linux/fs/ubifs/xattr.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём)
 *          Adrian Hunter
 */

/*
 * This file implements UBIFS extended attributes support.
 *
 * Extended attributes are implemented as regular inodes with attached data,
 * which limits extended attribute size to UBIFS block size (4KiB). Names of
 * extended attributes are described by extended attribute entries (xentries),
 * which are almost identical to directory entries, but have different key type.
 *
 * In other words, the situation with extended attributes is very similar to
 * directories. Indeed, any inode (but of course not xattr inodes) may have a
 * number of associated xentries, just like directory inodes have associated
 * directory entries. Extended attribute entries store the name of the extended
 * attribute, the host inode number, and the extended attribute inode number.
 * Similarly, direntries store the name, the parent and the target inode
 * numbers. Thus, most of the common UBIFS mechanisms may be re-used for
 * extended attributes.
 *
 * The number of extended attributes is not limited, but there is Linux
 * limitation on the maximum possible size of the list of all extended
 * attributes associated with an inode (%XATTR_LIST_MAX), so UBIFS makes sure
 * the sum of all extended attribute names of the inode does not exceed that
 * limit.
 *
 * Extended attributes are synchronous, which means they are written to the
 * flash media synchronously and there is no write-back for extended attribute
 * inodes. The extended attribute values are not stored in compressed form on
 * the media.
 *
 * Since extended attributes are represented by regular inodes, they are cached
 * in the VFS inode cache. The xentries are cached in the LNC cache (see
 * tnc.c).
 *
 * ACL support is not implemented.
 */

#include "ubifs.h"
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/xattr.h>

/*
 * Extended attribute type constants.
 *
 * USER_XATTR: user extended attribute ("user.*")
 * TRUSTED_XATTR: trusted extended attribute ("trusted.*)
 * SECURITY_XATTR: security extended attribute ("security.*")
 */
enum { … };

static const struct inode_operations empty_iops;
static const struct file_operations empty_fops;

/**
 * create_xattr - create an extended attribute.
 * @c: UBIFS file-system description object
 * @host: host inode
 * @nm: extended attribute name
 * @value: extended attribute value
 * @size: size of extended attribute value
 *
 * This is a helper function which creates an extended attribute of name @nm
 * and value @value for inode @host. The host inode is also updated on flash
 * because the ctime and extended attribute accounting data changes. This
 * function returns zero in case of success and a negative error code in case
 * of failure.
 */
static int create_xattr(struct ubifs_info *c, struct inode *host,
			const struct fscrypt_name *nm, const void *value, int size)
{ … }

/**
 * change_xattr - change an extended attribute.
 * @c: UBIFS file-system description object
 * @host: host inode
 * @inode: extended attribute inode
 * @value: extended attribute value
 * @size: size of extended attribute value
 *
 * This helper function changes the value of extended attribute @inode with new
 * data from @value. Returns zero in case of success and a negative error code
 * in case of failure.
 */
static int change_xattr(struct ubifs_info *c, struct inode *host,
			struct inode *inode, const void *value, int size)
{ … }

static struct inode *iget_xattr(struct ubifs_info *c, ino_t inum)
{ … }

int ubifs_xattr_set(struct inode *host, const char *name, const void *value,
		    size_t size, int flags, bool check_lock)
{ … }

ssize_t ubifs_xattr_get(struct inode *host, const char *name, void *buf,
			size_t size)
{ … }

static bool xattr_visible(const char *name)
{ … }

ssize_t ubifs_listxattr(struct dentry *dentry, char *buffer, size_t size)
{ … }

static int remove_xattr(struct ubifs_info *c, struct inode *host,
			struct inode *inode, const struct fscrypt_name *nm)
{ … }

int ubifs_purge_xattrs(struct inode *host)
{ … }

/**
 * ubifs_evict_xattr_inode - Evict an xattr inode.
 * @c: UBIFS file-system description object
 * @xattr_inum: xattr inode number
 *
 * When an inode that hosts xattrs is being removed we have to make sure
 * that cached inodes of the xattrs also get removed from the inode cache
 * otherwise we'd waste memory. This function looks up an inode from the
 * inode cache and clears the link counter such that iput() will evict
 * the inode.
 */
void ubifs_evict_xattr_inode(struct ubifs_info *c, ino_t xattr_inum)
{ … }

static int ubifs_xattr_remove(struct inode *host, const char *name)
{ … }

#ifdef CONFIG_UBIFS_FS_SECURITY
static int init_xattrs(struct inode *inode, const struct xattr *xattr_array,
		      void *fs_info)
{ … }

int ubifs_init_security(struct inode *dentry, struct inode *inode,
			const struct qstr *qstr)
{ … }
#endif

static int xattr_get(const struct xattr_handler *handler,
			   struct dentry *dentry, struct inode *inode,
			   const char *name, void *buffer, size_t size)
{ … }

static int xattr_set(const struct xattr_handler *handler,
			   struct mnt_idmap *idmap,
			   struct dentry *dentry, struct inode *inode,
			   const char *name, const void *value,
			   size_t size, int flags)
{ … }

static const struct xattr_handler ubifs_user_xattr_handler = …;

static const struct xattr_handler ubifs_trusted_xattr_handler = …;

#ifdef CONFIG_UBIFS_FS_SECURITY
static const struct xattr_handler ubifs_security_xattr_handler = …;
#endif

const struct xattr_handler * const ubifs_xattr_handlers[] = …;