Quelle fs_context.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-or-later
/* Provide a way to create a superblock configuration context within the kernel
* that allows a superblock to be set up prior to mounting.
*
* Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/magic.h>
#include <linux/security.h>
#include <linux/mnt_namespace.h>
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>
#include <net/net_namespace.h>
#include <asm/sections.h>
#include "mount.h"
#include "internal.h"

enum legacy_fs_param {
LEGACY_FS_UNSET_PARAMS,
LEGACY_FS_MONOLITHIC_PARAMS,
LEGACY_FS_INDIVIDUAL_PARAMS,
};

struct legacy_fs_context {
char   *legacy_data; /* Data page for legacy filesystems */
size_t   data_size;
enum legacy_fs_param param_type;
};

static int legacy_init_fs_context(struct fs_context *fc);

static const struct constant_table common_set_sb_flag[] = {
{ "dirsync", SB_DIRSYNC },
{ "lazytime", SB_LAZYTIME },
{ "mand", SB_MANDLOCK },
{ "ro",  SB_RDONLY },
{ "sync", SB_SYNCHRONOUS },
{ },
};

static const struct constant_table common_clear_sb_flag[] = {
{ "async", SB_SYNCHRONOUS },
{ "nolazytime", SB_LAZYTIME },
{ "nomand", SB_MANDLOCK },
{ "rw",  SB_RDONLY },
{ },
};

/*
* Check for a common mount option that manipulates s_flags.
*/
static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
{
unsigned int token;

token = lookup_constant(common_set_sb_flag, key, 0);
if (token) {
  fc->sb_flags |= token;
  fc->sb_flags_mask |= token;
  return 0;
}

token = lookup_constant(common_clear_sb_flag, key, 0);
if (token) {
  fc->sb_flags &= ~token;
  fc->sb_flags_mask |= token;
  return 0;
}

return -ENOPARAM;
}

/**
* vfs_parse_fs_param_source - Handle setting "source" via parameter
* @fc: The filesystem context to modify
* @param: The parameter
*
* This is a simple helper for filesystems to verify that the "source" they
* accept is sane.
*
* Returns 0 on success, -ENOPARAM if this is not  "source" parameter, and
* -EINVAL otherwise. In the event of failure, supplementary error information
*  is logged.
*/
int vfs_parse_fs_param_source(struct fs_context *fc, struct fs_parameter *param)
{
if (strcmp(param->key, "source") != 0)
  return -ENOPARAM;

if (param->type != fs_value_is_string)
  return invalf(fc, "Non-string source");

if (fc->source)
  return invalf(fc, "Multiple sources");

fc->source = param->string;
param->string = NULL;
return 0;
}
EXPORT_SYMBOL(vfs_parse_fs_param_source);

/**
* vfs_parse_fs_param - Add a single parameter to a superblock config
* @fc: The filesystem context to modify
* @param: The parameter
*
* A single mount option in string form is applied to the filesystem context
* being set up.  Certain standard options (for example "ro") are translated
* into flag bits without going to the filesystem.  The active security module
* is allowed to observe and poach options.  Any other options are passed over
* to the filesystem to parse.
*
* This may be called multiple times for a context.
*
* Returns 0 on success and a negative error code on failure.  In the event of
* failure, supplementary error information may have been set.
*/
int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
{
int ret;

if (!param->key)
  return invalf(fc, "Unnamed parameter\n");

ret = vfs_parse_sb_flag(fc, param->key);
if (ret != -ENOPARAM)
  return ret;

ret = security_fs_context_parse_param(fc, param);
if (ret != -ENOPARAM)
  /* Param belongs to the LSM or is disallowed by the LSM; so
* don't pass to the FS.
*/
  return ret;

if (fc->ops->parse_param) {
  ret = fc->ops->parse_param(fc, param);
  if (ret != -ENOPARAM)
   return ret;
}

/* If the filesystem doesn't take any arguments, give it the
* default handling of source.
*/
ret = vfs_parse_fs_param_source(fc, param);
if (ret != -ENOPARAM)
  return ret;

return invalf(fc, "%s: Unknown parameter '%s'",
        fc->fs_type->name, param->key);
}
EXPORT_SYMBOL(vfs_parse_fs_param);

/**
* vfs_parse_fs_string - Convenience function to just parse a string.
* @fc: Filesystem context.
* @key: Parameter name.
* @value: Default value.
* @v_size: Maximum number of bytes in the value.
*/
int vfs_parse_fs_string(struct fs_context *fc, const char *key,
   const char *value, size_t v_size)
{
int ret;

struct fs_parameter param = {
  .key = key,
  .type = fs_value_is_flag,
  .size = v_size,
};

if (value) {
  param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
  if (!param.string)
   return -ENOMEM;
  param.type = fs_value_is_string;
}

ret = vfs_parse_fs_param(fc, ¶m);
kfree(param.string);
return ret;
}
EXPORT_SYMBOL(vfs_parse_fs_string);

/**
* vfs_parse_monolithic_sep - Parse key[=val][,key[=val]]* mount data
* @fc: The superblock configuration to fill in.
* @data: The data to parse
* @sep: callback for separating next option
*
* Parse a blob of data that's in key[=val][,key[=val]]* form with a custom
* option separator callback.
*
* Returns 0 on success or the error returned by the ->parse_option() fs_context
* operation on failure.
*/
int vfs_parse_monolithic_sep(struct fs_context *fc, void *data,
        char *(*sep)(char **))
{
char *options = data, *key;
int ret = 0;

if (!options)
  return 0;

ret = security_sb_eat_lsm_opts(options, &fc->security);
if (ret)
  return ret;

while ((key = sep(&options)) != NULL) {
  if (*key) {
   size_t v_len = 0;
   char *value = strchr(key, '=');

   if (value) {
    if (unlikely(value == key))
     continue;
    *value++ = 0;
    v_len = strlen(value);
   }
   ret = vfs_parse_fs_string(fc, key, value, v_len);
   if (ret < 0)
    break;
  }
}

return ret;
}
EXPORT_SYMBOL(vfs_parse_monolithic_sep);

static char *vfs_parse_comma_sep(char **s)
{
return strsep(s, ",");
}

/**
* generic_parse_monolithic - Parse key[=val][,key[=val]]* mount data
* @fc: The superblock configuration to fill in.
* @data: The data to parse
*
* Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
* called from the ->monolithic_mount_data() fs_context operation.
*
* Returns 0 on success or the error returned by the ->parse_option() fs_context
* operation on failure.
*/
int generic_parse_monolithic(struct fs_context *fc, void *data)
{
return vfs_parse_monolithic_sep(fc, data, vfs_parse_comma_sep);
}
EXPORT_SYMBOL(generic_parse_monolithic);

/**
* alloc_fs_context - Create a filesystem context.
* @fs_type: The filesystem type.
* @reference: The dentry from which this one derives (or NULL)
* @sb_flags: Filesystem/superblock flags (SB_*)
* @sb_flags_mask: Applicable members of @sb_flags
* @purpose: The purpose that this configuration shall be used for.
*
* Open a filesystem and create a mount context.  The mount context is
* initialised with the supplied flags and, if a submount/automount from
* another superblock (referred to by @reference) is supplied, may have
* parameters such as namespaces copied across from that superblock.
*/
static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
          struct dentry *reference,
          unsigned int sb_flags,
          unsigned int sb_flags_mask,
          enum fs_context_purpose purpose)
{
int (*init_fs_context)(struct fs_context *);
struct fs_context *fc;
int ret = -ENOMEM;

fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL_ACCOUNT);
if (!fc)
  return ERR_PTR(-ENOMEM);

fc->purpose = purpose;
fc->sb_flags = sb_flags;
fc->sb_flags_mask = sb_flags_mask;
fc->fs_type = get_filesystem(fs_type);
fc->cred = get_current_cred();
fc->net_ns = get_net(current->nsproxy->net_ns);
fc->log.prefix = fs_type->name;

mutex_init(&fc->uapi_mutex);

switch (purpose) {
case FS_CONTEXT_FOR_MOUNT:
  fc->user_ns = get_user_ns(fc->cred->user_ns);
  break;
case FS_CONTEXT_FOR_SUBMOUNT:
  fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
  break;
case FS_CONTEXT_FOR_RECONFIGURE:
  atomic_inc(&reference->d_sb->s_active);
  fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
  fc->root = dget(reference);
  break;
}

/* TODO: Make all filesystems support this unconditionally */
init_fs_context = fc->fs_type->init_fs_context;
if (!init_fs_context)
  init_fs_context = legacy_init_fs_context;

ret = init_fs_context(fc);
if (ret < 0)
  goto err_fc;
fc->need_free = true;
return fc;

err_fc:
put_fs_context(fc);
return ERR_PTR(ret);
}

struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
     unsigned int sb_flags)
{
return alloc_fs_context(fs_type, NULL, sb_flags, 0,
     FS_CONTEXT_FOR_MOUNT);
}
EXPORT_SYMBOL(fs_context_for_mount);

struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
     unsigned int sb_flags,
     unsigned int sb_flags_mask)
{
return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
    sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
}
EXPORT_SYMBOL(fs_context_for_reconfigure);

/**
* fs_context_for_submount: allocate a new fs_context for a submount
* @type: file_system_type of the new context
* @reference: reference dentry from which to copy relevant info
*
* Allocate a new fs_context suitable for a submount. This also ensures that
* the fc->security object is inherited from @reference (if needed).
*/
struct fs_context *fs_context_for_submount(struct file_system_type *type,
        struct dentry *reference)
{
struct fs_context *fc;
int ret;

fc = alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
if (IS_ERR(fc))
  return fc;

ret = security_fs_context_submount(fc, reference->d_sb);
if (ret) {
  put_fs_context(fc);
  return ERR_PTR(ret);
}

return fc;
}
EXPORT_SYMBOL(fs_context_for_submount);

void fc_drop_locked(struct fs_context *fc)
{
struct super_block *sb = fc->root->d_sb;
dput(fc->root);
fc->root = NULL;
deactivate_locked_super(sb);
}

static void legacy_fs_context_free(struct fs_context *fc);

/**
* vfs_dup_fs_context - Duplicate a filesystem context.
* @src_fc: The context to copy.
*/
struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
{
struct fs_context *fc;
int ret;

if (!src_fc->ops->dup)
  return ERR_PTR(-EOPNOTSUPP);

fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
if (!fc)
  return ERR_PTR(-ENOMEM);

mutex_init(&fc->uapi_mutex);

fc->fs_private = NULL;
fc->s_fs_info = NULL;
fc->source = NULL;
fc->security = NULL;
get_filesystem(fc->fs_type);
get_net(fc->net_ns);
get_user_ns(fc->user_ns);
get_cred(fc->cred);
if (fc->log.log)
  refcount_inc(&fc->log.log->usage);

/* Can't call put until we've called ->dup */
ret = fc->ops->dup(fc, src_fc);
if (ret < 0)
  goto err_fc;

ret = security_fs_context_dup(fc, src_fc);
if (ret < 0)
  goto err_fc;
return fc;

err_fc:
put_fs_context(fc);
return ERR_PTR(ret);
}
EXPORT_SYMBOL(vfs_dup_fs_context);

/**
* logfc - Log a message to a filesystem context
* @log: The filesystem context to log to, or NULL to use printk.
* @prefix: A string to prefix the output with, or NULL.
* @level: 'w' for a warning, 'e' for an error.  Anything else is a notice.
* @fmt: The format of the buffer.
*/
void logfc(struct fc_log *log, const char *prefix, char level, const char *fmt, ...)
{
va_list va;
struct va_format vaf = {.fmt = fmt, .va = &va};

va_start(va, fmt);
if (!log) {
  switch (level) {
  case 'w':
   printk(KERN_WARNING "%s%s%pV\n", prefix ? prefix : "",
      prefix ? ": " : "", &vaf);
   break;
  case 'e':
   printk(KERN_ERR "%s%s%pV\n", prefix ? prefix : "",
      prefix ? ": " : "", &vaf);
   break;
  case 'i':
   printk(KERN_INFO "%s%s%pV\n", prefix ? prefix : "",
      prefix ? ": " : "", &vaf);
   break;
  default:
   printk(KERN_NOTICE "%s%s%pV\n", prefix ? prefix : "",
      prefix ? ": " : "", &vaf);
   break;
  }
} else {
  unsigned int logsize = ARRAY_SIZE(log->buffer);
  u8 index;
  char *q = kasprintf(GFP_KERNEL, "%c %s%s%pV\n", level,
      prefix ? prefix : "",
      prefix ? ": " : "", &vaf);

  index = log->head & (logsize - 1);
  BUILD_BUG_ON(sizeof(log->head) != sizeof(u8) ||
        sizeof(log->tail) != sizeof(u8));
  if ((u8)(log->head - log->tail) == logsize) {
   /* The buffer is full, discard the oldest message */
   if (log->need_free & (1 << index))
    kfree(log->buffer[index]);
   log->tail++;
  }

  log->buffer[index] = q ? q : "OOM: Can't store error string";
  if (q)
   log->need_free |= 1 << index;
  else
   log->need_free &= ~(1 << index);
  log->head++;
}
va_end(va);
}
EXPORT_SYMBOL(logfc);

/*
* Free a logging structure.
*/
static void put_fc_log(struct fs_context *fc)
{
struct fc_log *log = fc->log.log;
int i;

if (log) {
  if (refcount_dec_and_test(&log->usage)) {
   fc->log.log = NULL;
   for (i = 0; i < ARRAY_SIZE(log->buffer) ; i++)
    if (log->need_free & (1 << i))
     kfree(log->buffer[i]);
   kfree(log);
  }
}
}

/**
* put_fs_context - Dispose of a superblock configuration context.
* @fc: The context to dispose of.
*/
void put_fs_context(struct fs_context *fc)
{
struct super_block *sb;

if (fc->root) {
  sb = fc->root->d_sb;
  dput(fc->root);
  fc->root = NULL;
  deactivate_super(sb);
}

if (fc->need_free && fc->ops && fc->ops->free)
  fc->ops->free(fc);

security_free_mnt_opts(&fc->security);
put_net(fc->net_ns);
put_user_ns(fc->user_ns);
put_cred(fc->cred);
put_fc_log(fc);
put_filesystem(fc->fs_type);
kfree(fc->source);
kfree(fc);
}
EXPORT_SYMBOL(put_fs_context);

/*
* Free the config for a filesystem that doesn't support fs_context.
*/
static void legacy_fs_context_free(struct fs_context *fc)
{
struct legacy_fs_context *ctx = fc->fs_private;

if (ctx) {
  if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS)
   kfree(ctx->legacy_data);
  kfree(ctx);
}
}

/*
* Duplicate a legacy config.
*/
static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
{
struct legacy_fs_context *ctx;
struct legacy_fs_context *src_ctx = src_fc->fs_private;

ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
if (!ctx)
  return -ENOMEM;

if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
  ctx->legacy_data = kmemdup(src_ctx->legacy_data,
        src_ctx->data_size, GFP_KERNEL);
  if (!ctx->legacy_data) {
   kfree(ctx);
   return -ENOMEM;
  }
}

fc->fs_private = ctx;
return 0;
}

/*
* Add a parameter to a legacy config.  We build up a comma-separated list of
* options.
*/
static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
struct legacy_fs_context *ctx = fc->fs_private;
unsigned int size = ctx->data_size;
size_t len = 0;
int ret;

ret = vfs_parse_fs_param_source(fc, param);
if (ret != -ENOPARAM)
  return ret;

if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
  return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");

switch (param->type) {
case fs_value_is_string:
  len = 1 + param->size;
  fallthrough;
case fs_value_is_flag:
  len += strlen(param->key);
  break;
default:
  return invalf(fc, "VFS: Legacy: Parameter type for '%s' not supported",
         param->key);
}

if (size + len + 2 > PAGE_SIZE)
  return invalf(fc, "VFS: Legacy: Cumulative options too large");
if (strchr(param->key, ',') ||
     (param->type == fs_value_is_string &&
      memchr(param->string, ',', param->size)))
  return invalf(fc, "VFS: Legacy: Option '%s' contained comma",
         param->key);
if (!ctx->legacy_data) {
  ctx->legacy_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
  if (!ctx->legacy_data)
   return -ENOMEM;
}

if (size)
  ctx->legacy_data[size++] = ',';
len = strlen(param->key);
memcpy(ctx->legacy_data + size, param->key, len);
size += len;
if (param->type == fs_value_is_string) {
  ctx->legacy_data[size++] = '=';
  memcpy(ctx->legacy_data + size, param->string, param->size);
  size += param->size;
}
ctx->legacy_data[size] = '\0';
ctx->data_size = size;
ctx->param_type = LEGACY_FS_INDIVIDUAL_PARAMS;
return 0;
}

/*
* Add monolithic mount data.
*/
static int legacy_parse_monolithic(struct fs_context *fc, void *data)
{
struct legacy_fs_context *ctx = fc->fs_private;

if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
  pr_warn("VFS: Can't mix monolithic and individual options\n");
  return -EINVAL;
}

ctx->legacy_data = data;
ctx->param_type = LEGACY_FS_MONOLITHIC_PARAMS;
if (!ctx->legacy_data)
  return 0;

if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
  return 0;
return security_sb_eat_lsm_opts(ctx->legacy_data, &fc->security);
}

/*
* Get a mountable root with the legacy mount command.
*/
static int legacy_get_tree(struct fs_context *fc)
{
struct legacy_fs_context *ctx = fc->fs_private;
struct super_block *sb;
struct dentry *root;

root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
          fc->source, ctx->legacy_data);
if (IS_ERR(root))
  return PTR_ERR(root);

sb = root->d_sb;
BUG_ON(!sb);

fc->root = root;
return 0;
}

/*
* Handle remount.
*/
static int legacy_reconfigure(struct fs_context *fc)
{
struct legacy_fs_context *ctx = fc->fs_private;
struct super_block *sb = fc->root->d_sb;

if (!sb->s_op->remount_fs)
  return 0;

return sb->s_op->remount_fs(sb, &fc->sb_flags,
        ctx ? ctx->legacy_data : NULL);
}

const struct fs_context_operations legacy_fs_context_ops = {
.free   = legacy_fs_context_free,
.dup   = legacy_fs_context_dup,
.parse_param  = legacy_parse_param,
.parse_monolithic = legacy_parse_monolithic,
.get_tree  = legacy_get_tree,
.reconfigure  = legacy_reconfigure,
};

/*
* Initialise a legacy context for a filesystem that doesn't support
* fs_context.
*/
static int legacy_init_fs_context(struct fs_context *fc)
{
fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL_ACCOUNT);
if (!fc->fs_private)
  return -ENOMEM;
fc->ops = &legacy_fs_context_ops;
return 0;
}

int parse_monolithic_mount_data(struct fs_context *fc, void *data)
{
int (*monolithic_mount_data)(struct fs_context *, void *);

monolithic_mount_data = fc->ops->parse_monolithic;
if (!monolithic_mount_data)
  monolithic_mount_data = generic_parse_monolithic;

return monolithic_mount_data(fc, data);
}

/*
* Clean up a context after performing an action on it and put it into a state
* from where it can be used to reconfigure a superblock.
*
* Note that here we do only the parts that can't fail; the rest is in
* finish_clean_context() below and in between those fs_context is marked
* FS_CONTEXT_AWAITING_RECONF.  The reason for splitup is that after
* successful mount or remount we need to report success to userland.
* Trying to do full reinit (for the sake of possible subsequent remount)
* and failing to allocate memory would've put us into a nasty situation.
* So here we only discard the old state and reinitialization is left
* until we actually try to reconfigure.
*/
void vfs_clean_context(struct fs_context *fc)
{
if (fc->need_free && fc->ops && fc->ops->free)
  fc->ops->free(fc);
fc->need_free = false;
fc->fs_private = NULL;
fc->s_fs_info = NULL;
fc->sb_flags = 0;
security_free_mnt_opts(&fc->security);
kfree(fc->source);
fc->source = NULL;
fc->exclusive = false;

fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
fc->phase = FS_CONTEXT_AWAITING_RECONF;
}

int finish_clean_context(struct fs_context *fc)
{
int error;

if (fc->phase != FS_CONTEXT_AWAITING_RECONF)
  return 0;

if (fc->fs_type->init_fs_context)
  error = fc->fs_type->init_fs_context(fc);
else
  error = legacy_init_fs_context(fc);
if (unlikely(error)) {
  fc->phase = FS_CONTEXT_FAILED;
  return error;
}
fc->need_free = true;
fc->phase = FS_CONTEXT_RECONF_PARAMS;
return 0;
}

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