fs/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
  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  */
  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  */
  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  */
 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  */
 166 int vfs_parse_fs_string(struct fs_context *fc, const char *key,
 167                         const char *value, size_t v_size)
 168 {
 169         int ret;
 170
 171         struct fs_parameter param = {
 172                 .key    = key,
 173                 .type   = fs_value_is_flag,
 174                 .size   = v_size,
 175         };
 176
 177         if (value) {
 178                 param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
 179                 if (!param.string)
 180                         return -ENOMEM;
 181                 param.type = fs_value_is_string;
 182         }
 183
 184         ret = vfs_parse_fs_param(fc, &param);
 185         kfree(param.string);
 186         return ret;
 187 }
 188 EXPORT_SYMBOL(vfs_parse_fs_string);
 189
 190 /**
 191  * generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
 192  * @ctx: The superblock configuration to fill in.
 193  * @data: The data to parse
 194  *
 195  * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
 196  * called from the ->monolithic_mount_data() fs_context operation.
 197  *
 198  * Returns 0 on success or the error returned by the ->parse_option() fs_context
 199  * operation on failure.
 200  */
 201 int generic_parse_monolithic(struct fs_context *fc, void *data)
 202 {
 203         char *options = data, *key;
 204         int ret = 0;
 205
 206         if (!options)
 207                 return 0;
 208
 209         ret = security_sb_eat_lsm_opts(options, &fc->security);
 210         if (ret)
 211                 return ret;
 212
 213         while ((key = strsep(&options, ",")) != NULL) {
 214                 if (*key) {
 215                         size_t v_len = 0;
 216                         char *value = strchr(key, '=');
 217
 218                         if (value) {
 219                                 if (value == key)
 220                                         continue;
 221                                 *value++ = 0;
 222                                 v_len = strlen(value);
 223                         }
 224                         ret = vfs_parse_fs_string(fc, key, value, v_len);
 225                         if (ret < 0)
 226                                 break;
 227                 }
 228         }
 229
 230         return ret;
 231 }
 232 EXPORT_SYMBOL(generic_parse_monolithic);
 233
 234 /**
 235  * alloc_fs_context - Create a filesystem context.
 236  * @fs_type: The filesystem type.
 237  * @reference: The dentry from which this one derives (or NULL)
 238  * @sb_flags: Filesystem/superblock flags (SB_*)
 239  * @sb_flags_mask: Applicable members of @sb_flags
 240  * @purpose: The purpose that this configuration shall be used for.
 241  *
 242  * Open a filesystem and create a mount context.  The mount context is
 243  * initialised with the supplied flags and, if a submount/automount from
 244  * another superblock (referred to by @reference) is supplied, may have
 245  * parameters such as namespaces copied across from that superblock.
 246  */
 247 static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
 248                                       struct dentry *reference,
 249                                       unsigned int sb_flags,
 250                                       unsigned int sb_flags_mask,
 251                                       enum fs_context_purpose purpose)
 252 {
 253         int (*init_fs_context)(struct fs_context *);
 254         struct fs_context *fc;
 255         int ret = -ENOMEM;
 256
 257         fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL_ACCOUNT);
 258         if (!fc)
 259                 return ERR_PTR(-ENOMEM);
 260
 261         fc->purpose     = purpose;
 262         fc->sb_flags    = sb_flags;
 263         fc->sb_flags_mask = sb_flags_mask;
 264         fc->fs_type     = get_filesystem(fs_type);
 265         fc->cred        = get_current_cred();
 266         fc->net_ns      = get_net(current->nsproxy->net_ns);
 267         fc->log.prefix  = fs_type->name;
 268
 269         mutex_init(&fc->uapi_mutex);
 270
 271         switch (purpose) {
 272         case FS_CONTEXT_FOR_MOUNT:
 273                 fc->user_ns = get_user_ns(fc->cred->user_ns);
 274                 break;
 275         case FS_CONTEXT_FOR_SUBMOUNT:
 276                 fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
 277                 break;
 278         case FS_CONTEXT_FOR_RECONFIGURE:
 279                 atomic_inc(&reference->d_sb->s_active);
 280                 fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
 281                 fc->root = dget(reference);
 282                 break;
 283         }
 284
 285         /* TODO: Make all filesystems support this unconditionally */
 286         init_fs_context = fc->fs_type->init_fs_context;
 287         if (!init_fs_context)
 288                 init_fs_context = legacy_init_fs_context;
 289
 290         ret = init_fs_context(fc);
 291         if (ret < 0)
 292                 goto err_fc;
 293         fc->need_free = true;
 294         return fc;
 295
 296 err_fc:
 297         put_fs_context(fc);
 298         return ERR_PTR(ret);
 299 }
 300
 301 struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
 302                                         unsigned int sb_flags)
 303 {
 304         return alloc_fs_context(fs_type, NULL, sb_flags, 0,
 305                                         FS_CONTEXT_FOR_MOUNT);
 306 }
 307 EXPORT_SYMBOL(fs_context_for_mount);
 308
 309 struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
 310                                         unsigned int sb_flags,
 311                                         unsigned int sb_flags_mask)
 312 {
 313         return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
 314                                 sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
 315 }
 316 EXPORT_SYMBOL(fs_context_for_reconfigure);
 317
 318 struct fs_context *fs_context_for_submount(struct file_system_type *type,
 319                                            struct dentry *reference)
 320 {
 321         return alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
 322 }
 323 EXPORT_SYMBOL(fs_context_for_submount);
 324
 325 void fc_drop_locked(struct fs_context *fc)
 326 {
 327         struct super_block *sb = fc->root->d_sb;
 328         dput(fc->root);
 329         fc->root = NULL;
 330         deactivate_locked_super(sb);
 331 }
 332
 333 static void legacy_fs_context_free(struct fs_context *fc);
 334
 335 /**
 336  * vfs_dup_fc_config: Duplicate a filesystem context.
 337  * @src_fc: The context to copy.
 338  */
 339 struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
 340 {
 341         struct fs_context *fc;
 342         int ret;
 343
 344         if (!src_fc->ops->dup)
 345                 return ERR_PTR(-EOPNOTSUPP);
 346
 347         fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
 348         if (!fc)
 349                 return ERR_PTR(-ENOMEM);
 350
 351         mutex_init(&fc->uapi_mutex);
 352
 353         fc->fs_private  = NULL;
 354         fc->s_fs_info   = NULL;
 355         fc->source      = NULL;
 356         fc->security    = NULL;
 357         get_filesystem(fc->fs_type);
 358         get_net(fc->net_ns);
 359         get_user_ns(fc->user_ns);
 360         get_cred(fc->cred);
 361         if (fc->log.log)
 362                 refcount_inc(&fc->log.log->usage);
 363
 364         /* Can't call put until we've called ->dup */
 365         ret = fc->ops->dup(fc, src_fc);
 366         if (ret < 0)
 367                 goto err_fc;
 368
 369         ret = security_fs_context_dup(fc, src_fc);
 370         if (ret < 0)
 371                 goto err_fc;
 372         return fc;
 373
 374 err_fc:
 375         put_fs_context(fc);
 376         return ERR_PTR(ret);
 377 }
 378 EXPORT_SYMBOL(vfs_dup_fs_context);
 379
 380 /**
 381  * logfc - Log a message to a filesystem context
 382  * @fc: The filesystem context to log to.
 383  * @fmt: The format of the buffer.
 384  */
 385 void logfc(struct fc_log *log, const char *prefix, char level, const char *fmt, ...)
 386 {
 387         va_list va;
 388         struct va_format vaf = {.fmt = fmt, .va = &va};
 389
 390         va_start(va, fmt);
 391         if (!log) {
 392                 switch (level) {
 393                 case 'w':
 394                         printk(KERN_WARNING "%s%s%pV\n", prefix ? prefix : "",
 395                                                 prefix ? ": " : "", &vaf);
 396                         break;
 397                 case 'e':
 398                         printk(KERN_ERR "%s%s%pV\n", prefix ? prefix : "",
 399                                                 prefix ? ": " : "", &vaf);
 400                         break;
 401                 default:
 402                         printk(KERN_NOTICE "%s%s%pV\n", prefix ? prefix : "",
 403                                                 prefix ? ": " : "", &vaf);
 404                         break;
 405                 }
 406         } else {
 407                 unsigned int logsize = ARRAY_SIZE(log->buffer);
 408                 u8 index;
 409                 char *q = kasprintf(GFP_KERNEL, "%c %s%s%pV\n", level,
 410                                                 prefix ? prefix : "",
 411                                                 prefix ? ": " : "", &vaf);
 412
 413                 index = log->head & (logsize - 1);
 414                 BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
 415                              sizeof(log->tail) != sizeof(u8));
 416                 if ((u8)(log->head - log->tail) == logsize) {
 417                         /* The buffer is full, discard the oldest message */
 418                         if (log->need_free & (1 << index))
 419                                 kfree(log->buffer[index]);
 420                         log->tail++;
 421                 }
 422
 423                 log->buffer[index] = q ? q : "OOM: Can't store error string";
 424                 if (q)
 425                         log->need_free |= 1 << index;
 426                 else
 427                         log->need_free &= ~(1 << index);
 428                 log->head++;
 429         }
 430         va_end(va);
 431 }
 432 EXPORT_SYMBOL(logfc);
 433
 434 /*
 435  * Free a logging structure.
 436  */
 437 static void put_fc_log(struct fs_context *fc)
 438 {
 439         struct fc_log *log = fc->log.log;
 440         int i;
 441
 442         if (log) {
 443                 if (refcount_dec_and_test(&log->usage)) {
 444                         fc->log.log = NULL;
 445                         for (i = 0; i <= 7; i++)
 446                                 if (log->need_free & (1 << i))
 447                                         kfree(log->buffer[i]);
 448                         kfree(log);
 449                 }
 450         }
 451 }
 452
 453 /**
 454  * put_fs_context - Dispose of a superblock configuration context.
 455  * @fc: The context to dispose of.
 456  */
 457 void put_fs_context(struct fs_context *fc)
 458 {
 459         struct super_block *sb;
 460
 461         if (fc->root) {
 462                 sb = fc->root->d_sb;
 463                 dput(fc->root);
 464                 fc->root = NULL;
 465                 deactivate_super(sb);
 466         }
 467
 468         if (fc->need_free && fc->ops && fc->ops->free)
 469                 fc->ops->free(fc);
 470
 471         security_free_mnt_opts(&fc->security);
 472         put_net(fc->net_ns);
 473         put_user_ns(fc->user_ns);
 474         put_cred(fc->cred);
 475         put_fc_log(fc);
 476         put_filesystem(fc->fs_type);
 477         kfree(fc->source);
 478         kfree(fc);
 479 }
 480 EXPORT_SYMBOL(put_fs_context);
 481
 482 /*
 483  * Free the config for a filesystem that doesn't support fs_context.
 484  */
 485 static void legacy_fs_context_free(struct fs_context *fc)
 486 {
 487         struct legacy_fs_context *ctx = fc->fs_private;
 488
 489         if (ctx) {
 490                 if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
 491                         kfree(ctx->legacy_data);
 492                 kfree(ctx);
 493         }
 494 }
 495
 496 /*
 497  * Duplicate a legacy config.
 498  */
 499 static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
 500 {
 501         struct legacy_fs_context *ctx;
 502         struct legacy_fs_context *src_ctx = src_fc->fs_private;
 503
 504         ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
 505         if (!ctx)
 506                 return -ENOMEM;
 507
 508         if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
 509                 ctx->legacy_data = kmemdup(src_ctx->legacy_data,
 510                                            src_ctx->data_size, GFP_KERNEL);
 511                 if (!ctx->legacy_data) {
 512                         kfree(ctx);
 513                         return -ENOMEM;
 514                 }
 515         }
 516
 517         fc->fs_private = ctx;
 518         return 0;
 519 }
 520
 521 /*
 522  * Add a parameter to a legacy config.  We build up a comma-separated list of
 523  * options.
 524  */
 525 static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
 526 {
 527         struct legacy_fs_context *ctx = fc->fs_private;
 528         unsigned int size = ctx->data_size;
 529         size_t len = 0;
 530         int ret;
 531
 532         ret = vfs_parse_fs_param_source(fc, param);
 533         if (ret != -ENOPARAM)
 534                 return ret;
 535
 536         if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
 537                 return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
 538
 539         switch (param->type) {
 540         case fs_value_is_string:
 541                 len = 1 + param->size;
 542                 fallthrough;
 543         case fs_value_is_flag:
 544                 len += strlen(param->key);
 545                 break;
 546         default:
 547                 return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
 548                               param->key);
 549         }
 550
 551         if (size + len + 2 > PAGE_SIZE)
 552                 return invalf(fc, "VFS: Legacy: Cumulative options too large");
 553         if (strchr(param->key, ',') ||
 554             (param->type == fs_value_is_string &&
 555              memchr(param->string, ',', param->size)))
 556                 return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
 557                               param->key);
 558         if (!ctx->legacy_data) {
 559                 ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
 560                 if (!ctx->legacy_data)
 561                         return -ENOMEM;
 562         }
 563
 564         ctx->legacy_data[size++] = ',';
 565         len = strlen(param->key);
 566         memcpy(ctx->legacy_data + size, param->key, len);
 567         size += len;
 568         if (param->type == fs_value_is_string) {
 569                 ctx->legacy_data[size++] = '=';
 570                 memcpy(ctx->legacy_data + size, param->string, param->size);
 571                 size += param->size;
 572         }
 573         ctx->legacy_data[size] = '\0';
 574         ctx->data_size = size;
 575         ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
 576         return 0;
 577 }
 578
 579 /*
 580  * Add monolithic mount data.
 581  */
 582 static int legacy_parse_monolithic(struct fs_context *fc, void *data)
 583 {
 584         struct legacy_fs_context *ctx = fc->fs_private;
 585
 586         if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
 587                 pr_warn("VFS: Can't mix monolithic and individual options\n");
 588                 return -EINVAL;
 589         }
 590
 591         ctx->legacy_data = data;
 592         ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
 593         if (!ctx->legacy_data)
 594                 return 0;
 595
 596         if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
 597                 return 0;
 598         return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
 599 }
 600
 601 /*
 602  * Get a mountable root with the legacy mount command.
 603  */
 604 static int legacy_get_tree(struct fs_context *fc)
 605 {
 606         struct legacy_fs_context *ctx = fc->fs_private;
 607         struct super_block *sb;
 608         struct dentry *root;
 609
 610         root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
 611                                       fc->source, ctx->legacy_data);
 612         if (IS_ERR(root))
 613                 return PTR_ERR(root);
 614
 615         sb = root->d_sb;
 616         BUG_ON(!sb);
 617
 618         fc->root = root;
 619         return 0;
 620 }
 621
 622 /*
 623  * Handle remount.
 624  */
 625 static int legacy_reconfigure(struct fs_context *fc)
 626 {
 627         struct legacy_fs_context *ctx = fc->fs_private;
 628         struct super_block *sb = fc->root->d_sb;
 629
 630         if (!sb->s_op->remount_fs)
 631                 return 0;
 632
 633         return sb->s_op->remount_fs(sb, &fc->sb_flags,
 634                                     ctx ? ctx->legacy_data : NULL);
 635 }
 636
 637 const struct fs_context_operations legacy_fs_context_ops = {
 638         .free                   = legacy_fs_context_free,
 639         .dup                    = legacy_fs_context_dup,
 640         .parse_param            = legacy_parse_param,
 641         .parse_monolithic       = legacy_parse_monolithic,
 642         .get_tree               = legacy_get_tree,
 643         .reconfigure            = legacy_reconfigure,
 644 };
 645
 646 /*
 647  * Initialise a legacy context for a filesystem that doesn't support
 648  * fs_context.
 649  */
 650 static int legacy_init_fs_context(struct fs_context *fc)
 651 {
 652         fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL_ACCOUNT);
 653         if (!fc->fs_private)
 654                 return -ENOMEM;
 655         fc->ops = &legacy_fs_context_ops;
 656         return 0;
 657 }
 658
 659 int parse_monolithic_mount_data(struct fs_context *fc, void *data)
 660 {
 661         int (*monolithic_mount_data)(struct fs_context *, void *);
 662
 663         monolithic_mount_data = fc->ops->parse_monolithic;
 664         if (!monolithic_mount_data)
 665                 monolithic_mount_data = generic_parse_monolithic;
 666
 667         return monolithic_mount_data(fc, data);
 668 }
 669
 670 /*
 671  * Clean up a context after performing an action on it and put it into a state
 672  * from where it can be used to reconfigure a superblock.
 673  *
 674  * Note that here we do only the parts that can't fail; the rest is in
 675  * finish_clean_context() below and in between those fs_context is marked
 676  * FS_CONTEXT_AWAITING_RECONF.  The reason for splitup is that after
 677  * successful mount or remount we need to report success to userland.
 678  * Trying to do full reinit (for the sake of possible subsequent remount)
 679  * and failing to allocate memory would've put us into a nasty situation.
 680  * So here we only discard the old state and reinitialization is left
 681  * until we actually try to reconfigure.
 682  */
 683 void vfs_clean_context(struct fs_context *fc)
 684 {
 685         if (fc->need_free && fc->ops && fc->ops->free)
 686                 fc->ops->free(fc);
 687         fc->need_free = false;
 688         fc->fs_private = NULL;
 689         fc->s_fs_info = NULL;
 690         fc->sb_flags = 0;
 691         security_free_mnt_opts(&fc->security);
 692         kfree(fc->source);
 693         fc->source = NULL;
 694
 695         fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
 696         fc->phase = FS_CONTEXT_AWAITING_RECONF;
 697 }
 698
 699 int finish_clean_context(struct fs_context *fc)
 700 {
 701         int error;
 702
 703         if (fc->phase != FS_CONTEXT_AWAITING_RECONF)
 704                 return 0;
 705
 706         if (fc->fs_type->init_fs_context)
 707                 error = fc->fs_type->init_fs_context(fc);
 708         else
 709                 error = legacy_init_fs_context(fc);
 710         if (unlikely(error)) {
 711                 fc->phase = FS_CONTEXT_FAILED;
 712                 return error;
 713         }
 714         fc->need_free = true;
 715         fc->phase = FS_CONTEXT_RECONF_PARAMS;
 716         return 0;
 717 }