[PATCH V3] xfs_repair: test for bad level in dir2 node

[Eric Sandeen <sandeen@sandeen.net>]

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.

By the time the level 0 test is done, we have already ensured that
this block has XFS_DA[3]_NODE_MAGIC.

Reported-by: Jan Yves Brueckner <jyb@gmx.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

V3: Simplify the test.

Mark, Dave, I know you had some concerns about other conditions being
tested, but I think those are separate from this fix, which simply ensures
that the level we find for this _NODE block is within the valid range
for a node.  (It also matches the test currently present in xfs_check).

If we've got other missing conditions, those can be other patches,
I think.

V2: Drop re-test of hdr magic which is guaranteed to be NODE at this point.
    fix "interior inode" - s/b "interior node"

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..e82ca7d 100644
--- a/repair/dir2.c
+++ b/repair/dir2.c
@@ -220,7 +220,7 @@ _("bad record count in inode %" PRIu64 ", count = %d, max = %d\n"),
 		 */
 		if (i == -1) {
 			i = da_cursor->active = nodehdr.level;
-			if (i >= XFS_DA_NODE_MAXDEPTH) {
+			if (i < 1 || i >= XFS_DA_NODE_MAXDEPTH) {
 				do_warn(
 _("bad header depth for directory inode %" PRIu64 "\n"),
 					da_cursor->ino);

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