linux/fs/ext2/xattr.c

// SPDX-License-Identifier: GPL-2.0
/*
 * linux/fs/ext2/xattr.c
 *
 * Copyright (C) 2001-2003 Andreas Gruenbacher <[email protected]>
 *
 * Fix by Harrison Xing <[email protected]>.
 * Extended attributes for symlinks and special files added per
 *  suggestion of Luka Renko <[email protected]>.
 * xattr consolidation Copyright (c) 2004 James Morris <[email protected]>,
 *  Red Hat Inc.
 *
 */

/*
 * Extended attributes are stored on disk blocks allocated outside of
 * any inode. The i_file_acl field is then made to point to this allocated
 * block. If all extended attributes of an inode are identical, these
 * inodes may share the same extended attribute block. Such situations
 * are automatically detected by keeping a cache of recent attribute block
 * numbers and hashes over the block's contents in memory.
 *
 *
 * Extended attribute block layout:
 *
 *   +------------------+
 *   | header           |
 *   | entry 1          | |
 *   | entry 2          | | growing downwards
 *   | entry 3          | v
 *   | four null bytes  |
 *   | . . .            |
 *   | value 1          | ^
 *   | value 3          | | growing upwards
 *   | value 2          | |
 *   +------------------+
 *
 * The block header is followed by multiple entry descriptors. These entry
 * descriptors are variable in size, and aligned to EXT2_XATTR_PAD
 * byte boundaries. The entry descriptors are sorted by attribute name,
 * so that two extended attribute blocks can be compared efficiently.
 *
 * Attribute values are aligned to the end of the block, stored in
 * no specific order. They are also padded to EXT2_XATTR_PAD byte
 * boundaries. No additional gaps are left between them.
 *
 * Locking strategy
 * ----------------
 * EXT2_I(inode)->i_file_acl is protected by EXT2_I(inode)->xattr_sem.
 * EA blocks are only changed if they are exclusive to an inode, so
 * holding xattr_sem also means that nothing but the EA block's reference
 * count will change. Multiple writers to an EA block are synchronized
 * by the bh lock. No more than a single bh lock is held at any time
 * to avoid deadlocks.
 */

#include <linux/buffer_head.h>
#include <linux/init.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/mbcache.h>
#include <linux/quotaops.h>
#include <linux/rwsem.h>
#include <linux/security.h>
#include "ext2.h"
#include "xattr.h"
#include "acl.h"

#define HDR(bh) …
#define ENTRY(ptr) …
#define FIRST_ENTRY(bh) …
#define IS_LAST_ENTRY(entry) …

#ifdef EXT2_XATTR_DEBUG
#define ea_idebug …
#define ea_bdebug …
#else
#define ea_idebug(inode, f...) …
#define ea_bdebug(bh, f...) …
#endif

static int ext2_xattr_set2(struct inode *, struct buffer_head *,
			   struct ext2_xattr_header *);

static int ext2_xattr_cache_insert(struct mb_cache *, struct buffer_head *);
static struct buffer_head *ext2_xattr_cache_find(struct inode *,
						 struct ext2_xattr_header *);
static void ext2_xattr_rehash(struct ext2_xattr_header *,
			      struct ext2_xattr_entry *);

static const struct xattr_handler * const ext2_xattr_handler_map[] = …;

const struct xattr_handler * const ext2_xattr_handlers[] = …;

#define EA_BLOCK_CACHE(inode) …

static inline const char *ext2_xattr_prefix(int name_index,
					    struct dentry *dentry)
{ … }

static bool
ext2_xattr_header_valid(struct ext2_xattr_header *header)
{ … }

static bool
ext2_xattr_entry_valid(struct ext2_xattr_entry *entry,
		       char *end, size_t end_offs)
{ … }

static int
ext2_xattr_cmp_entry(int name_index, size_t name_len, const char *name,
		     struct ext2_xattr_entry *entry)
{ … }

/*
 * ext2_xattr_get()
 *
 * Copy an extended attribute into the buffer
 * provided, or compute the buffer size required.
 * Buffer is NULL to compute the size of the buffer required.
 *
 * Returns a negative error number on failure, or the number of bytes
 * used / required on success.
 */
int
ext2_xattr_get(struct inode *inode, int name_index, const char *name,
	       void *buffer, size_t buffer_size)
{ … }

/*
 * ext2_xattr_list()
 *
 * Copy a list of attribute names into the buffer
 * provided, or compute the buffer size required.
 * Buffer is NULL to compute the size of the buffer required.
 *
 * Returns a negative error number on failure, or the number of bytes
 * used / required on success.
 */
static int
ext2_xattr_list(struct dentry *dentry, char *buffer, size_t buffer_size)
{ … }

/*
 * Inode operation listxattr()
 *
 * d_inode(dentry)->i_mutex: don't care
 */
ssize_t
ext2_listxattr(struct dentry *dentry, char *buffer, size_t size)
{ … }

/*
 * If the EXT2_FEATURE_COMPAT_EXT_ATTR feature of this file system is
 * not set, set it.
 */
static void ext2_xattr_update_super_block(struct super_block *sb)
{ … }

/*
 * ext2_xattr_set()
 *
 * Create, replace or remove an extended attribute for this inode.  Value
 * is NULL to remove an existing extended attribute, and non-NULL to
 * either replace an existing extended attribute, or create a new extended
 * attribute. The flags XATTR_REPLACE and XATTR_CREATE
 * specify that an extended attribute must exist and must not exist
 * previous to the call, respectively.
 *
 * Returns 0, or a negative error number on failure.
 */
int
ext2_xattr_set(struct inode *inode, int name_index, const char *name,
	       const void *value, size_t value_len, int flags)
{ … }

static void ext2_xattr_release_block(struct inode *inode,
				     struct buffer_head *bh)
{ … }

/*
 * Second half of ext2_xattr_set(): Update the file system.
 */
static int
ext2_xattr_set2(struct inode *inode, struct buffer_head *old_bh,
		struct ext2_xattr_header *header)
{ … }

/*
 * ext2_xattr_delete_inode()
 *
 * Free extended attribute resources associated with this inode. This
 * is called immediately before an inode is freed.
 */
void
ext2_xattr_delete_inode(struct inode *inode)
{ … }

/*
 * ext2_xattr_cache_insert()
 *
 * Create a new entry in the extended attribute cache, and insert
 * it unless such an entry is already in the cache.
 *
 * Returns 0, or a negative error number on failure.
 */
static int
ext2_xattr_cache_insert(struct mb_cache *cache, struct buffer_head *bh)
{ … }

/*
 * ext2_xattr_cmp()
 *
 * Compare two extended attribute blocks for equality.
 *
 * Returns 0 if the blocks are equal, 1 if they differ, and
 * a negative error number on errors.
 */
static int
ext2_xattr_cmp(struct ext2_xattr_header *header1,
	       struct ext2_xattr_header *header2)
{ … }

/*
 * ext2_xattr_cache_find()
 *
 * Find an identical extended attribute block.
 *
 * Returns a locked buffer head to the block found, or NULL if such
 * a block was not found or an error occurred.
 */
static struct buffer_head *
ext2_xattr_cache_find(struct inode *inode, struct ext2_xattr_header *header)
{ … }

#define NAME_HASH_SHIFT …
#define VALUE_HASH_SHIFT …

/*
 * ext2_xattr_hash_entry()
 *
 * Compute the hash of an extended attribute.
 */
static inline void ext2_xattr_hash_entry(struct ext2_xattr_header *header,
					 struct ext2_xattr_entry *entry)
{ … }

#undef NAME_HASH_SHIFT
#undef VALUE_HASH_SHIFT

#define BLOCK_HASH_SHIFT …

/*
 * ext2_xattr_rehash()
 *
 * Re-compute the extended attribute hash value after an entry has changed.
 */
static void ext2_xattr_rehash(struct ext2_xattr_header *header,
			      struct ext2_xattr_entry *entry)
{ … }

#undef BLOCK_HASH_SHIFT

#define HASH_BUCKET_BITS …

struct mb_cache *ext2_xattr_create_cache(void)
{ … }

void ext2_xattr_destroy_cache(struct mb_cache *cache)
{ … }