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

Mark Tinguely
2013-09-10T18:03:07Z

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@gmx.com>
>>> Signed-off-by: Eric Sandeen<sandeen@redhat.com>
>>> ---
>>>
>>> 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.