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

To: Michael Maier <m1278468@xxxxxxxxxxx>
Subject: Re: [PATCH] xfs_repair: zero out unused parts of superblocks
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Fri, 16 Aug 2013 10:05:35 -0500
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <520D0A15.1050304@xxxxxxxxxxx>
References: <520C3C60.3090500@xxxxxxxxxx> <520D0A15.1050304@xxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
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@xxxxxxxxxxx>
>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>> ---
>>
>> 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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