xref: /openbmc/linux/fs/fs_context.c (revision b9df3997) 
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 	{ "posixacl",	SB_POSIXACL },
46 	{ "ro",		SB_RDONLY },
47 	{ "sync",	SB_SYNCHRONOUS },
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 	{ "silent",	SB_SILENT },
56 };
57 
58 static const char *const forbidden_sb_flag[] = {
59 	"bind",
60 	"dev",
61 	"exec",
62 	"move",
63 	"noatime",
64 	"nodev",
65 	"nodiratime",
66 	"noexec",
67 	"norelatime",
68 	"nostrictatime",
69 	"nosuid",
70 	"private",
71 	"rec",
72 	"relatime",
73 	"remount",
74 	"shared",
75 	"slave",
76 	"strictatime",
77 	"suid",
78 	"unbindable",
79 };
80 
81 /*
82  * Check for a common mount option that manipulates s_flags.
83  */
84 static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
85 {
86 	unsigned int token;
87 	unsigned int i;
88 
89 	for (i = 0; i < ARRAY_SIZE(forbidden_sb_flag); i++)
90 		if (strcmp(key, forbidden_sb_flag[i]) == 0)
91 			return -EINVAL;
92 
93 	token = lookup_constant(common_set_sb_flag, key, 0);
94 	if (token) {
95 		fc->sb_flags |= token;
96 		fc->sb_flags_mask |= token;
97 		return 0;
98 	}
99 
100 	token = lookup_constant(common_clear_sb_flag, key, 0);
101 	if (token) {
102 		fc->sb_flags &= ~token;
103 		fc->sb_flags_mask |= token;
104 		return 0;
105 	}
106 
107 	return -ENOPARAM;
108 }
109 
110 /**
111  * vfs_parse_fs_param - Add a single parameter to a superblock config
112  * @fc: The filesystem context to modify
113  * @param: The parameter
114  *
115  * A single mount option in string form is applied to the filesystem context
116  * being set up.  Certain standard options (for example "ro") are translated
117  * into flag bits without going to the filesystem.  The active security module
118  * is allowed to observe and poach options.  Any other options are passed over
119  * to the filesystem to parse.
120  *
121  * This may be called multiple times for a context.
122  *
123  * Returns 0 on success and a negative error code on failure.  In the event of
124  * failure, supplementary error information may have been set.
125  */
126 int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
127 {
128 	int ret;
129 
130 	if (!param->key)
131 		return invalf(fc, "Unnamed parameter\n");
132 
133 	ret = vfs_parse_sb_flag(fc, param->key);
134 	if (ret != -ENOPARAM)
135 		return ret;
136 
137 	ret = security_fs_context_parse_param(fc, param);
138 	if (ret != -ENOPARAM)
139 		/* Param belongs to the LSM or is disallowed by the LSM; so
140 		 * don't pass to the FS.
141 		 */
142 		return ret;
143 
144 	if (fc->ops->parse_param) {
145 		ret = fc->ops->parse_param(fc, param);
146 		if (ret != -ENOPARAM)
147 			return ret;
148 	}
149 
150 	/* If the filesystem doesn't take any arguments, give it the
151 	 * default handling of source.
152 	 */
153 	if (strcmp(param->key, "source") == 0) {
154 		if (param->type != fs_value_is_string)
155 			return invalf(fc, "VFS: Non-string source");
156 		if (fc->source)
157 			return invalf(fc, "VFS: Multiple sources");
158 		fc->source = param->string;
159 		param->string = NULL;
160 		return 0;
161 	}
162 
163 	return invalf(fc, "%s: Unknown parameter '%s'",
164 		      fc->fs_type->name, param->key);
165 }
166 EXPORT_SYMBOL(vfs_parse_fs_param);
167 
168 /**
169  * vfs_parse_fs_string - Convenience function to just parse a string.
170  */
171 int vfs_parse_fs_string(struct fs_context *fc, const char *key,
172 			const char *value, size_t v_size)
173 {
174 	int ret;
175 
176 	struct fs_parameter param = {
177 		.key	= key,
178 		.type	= fs_value_is_string,
179 		.size	= v_size,
180 	};
181 
182 	if (v_size > 0) {
183 		param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
184 		if (!param.string)
185 			return -ENOMEM;
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  * generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
196  * @ctx: The superblock configuration to fill in.
197  * @data: The data to parse
198  *
199  * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
200  * called from the ->monolithic_mount_data() fs_context operation.
201  *
202  * Returns 0 on success or the error returned by the ->parse_option() fs_context
203  * operation on failure.
204  */
205 int generic_parse_monolithic(struct fs_context *fc, void *data)
206 {
207 	char *options = data, *key;
208 	int ret = 0;
209 
210 	if (!options)
211 		return 0;
212 
213 	ret = security_sb_eat_lsm_opts(options, &fc->security);
214 	if (ret)
215 		return ret;
216 
217 	while ((key = strsep(&options, ",")) != NULL) {
218 		if (*key) {
219 			size_t v_len = 0;
220 			char *value = strchr(key, '=');
221 
222 			if (value) {
223 				if (value == key)
224 					continue;
225 				*value++ = 0;
226 				v_len = strlen(value);
227 			}
228 			ret = vfs_parse_fs_string(fc, key, value, v_len);
229 			if (ret < 0)
230 				break;
231 		}
232 	}
233 
234 	return ret;
235 }
236 EXPORT_SYMBOL(generic_parse_monolithic);
237 
238 /**
239  * alloc_fs_context - Create a filesystem context.
240  * @fs_type: The filesystem type.
241  * @reference: The dentry from which this one derives (or NULL)
242  * @sb_flags: Filesystem/superblock flags (SB_*)
243  * @sb_flags_mask: Applicable members of @sb_flags
244  * @purpose: The purpose that this configuration shall be used for.
245  *
246  * Open a filesystem and create a mount context.  The mount context is
247  * initialised with the supplied flags and, if a submount/automount from
248  * another superblock (referred to by @reference) is supplied, may have
249  * parameters such as namespaces copied across from that superblock.
250  */
251 static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
252 				      struct dentry *reference,
253 				      unsigned int sb_flags,
254 				      unsigned int sb_flags_mask,
255 				      enum fs_context_purpose purpose)
256 {
257 	int (*init_fs_context)(struct fs_context *);
258 	struct fs_context *fc;
259 	int ret = -ENOMEM;
260 
261 	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
262 	if (!fc)
263 		return ERR_PTR(-ENOMEM);
264 
265 	fc->purpose	= purpose;
266 	fc->sb_flags	= sb_flags;
267 	fc->sb_flags_mask = sb_flags_mask;
268 	fc->fs_type	= get_filesystem(fs_type);
269 	fc->cred	= get_current_cred();
270 	fc->net_ns	= get_net(current->nsproxy->net_ns);
271 
272 	mutex_init(&fc->uapi_mutex);
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 		atomic_inc(&reference->d_sb->s_active);
283 		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
284 		fc->root = dget(reference);
285 		break;
286 	}
287 
288 	/* TODO: Make all filesystems support this unconditionally */
289 	init_fs_context = fc->fs_type->init_fs_context;
290 	if (!init_fs_context)
291 		init_fs_context = legacy_init_fs_context;
292 
293 	ret = init_fs_context(fc);
294 	if (ret < 0)
295 		goto err_fc;
296 	fc->need_free = true;
297 	return fc;
298 
299 err_fc:
300 	put_fs_context(fc);
301 	return ERR_PTR(ret);
302 }
303 
304 struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
305 					unsigned int sb_flags)
306 {
307 	return alloc_fs_context(fs_type, NULL, sb_flags, 0,
308 					FS_CONTEXT_FOR_MOUNT);
309 }
310 EXPORT_SYMBOL(fs_context_for_mount);
311 
312 struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
313 					unsigned int sb_flags,
314 					unsigned int sb_flags_mask)
315 {
316 	return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
317 				sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
318 }
319 EXPORT_SYMBOL(fs_context_for_reconfigure);
320 
321 struct fs_context *fs_context_for_submount(struct file_system_type *type,
322 					   struct dentry *reference)
323 {
324 	return alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
325 }
326 EXPORT_SYMBOL(fs_context_for_submount);
327 
328 void fc_drop_locked(struct fs_context *fc)
329 {
330 	struct super_block *sb = fc->root->d_sb;
331 	dput(fc->root);
332 	fc->root = NULL;
333 	deactivate_locked_super(sb);
334 }
335 
336 static void legacy_fs_context_free(struct fs_context *fc);
337 
338 /**
339  * vfs_dup_fc_config: Duplicate a filesystem context.
340  * @src_fc: The context to copy.
341  */
342 struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
343 {
344 	struct fs_context *fc;
345 	int ret;
346 
347 	if (!src_fc->ops->dup)
348 		return ERR_PTR(-EOPNOTSUPP);
349 
350 	fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
351 	if (!fc)
352 		return ERR_PTR(-ENOMEM);
353 
354 	mutex_init(&fc->uapi_mutex);
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 	if (fc->log)
365 		refcount_inc(&fc->log->usage);
366 
367 	/* Can't call put until we've called ->dup */
368 	ret = fc->ops->dup(fc, src_fc);
369 	if (ret < 0)
370 		goto err_fc;
371 
372 	ret = security_fs_context_dup(fc, src_fc);
373 	if (ret < 0)
374 		goto err_fc;
375 	return fc;
376 
377 err_fc:
378 	put_fs_context(fc);
379 	return ERR_PTR(ret);
380 }
381 EXPORT_SYMBOL(vfs_dup_fs_context);
382 
383 /**
384  * logfc - Log a message to a filesystem context
385  * @fc: The filesystem context to log to.
386  * @fmt: The format of the buffer.
387  */
388 void logfc(struct fs_context *fc, const char *fmt, ...)
389 {
390 	static const char store_failure[] = "OOM: Can't store error string";
391 	struct fc_log *log = fc ? fc->log : NULL;
392 	const char *p;
393 	va_list va;
394 	char *q;
395 	u8 freeable;
396 
397 	va_start(va, fmt);
398 	if (!strchr(fmt, '%')) {
399 		p = fmt;
400 		goto unformatted_string;
401 	}
402 	if (strcmp(fmt, "%s") == 0) {
403 		p = va_arg(va, const char *);
404 		goto unformatted_string;
405 	}
406 
407 	q = kvasprintf(GFP_KERNEL, fmt, va);
408 copied_string:
409 	if (!q)
410 		goto store_failure;
411 	freeable = 1;
412 	goto store_string;
413 
414 unformatted_string:
415 	if ((unsigned long)p >= (unsigned long)__start_rodata &&
416 	    (unsigned long)p <  (unsigned long)__end_rodata)
417 		goto const_string;
418 	if (log && within_module_core((unsigned long)p, log->owner))
419 		goto const_string;
420 	q = kstrdup(p, GFP_KERNEL);
421 	goto copied_string;
422 
423 store_failure:
424 	p = store_failure;
425 const_string:
426 	q = (char *)p;
427 	freeable = 0;
428 store_string:
429 	if (!log) {
430 		switch (fmt[0]) {
431 		case 'w':
432 			printk(KERN_WARNING "%s\n", q + 2);
433 			break;
434 		case 'e':
435 			printk(KERN_ERR "%s\n", q + 2);
436 			break;
437 		default:
438 			printk(KERN_NOTICE "%s\n", q + 2);
439 			break;
440 		}
441 		if (freeable)
442 			kfree(q);
443 	} else {
444 		unsigned int logsize = ARRAY_SIZE(log->buffer);
445 		u8 index;
446 
447 		index = log->head & (logsize - 1);
448 		BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
449 			     sizeof(log->tail) != sizeof(u8));
450 		if ((u8)(log->head - log->tail) == logsize) {
451 			/* The buffer is full, discard the oldest message */
452 			if (log->need_free & (1 << index))
453 				kfree(log->buffer[index]);
454 			log->tail++;
455 		}
456 
457 		log->buffer[index] = q;
458 		log->need_free &= ~(1 << index);
459 		log->need_free |= freeable << index;
460 		log->head++;
461 	}
462 	va_end(va);
463 }
464 EXPORT_SYMBOL(logfc);
465 
466 /*
467  * Free a logging structure.
468  */
469 static void put_fc_log(struct fs_context *fc)
470 {
471 	struct fc_log *log = fc->log;
472 	int i;
473 
474 	if (log) {
475 		if (refcount_dec_and_test(&log->usage)) {
476 			fc->log = NULL;
477 			for (i = 0; i <= 7; i++)
478 				if (log->need_free & (1 << i))
479 					kfree(log->buffer[i]);
480 			kfree(log);
481 		}
482 	}
483 }
484 
485 /**
486  * put_fs_context - Dispose of a superblock configuration context.
487  * @fc: The context to dispose of.
488  */
489 void put_fs_context(struct fs_context *fc)
490 {
491 	struct super_block *sb;
492 
493 	if (fc->root) {
494 		sb = fc->root->d_sb;
495 		dput(fc->root);
496 		fc->root = NULL;
497 		deactivate_super(sb);
498 	}
499 
500 	if (fc->need_free && fc->ops && fc->ops->free)
501 		fc->ops->free(fc);
502 
503 	security_free_mnt_opts(&fc->security);
504 	put_net(fc->net_ns);
505 	put_user_ns(fc->user_ns);
506 	put_cred(fc->cred);
507 	put_fc_log(fc);
508 	put_filesystem(fc->fs_type);
509 	kfree(fc->source);
510 	kfree(fc);
511 }
512 EXPORT_SYMBOL(put_fs_context);
513 
514 /*
515  * Free the config for a filesystem that doesn't support fs_context.
516  */
517 static void legacy_fs_context_free(struct fs_context *fc)
518 {
519 	struct legacy_fs_context *ctx = fc->fs_private;
520 
521 	if (ctx) {
522 		if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
523 			kfree(ctx->legacy_data);
524 		kfree(ctx);
525 	}
526 }
527 
528 /*
529  * Duplicate a legacy config.
530  */
531 static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
532 {
533 	struct legacy_fs_context *ctx;
534 	struct legacy_fs_context *src_ctx = src_fc->fs_private;
535 
536 	ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
537 	if (!ctx)
538 		return -ENOMEM;
539 
540 	if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
541 		ctx->legacy_data = kmemdup(src_ctx->legacy_data,
542 					   src_ctx->data_size, GFP_KERNEL);
543 		if (!ctx->legacy_data) {
544 			kfree(ctx);
545 			return -ENOMEM;
546 		}
547 	}
548 
549 	fc->fs_private = ctx;
550 	return 0;
551 }
552 
553 /*
554  * Add a parameter to a legacy config.  We build up a comma-separated list of
555  * options.
556  */
557 static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
558 {
559 	struct legacy_fs_context *ctx = fc->fs_private;
560 	unsigned int size = ctx->data_size;
561 	size_t len = 0;
562 
563 	if (strcmp(param->key, "source") == 0) {
564 		if (param->type != fs_value_is_string)
565 			return invalf(fc, "VFS: Legacy: Non-string source");
566 		if (fc->source)
567 			return invalf(fc, "VFS: Legacy: Multiple sources");
568 		fc->source = param->string;
569 		param->string = NULL;
570 		return 0;
571 	}
572 
573 	if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
574 		return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
575 
576 	switch (param->type) {
577 	case fs_value_is_string:
578 		len = 1 + param->size;
579 		/* Fall through */
580 	case fs_value_is_flag:
581 		len += strlen(param->key);
582 		break;
583 	default:
584 		return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
585 			      param->key);
586 	}
587 
588 	if (len > PAGE_SIZE - 2 - size)
589 		return invalf(fc, "VFS: Legacy: Cumulative options too large");
590 	if (strchr(param->key, ',') ||
591 	    (param->type == fs_value_is_string &&
592 	     memchr(param->string, ',', param->size)))
593 		return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
594 			      param->key);
595 	if (!ctx->legacy_data) {
596 		ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
597 		if (!ctx->legacy_data)
598 			return -ENOMEM;
599 	}
600 
601 	ctx->legacy_data[size++] = ',';
602 	len = strlen(param->key);
603 	memcpy(ctx->legacy_data + size, param->key, len);
604 	size += len;
605 	if (param->type == fs_value_is_string) {
606 		ctx->legacy_data[size++] = '=';
607 		memcpy(ctx->legacy_data + size, param->string, param->size);
608 		size += param->size;
609 	}
610 	ctx->legacy_data[size] = '\0';
611 	ctx->data_size = size;
612 	ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
613 	return 0;
614 }
615 
616 /*
617  * Add monolithic mount data.
618  */
619 static int legacy_parse_monolithic(struct fs_context *fc, void *data)
620 {
621 	struct legacy_fs_context *ctx = fc->fs_private;
622 
623 	if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
624 		pr_warn("VFS: Can't mix monolithic and individual options\n");
625 		return -EINVAL;
626 	}
627 
628 	ctx->legacy_data = data;
629 	ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
630 	if (!ctx->legacy_data)
631 		return 0;
632 
633 	if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
634 		return 0;
635 	return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
636 }
637 
638 /*
639  * Get a mountable root with the legacy mount command.
640  */
641 static int legacy_get_tree(struct fs_context *fc)
642 {
643 	struct legacy_fs_context *ctx = fc->fs_private;
644 	struct super_block *sb;
645 	struct dentry *root;
646 
647 	root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
648 				      fc->source, ctx->legacy_data);
649 	if (IS_ERR(root))
650 		return PTR_ERR(root);
651 
652 	sb = root->d_sb;
653 	BUG_ON(!sb);
654 
655 	fc->root = root;
656 	return 0;
657 }
658 
659 /*
660  * Handle remount.
661  */
662 static int legacy_reconfigure(struct fs_context *fc)
663 {
664 	struct legacy_fs_context *ctx = fc->fs_private;
665 	struct super_block *sb = fc->root->d_sb;
666 
667 	if (!sb->s_op->remount_fs)
668 		return 0;
669 
670 	return sb->s_op->remount_fs(sb, &fc->sb_flags,
671 				    ctx ? ctx->legacy_data : NULL);
672 }
673 
674 const struct fs_context_operations legacy_fs_context_ops = {
675 	.free			= legacy_fs_context_free,
676 	.dup			= legacy_fs_context_dup,
677 	.parse_param		= legacy_parse_param,
678 	.parse_monolithic	= legacy_parse_monolithic,
679 	.get_tree		= legacy_get_tree,
680 	.reconfigure		= legacy_reconfigure,
681 };
682 
683 /*
684  * Initialise a legacy context for a filesystem that doesn't support
685  * fs_context.
686  */
687 static int legacy_init_fs_context(struct fs_context *fc)
688 {
689 	fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL);
690 	if (!fc->fs_private)
691 		return -ENOMEM;
692 	fc->ops = &legacy_fs_context_ops;
693 	return 0;
694 }
695 
696 int parse_monolithic_mount_data(struct fs_context *fc, void *data)
697 {
698 	int (*monolithic_mount_data)(struct fs_context *, void *);
699 
700 	monolithic_mount_data = fc->ops->parse_monolithic;
701 	if (!monolithic_mount_data)
702 		monolithic_mount_data = generic_parse_monolithic;
703 
704 	return monolithic_mount_data(fc, data);
705 }
706 
707 /*
708  * Clean up a context after performing an action on it and put it into a state
709  * from where it can be used to reconfigure a superblock.
710  *
711  * Note that here we do only the parts that can't fail; the rest is in
712  * finish_clean_context() below and in between those fs_context is marked
713  * FS_CONTEXT_AWAITING_RECONF.  The reason for splitup is that after
714  * successful mount or remount we need to report success to userland.
715  * Trying to do full reinit (for the sake of possible subsequent remount)
716  * and failing to allocate memory would've put us into a nasty situation.
717  * So here we only discard the old state and reinitialization is left
718  * until we actually try to reconfigure.
719  */
720 void vfs_clean_context(struct fs_context *fc)
721 {
722 	if (fc->need_free && fc->ops && fc->ops->free)
723 		fc->ops->free(fc);
724 	fc->need_free = false;
725 	fc->fs_private = NULL;
726 	fc->s_fs_info = NULL;
727 	fc->sb_flags = 0;
728 	security_free_mnt_opts(&fc->security);
729 	kfree(fc->source);
730 	fc->source = NULL;
731 
732 	fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
733 	fc->phase = FS_CONTEXT_AWAITING_RECONF;
734 }
735 
736 int finish_clean_context(struct fs_context *fc)
737 {
738 	int error;
739 
740 	if (fc->phase != FS_CONTEXT_AWAITING_RECONF)
741 		return 0;
742 
743 	if (fc->fs_type->init_fs_context)
744 		error = fc->fs_type->init_fs_context(fc);
745 	else
746 		error = legacy_init_fs_context(fc);
747 	if (unlikely(error)) {
748 		fc->phase = FS_CONTEXT_FAILED;
749 		return error;
750 	}
751 	fc->need_free = true;
752 	fc->phase = FS_CONTEXT_RECONF_PARAMS;
753 	return 0;
754 }
755