struct dentry *root;
662
663	root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
664				      fc->source, ctx->legacy_data);
665	if (IS_ERR(root))
666		return PTR_ERR(root);
667
668	sb = root->d_sb;
669	BUG_ON(!sb);
670
671	fc->root = root;
672	return 0;
673}
674
675/*
676 * Handle remount.
677 */
678static int legacy_reconfigure(struct fs_context *fc)
679{
680	struct legacy_fs_context *ctx = fc->fs_private;
681	struct super_block *sb = fc->root->d_sb;
682
683	if (!sb->s_op->remount_fs)
684		return 0;
685
686	return sb->s_op->remount_fs(sb, &fc->sb_flags,
687				    ctx ? ctx->legacy_data : NULL);
688}
689
690const struct fs_context_operations legacy_fs_context_ops = {
691	.free			= legacy_fs_context_free,
692	.dup			= legacy_fs_context_dup,
693	.parse_param		= legacy_parse_param,
694	.parse_monolithic	= legacy_parse_monolithic,
695	.get_tree		= legacy_get_tree,
696	.reconfigure		= legacy_reconfigure,
697};
698
699/*
700 * Initialise a legacy context for a filesystem that doesn't support
701 * fs_context.
702 */
703static int legacy_init_fs_context(struct fs_context *fc)
704{
705	fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL_ACCOUNT);
706	if (!fc->fs_private)
707		return -ENOMEM;
708	fc->ops = &legacy_fs_context_ops;
709	return 0;
710}
711
712int parse_monolithic_mount_data(struct fs_context *fc, void *data)
713{
714	int (*monolithic_mount_data)(struct fs_context *, void *);
715
716	monolithic_mount_data = fc->ops->parse_monolithic;
717	if (!monolithic_mount_data)
718		monolithic_mount_data = generic_parse_monolithic;
719
720	return monolithic_mount_data(fc, data);
721}
722
723/*
724 * Clean up a context after performing an action on it and put it into a state
725 * from where it can be used to reconfigure a superblock.
726 *
727 * Note that here we do only the parts that can't fail; the rest is in
728 * finish_clean_context() below and in between those fs_context is marked
729 * FS_CONTEXT_AWAITING_RECONF.  The reason for splitup is that after
730 * successful mount or remount we need to report success to userland.
731 * Trying to do full reinit (for the sake of possible subsequent remount)
732 * and failing to allocate memory would've put us into a nasty situation.
733 * So here we only discard the old state and reinitialization is left
734 * until we actually try to reconfigure.
735 */
736void vfs_clean_context(struct fs_context *fc)
737{
738	if (fc->need_free && fc->ops && fc->ops->free)
739		fc->ops->free(fc);
740	fc->need_free = false;
741	fc->fs_private = NULL;
742	fc->s_fs_info = NULL;
743	fc->sb_flags = 0;
744	security_free_mnt_opts(&fc->security);
745	kfree(fc->source);
746	fc->source = NULL;
747	fc->exclusive = false;
748
749	fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
750	fc->phase = FS_CONTEXT_AWAITING_RECONF;
751}
752
753int finish_clean_context(struct fs_context *fc)
754{
755	int error;
756
757	if (fc->phase != FS_CONTEXT_AWAITING_RECONF)
758		return 0;
759
760	if (fc->fs_type->init_fs_context)
761		error = fc->fs_type->init_fs_context(fc);
762	else
763		error = legacy_init_fs_context(fc);
764	if (unlikely(error)) {
765		fc->phase = FS_CONTEXT_FAILED;
766		return error;
767	}
768	fc->need_free = true;
769	fc->phase = FS_CONTEXT_RECONF_PARAMS;
770	return 0;
771}