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         { "posixacl",   SB_POSIXACL },
  46         { "ro",         SB_RDONLY },
  47         { "sync",       SB_SYNCHRONOUS },
  48         { },
  49 };
  50
  51 static const struct constant_table common_clear_sb_flag[] = {
  52         { "async",      SB_SYNCHRONOUS },
  53         { "nolazytime", SB_LAZYTIME },
  54         { "nomand",     SB_MANDLOCK },
  55         { "rw",         SB_RDONLY },
  56         { "silent",     SB_SILENT },
  57         { },
  58 };
  59
  60 static const char *const forbidden_sb_flag[] = {
  61         "bind",
  62         "dev",
  63         "exec",
  64         "move",
  65         "noatime",
  66         "nodev",
  67         "nodiratime",
  68         "noexec",
  69         "norelatime",
  70         "nostrictatime",
  71         "nosuid",
  72         "private",
  73         "rec",
  74         "relatime",
  75         "remount",
  76         "shared",
  77         "slave",
  78         "strictatime",
  79         "suid",
  80         "unbindable",
  81 };
  82
  83 /*
  84  * Check for a common mount option that manipulates s_flags.
  85  */
  86 static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
  87 {
  88         unsigned int token;
  89         unsigned int i;
  90
  91         for (i = 0; i < ARRAY_SIZE(forbidden_sb_flag); i++)
  92                 if (strcmp(key, forbidden_sb_flag[i]) == 0)
  93                         return -EINVAL;
  94
  95         token = lookup_constant(common_set_sb_flag, key, 0);
  96         if (token) {
  97                 fc->sb_flags |= token;
  98                 fc->sb_flags_mask |= token;
  99                 return 0;
 100         }
 101
 102         token = lookup_constant(common_clear_sb_flag, key, 0);
 103         if (token) {
 104                 fc->sb_flags &= ~token;
 105                 fc->sb_flags_mask |= token;
 106                 return 0;
 107         }
 108
 109         return -ENOPARAM;
 110 }
 111
 112 /**
 113  * vfs_parse_fs_param - Add a single parameter to a superblock config
 114  * @fc: The filesystem context to modify
 115  * @param: The parameter
 116  *
 117  * A single mount option in string form is applied to the filesystem context
 118  * being set up.  Certain standard options (for example "ro") are translated
 119  * into flag bits without going to the filesystem.  The active security module
 120  * is allowed to observe and poach options.  Any other options are passed over
 121  * to the filesystem to parse.
 122  *
 123  * This may be called multiple times for a context.
 124  *
 125  * Returns 0 on success and a negative error code on failure.  In the event of
 126  * failure, supplementary error information may have been set.
 127  */
 128 int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
 129 {
 130         int ret;
 131
 132         if (!param->key)
 133                 return invalf(fc, "Unnamed parameter\n");
 134
 135         ret = vfs_parse_sb_flag(fc, param->key);
 136         if (ret != -ENOPARAM)
 137                 return ret;
 138
 139         ret = security_fs_context_parse_param(fc, param);
 140         if (ret != -ENOPARAM)
 141                 /* Param belongs to the LSM or is disallowed by the LSM; so
 142                  * don't pass to the FS.
 143                  */
 144                 return ret;
 145
 146         if (fc->ops->parse_param) {
 147                 ret = fc->ops->parse_param(fc, param);
 148                 if (ret != -ENOPARAM)
 149                         return ret;
 150         }
 151
 152         /* If the filesystem doesn't take any arguments, give it the
 153          * default handling of source.
 154          */
 155         if (strcmp(param->key, "source") == 0) {
 156                 if (param->type != fs_value_is_string)
 157                         return invalf(fc, "VFS: Non-string source");
 158                 if (fc->source)
 159                         return invalf(fc, "VFS: Multiple sources");
 160                 fc->source = param->string;
 161                 param->string = NULL;
 162                 return 0;
 163         }
 164
 165         return invalf(fc, "%s: Unknown parameter '%s'",
 166                       fc->fs_type->name, param->key);
 167 }
 168 EXPORT_SYMBOL(vfs_parse_fs_param);
 169
 170 /**
 171  * vfs_parse_fs_string - Convenience function to just parse a string.
 172  */
 173 int vfs_parse_fs_string(struct fs_context *fc, const char *key,
 174                         const char *value, size_t v_size)
 175 {
 176         int ret;
 177
 178         struct fs_parameter param = {
 179                 .key    = key,
 180                 .type   = fs_value_is_flag,
 181                 .size   = v_size,
 182         };
 183
 184         if (value) {
 185                 param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
 186                 if (!param.string)
 187                         return -ENOMEM;
 188                 param.type = fs_value_is_string;
 189         }
 190
 191         ret = vfs_parse_fs_param(fc, &param);
 192         kfree(param.string);
 193         return ret;
 194 }
 195 EXPORT_SYMBOL(vfs_parse_fs_string);
 196
 197 /**
 198  * generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
 199  * @ctx: The superblock configuration to fill in.
 200  * @data: The data to parse
 201  *
 202  * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
 203  * called from the ->monolithic_mount_data() fs_context operation.
 204  *
 205  * Returns 0 on success or the error returned by the ->parse_option() fs_context
 206  * operation on failure.
 207  */
 208 int generic_parse_monolithic(struct fs_context *fc, void *data)
 209 {
 210         char *options = data, *key;
 211         int ret = 0;
 212
 213         if (!options)
 214                 return 0;
 215
 216         ret = security_sb_eat_lsm_opts(options, &fc->security);
 217         if (ret)
 218                 return ret;
 219
 220         while ((key = strsep(&options, ",")) != NULL) {
 221                 if (*key) {
 222                         size_t v_len = 0;
 223                         char *value = strchr(key, '=');
 224
 225                         if (value) {
 226                                 if (value == key)
 227                                         continue;
 228                                 *value++ = 0;
 229                                 v_len = strlen(value);
 230                         }
 231                         ret = vfs_parse_fs_string(fc, key, value, v_len);
 232                         if (ret < 0)
 233                                 break;
 234                 }
 235         }
 236
 237         return ret;
 238 }
 239 EXPORT_SYMBOL(generic_parse_monolithic);
 240
 241 /**
 242  * alloc_fs_context - Create a filesystem context.
 243  * @fs_type: The filesystem type.
 244  * @reference: The dentry from which this one derives (or NULL)
 245  * @sb_flags: Filesystem/superblock flags (SB_*)
 246  * @sb_flags_mask: Applicable members of @sb_flags
 247  * @purpose: The purpose that this configuration shall be used for.
 248  *
 249  * Open a filesystem and create a mount context.  The mount context is
 250  * initialised with the supplied flags and, if a submount/automount from
 251  * another superblock (referred to by @reference) is supplied, may have
 252  * parameters such as namespaces copied across from that superblock.
 253  */
 254 static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
 255                                       struct dentry *reference,
 256                                       unsigned int sb_flags,
 257                                       unsigned int sb_flags_mask,
 258                                       enum fs_context_purpose purpose)
 259 {
 260         int (*init_fs_context)(struct fs_context *);
 261         struct fs_context *fc;
 262         int ret = -ENOMEM;
 263
 264         fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
 265         if (!fc)
 266                 return ERR_PTR(-ENOMEM);
 267
 268         fc->purpose     = purpose;
 269         fc->sb_flags    = sb_flags;
 270         fc->sb_flags_mask = sb_flags_mask;
 271         fc->fs_type     = get_filesystem(fs_type);
 272         fc->cred        = get_current_cred();
 273         fc->net_ns      = get_net(current->nsproxy->net_ns);
 274         fc->log.prefix  = fs_type->name;
 275
 276         mutex_init(&fc->uapi_mutex);
 277
 278         switch (purpose) {
 279         case FS_CONTEXT_FOR_MOUNT:
 280                 fc->user_ns = get_user_ns(fc->cred->user_ns);
 281                 break;
 282         case FS_CONTEXT_FOR_SUBMOUNT:
 283                 fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
 284                 break;
 285         case FS_CONTEXT_FOR_RECONFIGURE:
 286                 atomic_inc(&reference->d_sb->s_active);
 287                 fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
 288                 fc->root = dget(reference);
 289                 break;
 290         }
 291
 292         /* TODO: Make all filesystems support this unconditionally */
 293         init_fs_context = fc->fs_type->init_fs_context;
 294         if (!init_fs_context)
 295                 init_fs_context = legacy_init_fs_context;
 296
 297         ret = init_fs_context(fc);
 298         if (ret < 0)
 299                 goto err_fc;
 300         fc->need_free = true;
 301         return fc;
 302
 303 err_fc:
 304         put_fs_context(fc);
 305         return ERR_PTR(ret);
 306 }
 307
 308 struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
 309                                         unsigned int sb_flags)
 310 {
 311         return alloc_fs_context(fs_type, NULL, sb_flags, 0,
 312                                         FS_CONTEXT_FOR_MOUNT);
 313 }
 314 EXPORT_SYMBOL(fs_context_for_mount);
 315
 316 struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
 317                                         unsigned int sb_flags,
 318                                         unsigned int sb_flags_mask)
 319 {
 320         return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
 321                                 sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
 322 }
 323 EXPORT_SYMBOL(fs_context_for_reconfigure);
 324
 325 struct fs_context *fs_context_for_submount(struct file_system_type *type,
 326                                            struct dentry *reference)
 327 {
 328         return alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
 329 }
 330 EXPORT_SYMBOL(fs_context_for_submount);
 331
 332 void fc_drop_locked(struct fs_context *fc)
 333 {
 334         struct super_block *sb = fc->root->d_sb;
 335         dput(fc->root);
 336         fc->root = NULL;
 337         deactivate_locked_super(sb);
 338 }
 339
 340 static void legacy_fs_context_free(struct fs_context *fc);
 341
 342 /**
 343  * vfs_dup_fc_config: Duplicate a filesystem context.
 344  * @src_fc: The context to copy.
 345  */
 346 struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
 347 {
 348         struct fs_context *fc;
 349         int ret;
 350
 351         if (!src_fc->ops->dup)
 352                 return ERR_PTR(-EOPNOTSUPP);
 353
 354         fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
 355         if (!fc)
 356                 return ERR_PTR(-ENOMEM);
 357
 358         mutex_init(&fc->uapi_mutex);
 359
 360         fc->fs_private  = NULL;
 361         fc->s_fs_info   = NULL;
 362         fc->source      = NULL;
 363         fc->security    = NULL;
 364         get_filesystem(fc->fs_type);
 365         get_net(fc->net_ns);
 366         get_user_ns(fc->user_ns);
 367         get_cred(fc->cred);
 368         if (fc->log.log)
 369                 refcount_inc(&fc->log.log->usage);
 370
 371         /* Can't call put until we've called ->dup */
 372         ret = fc->ops->dup(fc, src_fc);
 373         if (ret < 0)
 374                 goto err_fc;
 375
 376         ret = security_fs_context_dup(fc, src_fc);
 377         if (ret < 0)
 378                 goto err_fc;
 379         return fc;
 380
 381 err_fc:
 382         put_fs_context(fc);
 383         return ERR_PTR(ret);
 384 }
 385 EXPORT_SYMBOL(vfs_dup_fs_context);
 386
 387 /**
 388  * logfc - Log a message to a filesystem context
 389  * @fc: The filesystem context to log to.
 390  * @fmt: The format of the buffer.
 391  */
 392 void logfc(struct fc_log *log, const char *prefix, char level, const char *fmt, ...)
 393 {
 394         va_list va;
 395         struct va_format vaf = {.fmt = fmt, .va = &va};
 396
 397         va_start(va, fmt);
 398         if (!log) {
 399                 switch (level) {
 400                 case 'w':
 401                         printk(KERN_WARNING "%s%s%pV\n", prefix ? prefix : "",
 402                                                 prefix ? ": " : "", &vaf);
 403                         break;
 404                 case 'e':
 405                         printk(KERN_ERR "%s%s%pV\n", prefix ? prefix : "",
 406                                                 prefix ? ": " : "", &vaf);
 407                         break;
 408                 default:
 409                         printk(KERN_NOTICE "%s%s%pV\n", prefix ? prefix : "",
 410                                                 prefix ? ": " : "", &vaf);
 411                         break;
 412                 }
 413         } else {
 414                 unsigned int logsize = ARRAY_SIZE(log->buffer);
 415                 u8 index;
 416                 char *q = kasprintf(GFP_KERNEL, "%c %s%s%pV\n", level,
 417                                                 prefix ? prefix : "",
 418                                                 prefix ? ": " : "", &vaf);
 419
 420                 index = log->head & (logsize - 1);
 421                 BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
 422                              sizeof(log->tail) != sizeof(u8));
 423                 if ((u8)(log->head - log->tail) == logsize) {
 424                         /* The buffer is full, discard the oldest message */
 425                         if (log->need_free & (1 << index))
 426                                 kfree(log->buffer[index]);
 427                         log->tail++;
 428                 }
 429
 430                 log->buffer[index] = q ? q : "OOM: Can't store error string";
 431                 if (q)
 432                         log->need_free |= 1 << index;
 433                 else
 434                         log->need_free &= ~(1 << index);
 435                 log->head++;
 436         }
 437         va_end(va);
 438 }
 439 EXPORT_SYMBOL(logfc);
 440
 441 /*
 442  * Free a logging structure.
 443  */
 444 static void put_fc_log(struct fs_context *fc)
 445 {
 446         struct fc_log *log = fc->log.log;
 447         int i;
 448
 449         if (log) {
 450                 if (refcount_dec_and_test(&log->usage)) {
 451                         fc->log.log = NULL;
 452                         for (i = 0; i <= 7; i++)
 453                                 if (log->need_free & (1 << i))
 454                                         kfree(log->buffer[i]);
 455                         kfree(log);
 456                 }
 457         }
 458 }
 459
 460 /**
 461  * put_fs_context - Dispose of a superblock configuration context.
 462  * @fc: The context to dispose of.
 463  */
 464 void put_fs_context(struct fs_context *fc)
 465 {
 466         struct super_block *sb;
 467
 468         if (fc->root) {
 469                 sb = fc->root->d_sb;
 470                 dput(fc->root);
 471                 fc->root = NULL;
 472                 deactivate_super(sb);
 473         }
 474
 475         if (fc->need_free && fc->ops && fc->ops->free)
 476                 fc->ops->free(fc);
 477
 478         security_free_mnt_opts(&fc->security);
 479         put_net(fc->net_ns);
 480         put_user_ns(fc->user_ns);
 481         put_cred(fc->cred);
 482         put_fc_log(fc);
 483         put_filesystem(fc->fs_type);
 484         kfree(fc->source);
 485         kfree(fc);
 486 }
 487 EXPORT_SYMBOL(put_fs_context);
 488
 489 /*
 490  * Free the config for a filesystem that doesn't support fs_context.
 491  */
 492 static void legacy_fs_context_free(struct fs_context *fc)
 493 {
 494         struct legacy_fs_context *ctx = fc->fs_private;
 495
 496         if (ctx) {
 497                 if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
 498                         kfree(ctx->legacy_data);
 499                 kfree(ctx);
 500         }
 501 }
 502
 503 /*
 504  * Duplicate a legacy config.
 505  */
 506 static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
 507 {
 508         struct legacy_fs_context *ctx;
 509         struct legacy_fs_context *src_ctx = src_fc->fs_private;
 510
 511         ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
 512         if (!ctx)
 513                 return -ENOMEM;
 514
 515         if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
 516                 ctx->legacy_data = kmemdup(src_ctx->legacy_data,
 517                                            src_ctx->data_size, GFP_KERNEL);
 518                 if (!ctx->legacy_data) {
 519                         kfree(ctx);
 520                         return -ENOMEM;
 521                 }
 522         }
 523
 524         fc->fs_private = ctx;
 525         return 0;
 526 }
 527
 528 /*
 529  * Add a parameter to a legacy config.  We build up a comma-separated list of
 530  * options.
 531  */
 532 static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
 533 {
 534         struct legacy_fs_context *ctx = fc->fs_private;
 535         unsigned int size = ctx->data_size;
 536         size_t len = 0;
 537
 538         if (strcmp(param->key, "source") == 0) {
 539                 if (param->type != fs_value_is_string)
 540                         return invalf(fc, "VFS: Legacy: Non-string source");
 541                 if (fc->source)
 542                         return invalf(fc, "VFS: Legacy: Multiple sources");
 543                 fc->source = param->string;
 544                 param->string = NULL;
 545                 return 0;
 546         }
 547
 548         if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
 549                 return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
 550
 551         switch (param->type) {
 552         case fs_value_is_string:
 553                 len = 1 + param->size;
 554                 /* Fall through */
 555         case fs_value_is_flag:
 556                 len += strlen(param->key);
 557                 break;
 558         default:
 559                 return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
 560                               param->key);
 561         }
 562
 563         if (len > PAGE_SIZE - 2 - size)
 564                 return invalf(fc, "VFS: Legacy: Cumulative options too large");
 565         if (strchr(param->key, ',') ||
 566             (param->type == fs_value_is_string &&
 567              memchr(param->string, ',', param->size)))
 568                 return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
 569                               param->key);
 570         if (!ctx->legacy_data) {
 571                 ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
 572                 if (!ctx->legacy_data)
 573                         return -ENOMEM;
 574         }
 575
 576         ctx->legacy_data[size++] = ',';
 577         len = strlen(param->key);
 578         memcpy(ctx->legacy_data + size, param->key, len);
 579         size += len;
 580         if (param->type == fs_value_is_string) {
 581                 ctx->legacy_data[size++] = '=';
 582                 memcpy(ctx->legacy_data + size, param->string, param->size);
 583                 size += param->size;
 584         }
 585         ctx->legacy_data[size] = '\0';
 586         ctx->data_size = size;
 587         ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
 588         return 0;
 589 }
 590
 591 /*
 592  * Add monolithic mount data.
 593  */
 594 static int legacy_parse_monolithic(struct fs_context *fc, void *data)
 595 {
 596         struct legacy_fs_context *ctx = fc->fs_private;
 597
 598         if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
 599                 pr_warn("VFS: Can't mix monolithic and individual options\n");
 600                 return -EINVAL;
 601         }
 602
 603         ctx->legacy_data = data;
 604         ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
 605         if (!ctx->legacy_data)
 606                 return 0;
 607
 608         if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
 609                 return 0;
 610         return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
 611 }
 612
 613 /*
 614  * Get a mountable root with the legacy mount command.
 615  */
 616 static int legacy_get_tree(struct fs_context *fc)
 617 {
 618         struct legacy_fs_context *ctx = fc->fs_private;
 619         struct super_block *sb;
 620         struct dentry *root;
 621
 622         root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
 623                                       fc->source, ctx->legacy_data);
 624         if (IS_ERR(root))
 625                 return PTR_ERR(root);
 626
 627         sb = root->d_sb;
 628         BUG_ON(!sb);
 629
 630         fc->root = root;
 631         return 0;
 632 }
 633
 634 /*
 635  * Handle remount.
 636  */
 637 static int legacy_reconfigure(struct fs_context *fc)
 638 {
 639         struct legacy_fs_context *ctx = fc->fs_private;
 640         struct super_block *sb = fc->root->d_sb;
 641
 642         if (!sb->s_op->remount_fs)
 643                 return 0;
 644
 645         return sb->s_op->remount_fs(sb, &fc->sb_flags,
 646                                     ctx ? ctx->legacy_data : NULL);
 647 }
 648
 649 const struct fs_context_operations legacy_fs_context_ops = {
 650         .free                   = legacy_fs_context_free,
 651         .dup                    = legacy_fs_context_dup,
 652         .parse_param            = legacy_parse_param,
 653         .parse_monolithic       = legacy_parse_monolithic,
 654         .get_tree               = legacy_get_tree,
 655         .reconfigure            = legacy_reconfigure,
 656 };
 657
 658 /*
 659  * Initialise a legacy context for a filesystem that doesn't support
 660  * fs_context.
 661  */
 662 static int legacy_init_fs_context(struct fs_context *fc)
 663 {
 664         fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL);
 665         if (!fc->fs_private)
 666                 return -ENOMEM;
 667         fc->ops = &legacy_fs_context_ops;
 668         return 0;
 669 }
 670
 671 int parse_monolithic_mount_data(struct fs_context *fc, void *data)
 672 {
 673         int (*monolithic_mount_data)(struct fs_context *, void *);
 674
 675         monolithic_mount_data = fc->ops->parse_monolithic;
 676         if (!monolithic_mount_data)
 677                 monolithic_mount_data = generic_parse_monolithic;
 678
 679         return monolithic_mount_data(fc, data);
 680 }
 681
 682 /*
 683  * Clean up a context after performing an action on it and put it into a state
 684  * from where it can be used to reconfigure a superblock.
 685  *
 686  * Note that here we do only the parts that can't fail; the rest is in
 687  * finish_clean_context() below and in between those fs_context is marked
 688  * FS_CONTEXT_AWAITING_RECONF.  The reason for splitup is that after
 689  * successful mount or remount we need to report success to userland.
 690  * Trying to do full reinit (for the sake of possible subsequent remount)
 691  * and failing to allocate memory would've put us into a nasty situation.
 692  * So here we only discard the old state and reinitialization is left
 693  * until we actually try to reconfigure.
 694  */
 695 void vfs_clean_context(struct fs_context *fc)
 696 {
 697         if (fc->need_free && fc->ops && fc->ops->free)
 698                 fc->ops->free(fc);
 699         fc->need_free = false;
 700         fc->fs_private = NULL;
 701         fc->s_fs_info = NULL;
 702         fc->sb_flags = 0;
 703         security_free_mnt_opts(&fc->security);
 704         kfree(fc->source);
 705         fc->source = NULL;
 706
 707         fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
 708         fc->phase = FS_CONTEXT_AWAITING_RECONF;
 709 }
 710
 711 int finish_clean_context(struct fs_context *fc)
 712 {
 713         int error;
 714
 715         if (fc->phase != FS_CONTEXT_AWAITING_RECONF)
 716                 return 0;
 717
 718         if (fc->fs_type->init_fs_context)
 719                 error = fc->fs_type->init_fs_context(fc);
 720         else
 721                 error = legacy_init_fs_context(fc);
 722         if (unlikely(error)) {
 723                 fc->phase = FS_CONTEXT_FAILED;
 724                 return error;
 725         }
 726         fc->need_free = true;
 727         fc->phase = FS_CONTEXT_RECONF_PARAMS;
 728         return 0;
 729 }