Re: [PATCH] xfs_repair: zero out unused parts of superblocks

[Eric Sandeen <sandeen@redhat.com>]

On 8/15/13 12:04 PM, Michael Maier wrote:
> Eric Sandeen wrote:
>> Prior to:
>> 1375cb65 xfs: growfs: don't read garbage for new secondary superblocks
>>
>> we ran the risk of allowing garbage in secondary superblocks
>> beyond the in-use sb fields.  With kernels 3.10 and beyond, the
>> verifiers will kick these out as invalid, but xfs_repair does
>> not detect or repair this condition.
>>
>> There is superblock stale-data zeroing code, but it is under a
>> narrow conditional - the bug addressed in the above commit did not
>> meet that conditional.  So change this to check unconditionally.
>>
>> Further, the checking code was looking at the in-memory
>> superblock buffer, which was zeroed prior to population, and
>> would therefore never possibly show any stale data beyond the
>> last up-rev superblock field.
>>
>> So instead, check the disk buffer for this garbage condition.
>>
>> If we detect garbage, we must zero out both the in-memory sb
>> and the disk buffer; the former may contain unused data
>> in up-rev sb fields which will be written back out; the latter
>> may contain garbage beyond all fields, which won't be updated
>> when we translate the in-memory sb back to disk.
>>
>> The V4 superblock case was zeroing out the sb_bad_features2
>> field; we also fix that to leave that field alone.
>>
>> Lastly, use offsetof() instead of the tortured (__psint_t)
>> casts & pointer math.
>>
>> Reported-by: Michael Maier <m1278468@allmail.net>
>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>> ---
>>
>> Michael - this will need slight tweaking to apply against
>> older xfsprogs.
>>
>> Also:
>>
>> With more of Dave's changes, I think we can swap out:
>>
>> 		size = offsetof(xfs_sb_t, sb_lsn)
>> 			+ sizeof(sb->sb_lsn);
>> for
>> 		size = xfs_sb_info[XFS_SBS_LSN + 1].offset;
>>
>> but this version is a bit easier to backport, and works in the
>> current git tree...
> 
> I tested with current git tree and it worked as expected for me!
> Afterwards I was able to run xfs_growfs (from 3.1.11) w/o any problem.
> 
> Please excuse me - forgot to set the english locale before starting.
> Hope you can guess what it should be in english :-).
> 

Kein Problem, ich kann etwas Deutsch zu lesen. :)

Glad it worked for you!

-Eric

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