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btrfs: fix invalid removal of root ref

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If we have the following sequence of events

  btrfs sub create A
  btrfs sub create A/B
  btrfs sub snap A C
  mkdir C/foo
  mv A/B C/foo
  rm -rf *

We will end up with a transaction abort.

The reason for this is because we create a root ref for B pointing to A.
When we create a snapshot of C we still have B in our tree, but because
the root ref points to A and not C we will make it appear to be empty.

The problem happens when we move B into C.  This removes the root ref
for B pointing to A and adds a ref of B pointing to C.  When we rmdir C
we'll see that we have a ref to our root and remove the root ref,
despite not actually matching our reference name.

Now btrfs_del_root_ref() allowing this to work is a bug as well, however
we know that this inode does not actually point to a root ref in the
first place, so we shouldn't be calling btrfs_del_root_ref() in the
first place and instead simply look up our dir index for this item and
do the rest of the removal.

CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2019-12-18 17:20:28 -05:00 committed by David Sterba
parent 045d3967b6
commit d49d3287e7
1 changed files with 19 additions and 8 deletions
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27
fs/btrfs/inode.c
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@ -4283,13 +4283,16 @@ static int btrfs_unlink_subvol(struct btrfs_trans_handle *trans,
}
btrfs_release_path(path);
ret = btrfs_del_root_ref(trans, objectid, root->root_key.objectid,
dir_ino, &index, name, name_len);
if (ret < 0) {
if (ret != -ENOENT) {
btrfs_abort_transaction(trans, ret);
goto out;
}
/*
* This is a placeholder inode for a subvolume we didn't have a
* reference to at the time of the snapshot creation. In the meantime
* we could have renamed the real subvol link into our snapshot, so
* depending on btrfs_del_root_ref to return -ENOENT here is incorret.
* Instead simply lookup the dir_index_item for this entry so we can
* remove it. Otherwise we know we have a ref to the root and we can
* call btrfs_del_root_ref, and it _shouldn't_ fail.
*/
if (btrfs_ino(inode) == BTRFS_EMPTY_SUBVOL_DIR_OBJECTID) {
di = btrfs_search_dir_index_item(root, path, dir_ino,
name, name_len);
if (IS_ERR_OR_NULL(di)) {
@ -4304,8 +4307,16 @@ static int btrfs_unlink_subvol(struct btrfs_trans_handle *trans,
leaf = path->nodes[0];
btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
index = key.offset;
btrfs_release_path(path);
} else {
ret = btrfs_del_root_ref(trans, objectid,
root->root_key.objectid, dir_ino,
&index, name, name_len);
if (ret) {
btrfs_abort_transaction(trans, ret);
goto out;
}
}
btrfs_release_path(path);
ret = btrfs_delete_delayed_dir_index(trans, BTRFS_I(dir), index);
if (ret) {