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Re: [PATCH 3/4] xfs_logprint: fix some unaligned accesses

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 3/4] xfs_logprint: fix some unaligned accesses
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Fri, 9 Oct 2015 08:48:08 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20151009132440.GD27982@xxxxxxxxxxxxxxx>
References: <56170906.5090301@xxxxxxxxxx> <5617098E.9090102@xxxxxxxxxxx> <20151009132440.GD27982@xxxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 10/9/15 8:24 AM, Brian Foster wrote:
> On Thu, Oct 08, 2015 at 07:25:50PM -0500, Eric Sandeen wrote:
>> This routine had a fair bit of gyration to avoid unaligned accesses,
>> but didn't fix them all.  Fix some more spotted at runtime by libubsan.
>>
>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>> ---
>>  logprint/log_misc.c |   18 +++++++++++++++---
>>  repair/btree.c      |    1 +
>>  2 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/logprint/log_misc.c b/logprint/log_misc.c
>> index d76145c..6cd249a 100644
>> --- a/logprint/log_misc.c
>> +++ b/logprint/log_misc.c
>> @@ -325,7 +325,11 @@ xlog_print_trans_buffer(char **ptr, int len, int *i, 
>> int num_ops)
>>              }
>>              super_block = 0;
>>      } else if (be32_to_cpu(*(__be32 *)(*ptr)) == XFS_AGI_MAGIC) {
>> -            agi = (xfs_agi_t *)(*ptr);
>> +            struct xfs_agi agi_s;
>> +
>> +            /* memmove because *ptr may not be 8-byte aligned */
>> +            memmove(&agi_s, *ptr, sizeof(struct xfs_agi));
>> +            agi = &agi_s;
> 
> Nit: could we either define the new variables in the same scope as the
> pointer (either here or at the top of the function), or just ditch the
> pointers altogether?

Let me see how that looks, sure.

>>              printf(_("AGI Buffer: XAGI  "));
>>              /*
>>               * v4 filesystems only contain the fields before the uuid.
> ...
>> diff --git a/repair/btree.c b/repair/btree.c
>> index 66fb40b..e31e67a 100644
>> --- a/repair/btree.c
>> +++ b/repair/btree.c
>> @@ -230,6 +230,7 @@ btree_get_next(
>>      }
>>      if (level == 0) {
>>              if (key) {
>> +            /* XXXX what if index past MAX?  What if no next? */
> 
> Unintentional hunk?

Yeah, dammit, I thought I removed that, sorry.

Thanks,
-Eric

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