Re: [PATCH] cifs: Possible slab memory corruption while updating extended stats

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On Thu, Feb 3, 2011 at 2:10 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Thu,  3 Feb 2011 13:55:59 -0600
> shirishpargaonkar@xxxxxxxxx wrote:
>
>> From: Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx>
>>
>>
>> Updating extended statistics here can cause slab memory corruption
>> when callback functions frees (mid_entry) slab memory.
>>
>>
>> Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx>
>> ---
>>  fs/cifs/connect.c |    3 ---
>>  1 files changed, 0 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
>> index 945b220..f3c5ea6 100644
>> --- a/fs/cifs/connect.c
>> +++ b/fs/cifs/connect.c
>> @@ -635,9 +635,6 @@ multi_t2_fnd:
>>                               mid_entry->midState = MID_RESPONSE_RECEIVED;
>>                               list_del_init(&mid_entry->qhead);
>>                               mid_entry->callback(mid_entry);
>> -#ifdef CONFIG_CIFS_STATS2
>> -                             mid_entry->when_received = jiffies;
>> -#endif
>>                               break;
>>                       }
>>                       mid_entry = NULL;
>> --
>> 1.6.0.2
>>
>
>
> Good catch.
>
> Would it be better to move this up above the call to "callback" instead
> of eliminating it? I'm not so sure about the value of those stats, but
> it seems like they'll be wrong if you eliminate those lines altogether.

I have used them multiple times in debugging server problems
(timing when request received helps determine when
server is slow)


-- 
Thanks,

Steve
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