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Re: [PATCH V2] xfs_repair: test for bad level in dir2 node

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [PATCH V2] xfs_repair: test for bad level in dir2 node
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Tue, 10 Sep 2013 13:03:03 -0500
Cc: "'linux-xfs@xxxxxxxxxxx'" <linux-xfs@xxxxxxxxxxx>
Delivered-to: linux-xfs@xxxxxxxxxxx
In-reply-to: <522F55B9.3030509@xxxxxxxxxxx>
References: <52274F96.2010702@xxxxxxxxxxx> <522F4001.8010104@xxxxxxxxxxx> <522F4C26.2080106@xxxxxxx> <522F55B9.3030509@xxxxxxxxxxx>
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On 09/10/13 12:24, Eric Sandeen wrote:
On 9/10/13 11:43 AM, Mark Tinguely wrote:
On 09/10/13 10:51, 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.

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@xxxxxxx>
Signed-off-by: Eric Sandeen<sandeen@xxxxxxxxxx>
---

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..24db351 100644
--- a/repair/dir2.c
+++ b/repair/dir2.c
@@ -220,6 +220,15 @@ _("bad record count in inode %" PRIu64 ", count = %d, max = 
%d\n"),
            */
           if (i == -1) {
               i = da_cursor->active = nodehdr.level;
+            /* Tests above ensure that we have NODE_MAGIC here */
+            if (i == 0) {
+                do_warn(
+_("bad level 0 in interior node 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"),


But moving the check out of the (i == -1) block, then the loop can check all 
the intermediate nodes along the way and also the ending leaf.

--Mark.



Let me think about this.

There is already some level consistency checking at each level:

                         if (nodehdr.level == i - 1)  {
                                 i--;
                         } else  {
                                 do_warn(
_("bad directory btree for directory inode %" PRIu64 "\n"),
...
                                 goto error_out;


but I guess maybe we could check _magic_ more carefully on other levels.  Is 
that what you mean?

Hm, but as I cited above, we *already* check that either:

1) The block magc is LEAFN.  If so, we stop.  We warn if it's not root level 
(but don't fix?  Maybe that's a bug for another patch?)

Yes. We do not loop if "i == 1", so another LEAF should not be found.

2) The block magic is NODE.  If not, we error out.

Yes.

and as I showed above:
3) The level matches each level we're at in the loop.

So:

Any block which isnt' LEAFN or NODE is caught prior to the (i == -1) block.

Yes must be a NODE.

Any block which has a level that doesn't match is caught on the else of the (i 
== -1) block.

Yes, and "i" has to be larger than 1 because of the loop. Which I did not catch before.

And those are the only 2 valid types here.

What case is missing?

-eric


With loop condition of "i > 1" then it cannot miss what I first thought was being missed, but the level of 1 being a leaf is not checked.

--Mark.

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