![Filipe Manana](/assets/img/avatar_default.png)
Replacing a xattr consists of doing a lookup for its existing value, delete the current value from the respective leaf, release the search path and then finally insert the new value. This leaves a time window where readers (getxattr, listxattrs) won't see any value for the xattr. Xattrs are used to store ACLs, so this has security implications. This change also fixes 2 other existing issues which were: *) Deleting the old xattr value without verifying first if the new xattr will fit in the existing leaf item (in case multiple xattrs are packed in the same item due to name hash collision); *) Returning -EEXIST when the flag XATTR_CREATE is given and the xattr doesn't exist but we have have an existing item that packs muliple xattrs with the same name hash as the input xattr. In this case we should return ENOSPC. A test case for xfstests follows soon. Thanks to Alexandre Oliva for reporting the non-atomicity of the xattr replace implementation. Reported-by: Alexandre Oliva <oliva@gnu.org> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
489 lines
13 KiB
C
489 lines
13 KiB
C
/*
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* Copyright (C) 2007 Red Hat. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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*/
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/slab.h>
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#include <linux/rwsem.h>
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#include <linux/xattr.h>
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#include <linux/security.h>
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#include <linux/posix_acl_xattr.h>
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#include "ctree.h"
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#include "btrfs_inode.h"
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#include "transaction.h"
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#include "xattr.h"
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#include "disk-io.h"
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#include "props.h"
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#include "locking.h"
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ssize_t __btrfs_getxattr(struct inode *inode, const char *name,
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void *buffer, size_t size)
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{
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struct btrfs_dir_item *di;
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struct btrfs_root *root = BTRFS_I(inode)->root;
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struct btrfs_path *path;
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struct extent_buffer *leaf;
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int ret = 0;
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unsigned long data_ptr;
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path = btrfs_alloc_path();
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if (!path)
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return -ENOMEM;
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/* lookup the xattr by name */
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di = btrfs_lookup_xattr(NULL, root, path, btrfs_ino(inode), name,
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strlen(name), 0);
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if (!di) {
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ret = -ENODATA;
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goto out;
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} else if (IS_ERR(di)) {
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ret = PTR_ERR(di);
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goto out;
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}
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leaf = path->nodes[0];
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/* if size is 0, that means we want the size of the attr */
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if (!size) {
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ret = btrfs_dir_data_len(leaf, di);
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goto out;
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}
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/* now get the data out of our dir_item */
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if (btrfs_dir_data_len(leaf, di) > size) {
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ret = -ERANGE;
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goto out;
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}
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/*
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* The way things are packed into the leaf is like this
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* |struct btrfs_dir_item|name|data|
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* where name is the xattr name, so security.foo, and data is the
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* content of the xattr. data_ptr points to the location in memory
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* where the data starts in the in memory leaf
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*/
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data_ptr = (unsigned long)((char *)(di + 1) +
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btrfs_dir_name_len(leaf, di));
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read_extent_buffer(leaf, buffer, data_ptr,
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btrfs_dir_data_len(leaf, di));
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ret = btrfs_dir_data_len(leaf, di);
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out:
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btrfs_free_path(path);
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return ret;
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}
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static int do_setxattr(struct btrfs_trans_handle *trans,
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struct inode *inode, const char *name,
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const void *value, size_t size, int flags)
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{
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struct btrfs_dir_item *di = NULL;
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struct btrfs_root *root = BTRFS_I(inode)->root;
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struct btrfs_path *path;
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size_t name_len = strlen(name);
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int ret = 0;
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if (name_len + size > BTRFS_MAX_XATTR_SIZE(root))
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return -ENOSPC;
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path = btrfs_alloc_path();
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if (!path)
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return -ENOMEM;
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path->skip_release_on_error = 1;
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if (!value) {
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di = btrfs_lookup_xattr(trans, root, path, btrfs_ino(inode),
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name, name_len, -1);
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if (!di && (flags & XATTR_REPLACE))
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ret = -ENODATA;
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else if (di)
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ret = btrfs_delete_one_dir_name(trans, root, path, di);
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goto out;
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}
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/*
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* For a replace we can't just do the insert blindly.
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* Do a lookup first (read-only btrfs_search_slot), and return if xattr
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* doesn't exist. If it exists, fall down below to the insert/replace
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* path - we can't race with a concurrent xattr delete, because the VFS
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* locks the inode's i_mutex before calling setxattr or removexattr.
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*/
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if (flags & XATTR_REPLACE) {
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ASSERT(mutex_is_locked(&inode->i_mutex));
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di = btrfs_lookup_xattr(NULL, root, path, btrfs_ino(inode),
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name, name_len, 0);
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if (!di) {
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ret = -ENODATA;
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goto out;
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}
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btrfs_release_path(path);
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di = NULL;
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}
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ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
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name, name_len, value, size);
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if (ret == -EOVERFLOW) {
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/*
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* We have an existing item in a leaf, split_leaf couldn't
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* expand it. That item might have or not a dir_item that
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* matches our target xattr, so lets check.
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*/
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ret = 0;
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btrfs_assert_tree_locked(path->nodes[0]);
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di = btrfs_match_dir_item_name(root, path, name, name_len);
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if (!di && !(flags & XATTR_REPLACE)) {
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ret = -ENOSPC;
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goto out;
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}
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} else if (ret == -EEXIST) {
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ret = 0;
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di = btrfs_match_dir_item_name(root, path, name, name_len);
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ASSERT(di); /* logic error */
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} else if (ret) {
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goto out;
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}
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if (di && (flags & XATTR_CREATE)) {
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ret = -EEXIST;
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goto out;
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}
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if (di) {
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/*
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* We're doing a replace, and it must be atomic, that is, at
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* any point in time we have either the old or the new xattr
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* value in the tree. We don't want readers (getxattr and
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* listxattrs) to miss a value, this is specially important
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* for ACLs.
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*/
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const int slot = path->slots[0];
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struct extent_buffer *leaf = path->nodes[0];
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const u16 old_data_len = btrfs_dir_data_len(leaf, di);
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const u32 item_size = btrfs_item_size_nr(leaf, slot);
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const u32 data_size = sizeof(*di) + name_len + size;
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struct btrfs_item *item;
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unsigned long data_ptr;
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char *ptr;
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if (size > old_data_len) {
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if (btrfs_leaf_free_space(root, leaf) <
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(size - old_data_len)) {
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ret = -ENOSPC;
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goto out;
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}
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}
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if (old_data_len + name_len + sizeof(*di) == item_size) {
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/* No other xattrs packed in the same leaf item. */
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if (size > old_data_len)
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btrfs_extend_item(root, path,
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size - old_data_len);
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else if (size < old_data_len)
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btrfs_truncate_item(root, path, data_size, 1);
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} else {
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/* There are other xattrs packed in the same item. */
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ret = btrfs_delete_one_dir_name(trans, root, path, di);
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if (ret)
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goto out;
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btrfs_extend_item(root, path, data_size);
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}
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item = btrfs_item_nr(slot);
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ptr = btrfs_item_ptr(leaf, slot, char);
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ptr += btrfs_item_size(leaf, item) - data_size;
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di = (struct btrfs_dir_item *)ptr;
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btrfs_set_dir_data_len(leaf, di, size);
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data_ptr = ((unsigned long)(di + 1)) + name_len;
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write_extent_buffer(leaf, value, data_ptr, size);
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btrfs_mark_buffer_dirty(leaf);
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} else {
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/*
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* Insert, and we had space for the xattr, so path->slots[0] is
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* where our xattr dir_item is and btrfs_insert_xattr_item()
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* filled it.
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*/
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}
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out:
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btrfs_free_path(path);
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return ret;
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}
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/*
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* @value: "" makes the attribute to empty, NULL removes it
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*/
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int __btrfs_setxattr(struct btrfs_trans_handle *trans,
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struct inode *inode, const char *name,
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const void *value, size_t size, int flags)
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{
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struct btrfs_root *root = BTRFS_I(inode)->root;
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int ret;
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if (trans)
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return do_setxattr(trans, inode, name, value, size, flags);
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trans = btrfs_start_transaction(root, 2);
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if (IS_ERR(trans))
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return PTR_ERR(trans);
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ret = do_setxattr(trans, inode, name, value, size, flags);
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if (ret)
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goto out;
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inode_inc_iversion(inode);
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inode->i_ctime = CURRENT_TIME;
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set_bit(BTRFS_INODE_COPY_EVERYTHING, &BTRFS_I(inode)->runtime_flags);
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ret = btrfs_update_inode(trans, root, inode);
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BUG_ON(ret);
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out:
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btrfs_end_transaction(trans, root);
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return ret;
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}
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ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
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{
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struct btrfs_key key, found_key;
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struct inode *inode = dentry->d_inode;
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struct btrfs_root *root = BTRFS_I(inode)->root;
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struct btrfs_path *path;
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struct extent_buffer *leaf;
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struct btrfs_dir_item *di;
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int ret = 0, slot;
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size_t total_size = 0, size_left = size;
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unsigned long name_ptr;
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size_t name_len;
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/*
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* ok we want all objects associated with this id.
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* NOTE: we set key.offset = 0; because we want to start with the
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* first xattr that we find and walk forward
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*/
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key.objectid = btrfs_ino(inode);
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key.type = BTRFS_XATTR_ITEM_KEY;
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key.offset = 0;
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path = btrfs_alloc_path();
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if (!path)
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return -ENOMEM;
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path->reada = 2;
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/* search for our xattrs */
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ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
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if (ret < 0)
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goto err;
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while (1) {
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leaf = path->nodes[0];
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slot = path->slots[0];
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/* this is where we start walking through the path */
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if (slot >= btrfs_header_nritems(leaf)) {
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/*
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* if we've reached the last slot in this leaf we need
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* to go to the next leaf and reset everything
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*/
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ret = btrfs_next_leaf(root, path);
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if (ret < 0)
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goto err;
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else if (ret > 0)
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break;
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continue;
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}
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btrfs_item_key_to_cpu(leaf, &found_key, slot);
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/* check to make sure this item is what we want */
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if (found_key.objectid != key.objectid)
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break;
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if (found_key.type != BTRFS_XATTR_ITEM_KEY)
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break;
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di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
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if (verify_dir_item(root, leaf, di))
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goto next;
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name_len = btrfs_dir_name_len(leaf, di);
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total_size += name_len + 1;
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/* we are just looking for how big our buffer needs to be */
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if (!size)
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goto next;
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if (!buffer || (name_len + 1) > size_left) {
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ret = -ERANGE;
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goto err;
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}
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name_ptr = (unsigned long)(di + 1);
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read_extent_buffer(leaf, buffer, name_ptr, name_len);
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buffer[name_len] = '\0';
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size_left -= name_len + 1;
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buffer += name_len + 1;
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next:
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path->slots[0]++;
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}
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ret = total_size;
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err:
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btrfs_free_path(path);
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return ret;
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}
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/*
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* List of handlers for synthetic system.* attributes. All real ondisk
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* attributes are handled directly.
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*/
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const struct xattr_handler *btrfs_xattr_handlers[] = {
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#ifdef CONFIG_BTRFS_FS_POSIX_ACL
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&posix_acl_access_xattr_handler,
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&posix_acl_default_xattr_handler,
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#endif
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NULL,
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};
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/*
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* Check if the attribute is in a supported namespace.
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*
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* This applied after the check for the synthetic attributes in the system
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* namespace.
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*/
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static bool btrfs_is_valid_xattr(const char *name)
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{
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return !strncmp(name, XATTR_SECURITY_PREFIX,
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XATTR_SECURITY_PREFIX_LEN) ||
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!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN) ||
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!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
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!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) ||
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!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN);
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}
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ssize_t btrfs_getxattr(struct dentry *dentry, const char *name,
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void *buffer, size_t size)
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{
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/*
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* If this is a request for a synthetic attribute in the system.*
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* namespace use the generic infrastructure to resolve a handler
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* for it via sb->s_xattr.
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*/
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if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
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return generic_getxattr(dentry, name, buffer, size);
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if (!btrfs_is_valid_xattr(name))
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return -EOPNOTSUPP;
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return __btrfs_getxattr(dentry->d_inode, name, buffer, size);
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}
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int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
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size_t size, int flags)
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{
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struct btrfs_root *root = BTRFS_I(dentry->d_inode)->root;
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/*
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* The permission on security.* and system.* is not checked
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* in permission().
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*/
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if (btrfs_root_readonly(root))
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return -EROFS;
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/*
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* If this is a request for a synthetic attribute in the system.*
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* namespace use the generic infrastructure to resolve a handler
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* for it via sb->s_xattr.
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*/
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if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
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return generic_setxattr(dentry, name, value, size, flags);
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if (!btrfs_is_valid_xattr(name))
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return -EOPNOTSUPP;
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if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
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return btrfs_set_prop(dentry->d_inode, name,
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value, size, flags);
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if (size == 0)
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value = ""; /* empty EA, do not remove */
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return __btrfs_setxattr(NULL, dentry->d_inode, name, value, size,
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flags);
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}
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int btrfs_removexattr(struct dentry *dentry, const char *name)
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{
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struct btrfs_root *root = BTRFS_I(dentry->d_inode)->root;
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/*
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* The permission on security.* and system.* is not checked
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* in permission().
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*/
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if (btrfs_root_readonly(root))
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return -EROFS;
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/*
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* If this is a request for a synthetic attribute in the system.*
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* namespace use the generic infrastructure to resolve a handler
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* for it via sb->s_xattr.
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*/
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if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
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return generic_removexattr(dentry, name);
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if (!btrfs_is_valid_xattr(name))
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return -EOPNOTSUPP;
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if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
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return btrfs_set_prop(dentry->d_inode, name,
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NULL, 0, XATTR_REPLACE);
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return __btrfs_setxattr(NULL, dentry->d_inode, name, NULL, 0,
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XATTR_REPLACE);
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}
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static int btrfs_initxattrs(struct inode *inode,
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const struct xattr *xattr_array, void *fs_info)
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{
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const struct xattr *xattr;
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struct btrfs_trans_handle *trans = fs_info;
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char *name;
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int err = 0;
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for (xattr = xattr_array; xattr->name != NULL; xattr++) {
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name = kmalloc(XATTR_SECURITY_PREFIX_LEN +
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strlen(xattr->name) + 1, GFP_NOFS);
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if (!name) {
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err = -ENOMEM;
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break;
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}
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strcpy(name, XATTR_SECURITY_PREFIX);
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strcpy(name + XATTR_SECURITY_PREFIX_LEN, xattr->name);
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err = __btrfs_setxattr(trans, inode, name,
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xattr->value, xattr->value_len, 0);
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kfree(name);
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if (err < 0)
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break;
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}
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return err;
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}
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int btrfs_xattr_security_init(struct btrfs_trans_handle *trans,
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struct inode *inode, struct inode *dir,
|
|
const struct qstr *qstr)
|
|
{
|
|
return security_inode_init_security(inode, dir, qstr,
|
|
&btrfs_initxattrs, trans);
|
|
}
|