Re: [PATCH] xfs_repair: test for bad level in dir2 node

Dave Chinner
2013-09-10T00:46:14Z

On Wed, Sep 04, 2013 at 10:19:50AM -0500, Eric Sandeen wrote:
> In traverse_int_dir2block(), the variable 'i' is the level in
> the tree, with 0 being a leaf node. In the "do" loop we
> start at the root, and work our way down to a leaf.
>
> If the first node we read is an interior node with NODE_MAGIC,
> but it tells us that its level is 0 (a leaf), this is clearly
> an inconsistency.
>
> Worse, we'd return with success, bno set, and only level[0]
> in the cursor initialized. Then down this path we'll
> segfault when accessing an uninitialized (and zeroed) member
> of the cursor's level array:
>
> process_node_dir2
> traverse_int_dir2block // returns 0 w/ bno set, only level[0] init'd
> process_leaf_level_dir2
> verify_dir2_path(mp, da_cursor, 0) // p_level == 0
> this_level = p_level + 1;
> node = cursor->level[this_level].bp->b_addr; // level[1] uninit & 0'd
>
> Fix this by recognizing that an interior node w/ level 0 is invalid, and
> error out as for other inconsistencies.
>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
>
> My only testcase for this is Jan Yves Brueckner's badly corrupted
> filesystem image. With this change, we get i.e. :
>
> +bad level in interior inode for directory inode 39869938
> +corrupt block 6 in directory inode 39869957
> + will junk block
>
> diff --git a/repair/dir2.c b/repair/dir2.c
> index 05bd4b7..20c6e1a 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -220,6 +220,16 @@ _("bad record count in inode %" PRIu64 ", count = %d, max = %d\n"),
> */
> if (i == -1) {
> i = da_cursor->active = nodehdr.level;
> + if (i == 0 &&
> + (nodehdr.magic == XFS_DA_NODE_MAGIC ||
> + nodehdr.magic == XFS_DA3_NODE_MAGIC)) {
> + do_warn(
> +_("bad level 0 in interior inode for directory inode %" PRIu64 "\n"),
> + da_cursor->ino);
> + libxfs_putbuf(bp);
> + i = -1;
> + goto error_out;
> + }
> if (i >= XFS_DA_NODE_MAXDEPTH) {
> do_warn(
> _("bad header depth for directory inode %" PRIu64 "\n"),

Looks sane, though wouldn't it be better to check for the correct
header magic number (i.e LEAF1/LEAFN) here? i.e. if we are at level
zero and we don't have a leaf, then there's something wrong. This
will only catch the case of a node replacing a leaf, not a free
space block or data block being at the wrong place...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com