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

To: "'linux-xfs@xxxxxxxxxxx'" <linux-xfs@xxxxxxxxxxx>
Subject: [PATCH V2] xfs_repair: test for bad level in dir2 node
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 10 Sep 2013 10:51:29 -0500
Delivered-to: linux-xfs@xxxxxxxxxxx
In-reply-to: <52274F96.2010702@xxxxxxxxxxx>
References: <52274F96.2010702@xxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
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:

  traverse_int_dir2block  // returns 0 w/ bno set, only level[0] init'd
    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) {
 _("bad header depth for directory inode %" PRIu64 "\n"),

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