xattr.c

Go to the documentation of this file.

/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * 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>
#include <linux/posix_acl_xattr.h>

/*
 * Limit the number of extended attributes per inode so that the total size
 * (@xattr_size) is guaranteeded to fit in an 'unsigned int'.
 */
#define MAX_XATTRS_PER_INODE 65535

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

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

static int create_xattr(struct ubifs_info *c, struct inode *host,
            const struct qstr *nm, const void *value, int size)
{
    int err;
    struct inode *inode;
    struct ubifs_inode *ui, *host_ui = ubifs_inode(host);
    struct ubifs_budget_req req = { .new_ino = 1, .new_dent = 1,
                .new_ino_d = ALIGN(size, 8), .dirtied_ino = 1,
                .dirtied_ino_d = ALIGN(host_ui->data_len, 8) };

    if (host_ui->xattr_cnt >= MAX_XATTRS_PER_INODE)
        return -ENOSPC;
    /*
     * Linux limits the maximum size of the extended attribute names list
     * to %XATTR_LIST_MAX. This means we should not allow creating more
     * extended attributes if the name list becomes larger. This limitation
     * is artificial for UBIFS, though.
     */
    if (host_ui->xattr_names + host_ui->xattr_cnt +
                    nm->len + 1 > XATTR_LIST_MAX)
        return -ENOSPC;

    err = ubifs_budget_space(c, &req);
    if (err)
        return err;

    inode = ubifs_new_inode(c, host, S_IFREG | S_IRWXUGO);
    if (IS_ERR(inode)) {
        err = PTR_ERR(inode);
        goto out_budg;
    }

    /* Re-define all operations to be "nothing" */
    inode->i_mapping->a_ops = &empty_aops;
    inode->i_op = &empty_iops;
    inode->i_fop = &empty_fops;

    inode->i_flags |= S_SYNC | S_NOATIME | S_NOCMTIME | S_NOQUOTA;
    ui = ubifs_inode(inode);
    ui->xattr = 1;
    ui->flags |= UBIFS_XATTR_FL;
    ui->data = kmemdup(value, size, GFP_NOFS);
    if (!ui->data) {
        err = -ENOMEM;
        goto out_free;
    }
    inode->i_size = ui->ui_size = size;
    ui->data_len = size;

    mutex_lock(&host_ui->ui_mutex);
    host->i_ctime = ubifs_current_time(host);
    host_ui->xattr_cnt += 1;
    host_ui->xattr_size += CALC_DENT_SIZE(nm->len);
    host_ui->xattr_size += CALC_XATTR_BYTES(size);
    host_ui->xattr_names += nm->len;

    err = ubifs_jnl_update(c, host, nm, inode, 0, 1);
    if (err)
        goto out_cancel;
    mutex_unlock(&host_ui->ui_mutex);

    ubifs_release_budget(c, &req);
    insert_inode_hash(inode);
    iput(inode);
    return 0;

out_cancel:
    host_ui->xattr_cnt -= 1;
    host_ui->xattr_size -= CALC_DENT_SIZE(nm->len);
    host_ui->xattr_size -= CALC_XATTR_BYTES(size);
    mutex_unlock(&host_ui->ui_mutex);
out_free:
    make_bad_inode(inode);
    iput(inode);
out_budg:
    ubifs_release_budget(c, &req);
    return err;
}

static int change_xattr(struct ubifs_info *c, struct inode *host,
            struct inode *inode, const void *value, int size)
{
    int err;
    struct ubifs_inode *host_ui = ubifs_inode(host);
    struct ubifs_inode *ui = ubifs_inode(inode);
    struct ubifs_budget_req req = { .dirtied_ino = 2,
        .dirtied_ino_d = ALIGN(size, 8) + ALIGN(host_ui->data_len, 8) };

    ubifs_assert(ui->data_len == inode->i_size);
    err = ubifs_budget_space(c, &req);
    if (err)
        return err;

    kfree(ui->data);
    ui->data = kmemdup(value, size, GFP_NOFS);
    if (!ui->data) {
        err = -ENOMEM;
        goto out_free;
    }
    inode->i_size = ui->ui_size = size;
    ui->data_len = size;

    mutex_lock(&host_ui->ui_mutex);
    host->i_ctime = ubifs_current_time(host);
    host_ui->xattr_size -= CALC_XATTR_BYTES(ui->data_len);
    host_ui->xattr_size += CALC_XATTR_BYTES(size);

    /*
     * It is important to write the host inode after the xattr inode
     * because if the host inode gets synchronized (via 'fsync()'), then
     * the extended attribute inode gets synchronized, because it goes
     * before the host inode in the write-buffer.
     */
    err = ubifs_jnl_change_xattr(c, inode, host);
    if (err)
        goto out_cancel;
    mutex_unlock(&host_ui->ui_mutex);

    ubifs_release_budget(c, &req);
    return 0;

out_cancel:
    host_ui->xattr_size -= CALC_XATTR_BYTES(size);
    host_ui->xattr_size += CALC_XATTR_BYTES(ui->data_len);
    mutex_unlock(&host_ui->ui_mutex);
    make_bad_inode(inode);
out_free:
    ubifs_release_budget(c, &req);
    return err;
}

static int check_namespace(const struct qstr *nm)
{
    int type;

    if (nm->len > UBIFS_MAX_NLEN)
        return -ENAMETOOLONG;

    if (!strncmp(nm->name, XATTR_TRUSTED_PREFIX,
             XATTR_TRUSTED_PREFIX_LEN)) {
        if (nm->name[sizeof(XATTR_TRUSTED_PREFIX) - 1] == '\0')
            return -EINVAL;
        type = TRUSTED_XATTR;
    } else if (!strncmp(nm->name, XATTR_USER_PREFIX,
                      XATTR_USER_PREFIX_LEN)) {
        if (nm->name[XATTR_USER_PREFIX_LEN] == '\0')
            return -EINVAL;
        type = USER_XATTR;
    } else if (!strncmp(nm->name, XATTR_SECURITY_PREFIX,
                     XATTR_SECURITY_PREFIX_LEN)) {
        if (nm->name[sizeof(XATTR_SECURITY_PREFIX) - 1] == '\0')
            return -EINVAL;
        type = SECURITY_XATTR;
    } else
        return -EOPNOTSUPP;

    return type;
}

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

    inode = ubifs_iget(c->vfs_sb, inum);
    if (IS_ERR(inode)) {
        ubifs_err("dead extended attribute entry, error %d",
              (int)PTR_ERR(inode));
        return inode;
    }
    if (ubifs_inode(inode)->xattr)
        return inode;
    ubifs_err("corrupt extended attribute entry");
    iput(inode);
    return ERR_PTR(-EINVAL);
}

int ubifs_setxattr(struct dentry *dentry, const char *name,
           const void *value, size_t size, int flags)
{
    struct inode *inode, *host = dentry->d_inode;
    struct ubifs_info *c = host->i_sb->s_fs_info;
    struct qstr nm = QSTR_INIT(name, strlen(name));
    struct ubifs_dent_node *xent;
    union ubifs_key key;
    int err, type;

    dbg_gen("xattr '%s', host ino %lu ('%.*s'), size %zd", name,
        host->i_ino, dentry->d_name.len, dentry->d_name.name, size);
    ubifs_assert(mutex_is_locked(&host->i_mutex));

    if (size > UBIFS_MAX_INO_DATA)
        return -ERANGE;

    type = check_namespace(&nm);
    if (type < 0)
        return type;

    xent = kmalloc(UBIFS_MAX_XENT_NODE_SZ, GFP_NOFS);
    if (!xent)
        return -ENOMEM;

    /*
     * The extended attribute entries are stored in LNC, so multiple
     * look-ups do not involve reading the flash.
     */
    xent_key_init(c, &key, host->i_ino, &nm);
    err = ubifs_tnc_lookup_nm(c, &key, xent, &nm);
    if (err) {
        if (err != -ENOENT)
            goto out_free;

        if (flags & XATTR_REPLACE)
            /* We are asked not to create the xattr */
            err = -ENODATA;
        else
            err = create_xattr(c, host, &nm, value, size);
        goto out_free;
    }

    if (flags & XATTR_CREATE) {
        /* We are asked not to replace the xattr */
        err = -EEXIST;
        goto out_free;
    }

    inode = iget_xattr(c, le64_to_cpu(xent->inum));
    if (IS_ERR(inode)) {
        err = PTR_ERR(inode);
        goto out_free;
    }

    err = change_xattr(c, host, inode, value, size);
    iput(inode);

out_free:
    kfree(xent);
    return err;
}

ssize_t ubifs_getxattr(struct dentry *dentry, const char *name, void *buf,
               size_t size)
{
    struct inode *inode, *host = dentry->d_inode;
    struct ubifs_info *c = host->i_sb->s_fs_info;
    struct qstr nm = QSTR_INIT(name, strlen(name));
    struct ubifs_inode *ui;
    struct ubifs_dent_node *xent;
    union ubifs_key key;
    int err;

    dbg_gen("xattr '%s', ino %lu ('%.*s'), buf size %zd", name,
        host->i_ino, dentry->d_name.len, dentry->d_name.name, size);

    err = check_namespace(&nm);
    if (err < 0)
        return err;

    xent = kmalloc(UBIFS_MAX_XENT_NODE_SZ, GFP_NOFS);
    if (!xent)
        return -ENOMEM;

    xent_key_init(c, &key, host->i_ino, &nm);
    err = ubifs_tnc_lookup_nm(c, &key, xent, &nm);
    if (err) {
        if (err == -ENOENT)
            err = -ENODATA;
        goto out_unlock;
    }

    inode = iget_xattr(c, le64_to_cpu(xent->inum));
    if (IS_ERR(inode)) {
        err = PTR_ERR(inode);
        goto out_unlock;
    }

    ui = ubifs_inode(inode);
    ubifs_assert(inode->i_size == ui->data_len);
    ubifs_assert(ubifs_inode(host)->xattr_size > ui->data_len);

    if (buf) {
        /* If @buf is %NULL we are supposed to return the length */
        if (ui->data_len > size) {
            ubifs_err("buffer size %zd, xattr len %d",
                  size, ui->data_len);
            err = -ERANGE;
            goto out_iput;
        }

        memcpy(buf, ui->data, ui->data_len);
    }
    err = ui->data_len;

out_iput:
    iput(inode);
out_unlock:
    kfree(xent);
    return err;
}

ssize_t ubifs_listxattr(struct dentry *dentry, char *buffer, size_t size)
{
    union ubifs_key key;
    struct inode *host = dentry->d_inode;
    struct ubifs_info *c = host->i_sb->s_fs_info;
    struct ubifs_inode *host_ui = ubifs_inode(host);
    struct ubifs_dent_node *xent, *pxent = NULL;
    int err, len, written = 0;
    struct qstr nm = { .name = NULL };

    dbg_gen("ino %lu ('%.*s'), buffer size %zd", host->i_ino,
        dentry->d_name.len, dentry->d_name.name, size);

    len = host_ui->xattr_names + host_ui->xattr_cnt;
    if (!buffer)
        /*
         * We should return the minimum buffer size which will fit a
         * null-terminated list of all the extended attribute names.
         */
        return len;

    if (len > size)
        return -ERANGE;

    lowest_xent_key(c, &key, host->i_ino);
    while (1) {
        int type;

        xent = ubifs_tnc_next_ent(c, &key, &nm);
        if (IS_ERR(xent)) {
            err = PTR_ERR(xent);
            break;
        }

        nm.name = xent->name;
        nm.len = le16_to_cpu(xent->nlen);

        type = check_namespace(&nm);
        if (unlikely(type < 0)) {
            err = type;
            break;
        }

        /* Show trusted namespace only for "power" users */
        if (type != TRUSTED_XATTR || capable(CAP_SYS_ADMIN)) {
            memcpy(buffer + written, nm.name, nm.len + 1);
            written += nm.len + 1;
        }

        kfree(pxent);
        pxent = xent;
        key_read(c, &xent->key, &key);
    }

    kfree(pxent);
    if (err != -ENOENT) {
        ubifs_err("cannot find next direntry, error %d", err);
        return err;
    }

    ubifs_assert(written <= size);
    return written;
}

static int remove_xattr(struct ubifs_info *c, struct inode *host,
            struct inode *inode, const struct qstr *nm)
{
    int err;
    struct ubifs_inode *host_ui = ubifs_inode(host);
    struct ubifs_inode *ui = ubifs_inode(inode);
    struct ubifs_budget_req req = { .dirtied_ino = 2, .mod_dent = 1,
                .dirtied_ino_d = ALIGN(host_ui->data_len, 8) };

    ubifs_assert(ui->data_len == inode->i_size);

    err = ubifs_budget_space(c, &req);
    if (err)
        return err;

    mutex_lock(&host_ui->ui_mutex);
    host->i_ctime = ubifs_current_time(host);
    host_ui->xattr_cnt -= 1;
    host_ui->xattr_size -= CALC_DENT_SIZE(nm->len);
    host_ui->xattr_size -= CALC_XATTR_BYTES(ui->data_len);
    host_ui->xattr_names -= nm->len;

    err = ubifs_jnl_delete_xattr(c, host, inode, nm);
    if (err)
        goto out_cancel;
    mutex_unlock(&host_ui->ui_mutex);

    ubifs_release_budget(c, &req);
    return 0;

out_cancel:
    host_ui->xattr_cnt += 1;
    host_ui->xattr_size += CALC_DENT_SIZE(nm->len);
    host_ui->xattr_size += CALC_XATTR_BYTES(ui->data_len);
    mutex_unlock(&host_ui->ui_mutex);
    ubifs_release_budget(c, &req);
    make_bad_inode(inode);
    return err;
}

int ubifs_removexattr(struct dentry *dentry, const char *name)
{
    struct inode *inode, *host = dentry->d_inode;
    struct ubifs_info *c = host->i_sb->s_fs_info;
    struct qstr nm = QSTR_INIT(name, strlen(name));
    struct ubifs_dent_node *xent;
    union ubifs_key key;
    int err;

    dbg_gen("xattr '%s', ino %lu ('%.*s')", name,
        host->i_ino, dentry->d_name.len, dentry->d_name.name);
    ubifs_assert(mutex_is_locked(&host->i_mutex));

    err = check_namespace(&nm);
    if (err < 0)
        return err;

    xent = kmalloc(UBIFS_MAX_XENT_NODE_SZ, GFP_NOFS);
    if (!xent)
        return -ENOMEM;

    xent_key_init(c, &key, host->i_ino, &nm);
    err = ubifs_tnc_lookup_nm(c, &key, xent, &nm);
    if (err) {
        if (err == -ENOENT)
            err = -ENODATA;
        goto out_free;
    }

    inode = iget_xattr(c, le64_to_cpu(xent->inum));
    if (IS_ERR(inode)) {
        err = PTR_ERR(inode);
        goto out_free;
    }

    ubifs_assert(inode->i_nlink == 1);
    clear_nlink(inode);
    err = remove_xattr(c, host, inode, &nm);
    if (err)
        set_nlink(inode, 1);

    /* If @i_nlink is 0, 'iput()' will delete the inode */
    iput(inode);

out_free:
    kfree(xent);
    return err;
}