Re: [PATCH] xfs_repair: skip freelist scan of dodgy agf in no-modify mode

Eric Sandeen
2013-03-02T01:30:37Z

On Mar 1, 2013, at 7:18 PM, Dave Chinner <david@fromorbit.com> wrote:

> On Fri, Mar 01, 2013 at 05:46:48PM -0600, Eric Sandeen wrote:
>> In no-modify mode (-n), verify_set_agf doesn't fix up bad
>> freelist blocks that it finds. When we get to scan_freelist,
>> this can wreak havoc if, for example, first > last and the loop
>> never exits; we index agfl->agfl_bno[i] off into the weeds.
>>
>> To fix this, re-check the values in no-modify mode, and if
>> they're off, warn about it and skip the scan.
>>
>> In addition, add a check to verify_set_agf() to ensure that
>> first <= last.
>>
>> Reported-by: Ole Tange <tange@binf.ku.dk>
>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>> ---
>>
>> diff --git a/repair/agheader.c b/repair/agheader.c
>> index 769022d..68789fe 100644
>> --- a/repair/agheader.c
>> +++ b/repair/agheader.c
>> @@ -86,6 +86,14 @@ verify_set_agf(xfs_mount_t *mp, xfs_agf_t *agf, xfs_agnumber_t i)
>> * check first/last AGF fields. if need be, lose the free
>> * space in the AGFL, we'll reclaim it later.
>> */
>> + if (be32_to_cpu(agf->agf_flfirst) > be32_to_cpu(agf->agf_fllast)) {
>> + do_warn(_("flfirst %d in agf %d > fllast %d\n"),
>> + be32_to_cpu(agf->agf_flfirst),
>> + i, be32_to_cpu(agf->agf_fllast));
>> + if (!no_modify)
>> + agf->agf_fllast = agf->agf_flfirst = cpu_to_be32(0);
>> + }
>
> I don't think that test is correct. The free list is circular and is
> indexed as a pair of head/tail pointers. Hence flfirst > fllast can
> be actually valid. e.g. flcount = 4, flfirst=126, fllast = 2 is a
> valid free list.
>
Doh, ok. Will fix.
>> +
>> if (be32_to_cpu(agf->agf_flfirst) >= XFS_AGFL_SIZE(mp)) {
>> do_warn(_("flfirst %d in agf %d too large (max = %zu)\n"),
>> be32_to_cpu(agf->agf_flfirst),
>> diff --git a/repair/scan.c b/repair/scan.c
>> index 5345094..0f83fb4 100644
>> --- a/repair/scan.c
>> +++ b/repair/scan.c
>> @@ -1067,6 +1067,17 @@ scan_freelist(
>> }
>> agfl = XFS_BUF_TO_AGFL(agflbuf);
>> i = be32_to_cpu(agf->agf_flfirst);
>> + if (no_modify) {
>> + /* agf values not sanitized, so double check */
>> + if (i >= XFS_AGFL_SIZE(mp) ||
>> + be32_to_cpu(agf->agf_fllast) >= XFS_AGFL_SIZE(mp) ||
>> + i > be32_to_cpu(agf->agf_fllast))
>> + do_warn(_("agf %d freelist blocks bad, skipping scan\n"),
>
> "skipping freelist scan"
>
>> + i);
>> + return;
>
> Also, you might be missing a set of {} there - that will always
> return immediately if no_modify is set....
>
Cripes. 1 demerit for me, sorry. Will fix and resend.

Thanks for the embarrassing review. :)

-Eric

> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com