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  * @fc: Filesystem context.
 166  * @key: Parameter name.
 167  * @value: Default value.
 168  * @v_size: Maximum number of bytes in the value.
 169  */
 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  */
 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
 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  */
 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  */
 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
 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
 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  */
 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
 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  */
 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  */
 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  */
 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  */
 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  */
 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  */
 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  */
 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  */
 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  */
 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  */
 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  */
 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
 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  */
 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
 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 }