[B.A.T.M.A.N.] [PATCH] batman-adv-kernelland: Fix memory corruption bug

Scott Raynel scottraynel at gmail.com
Fri Dec 12 09:08:01 UTC 2008


Hi Simon,

On 6/12/2008, at 8:51 AM, Simon Wunderlich wrote:

> Hey Scott,
>
> On Fri, Dec 05, 2008 at 11:40:30PM +1300, Scott Raynel wrote:
>> Hi Simon,
>>
>> On 5/12/2008, at 12:35 AM, Simon Wunderlich wrote:
>>
>>> Hey Scott,
>>>
>>> thank you very much for the fix! Can you confirm if this bug is
>>> related
>>> to https://dev.open-mesh.net/batman/ticket/86 ?
>>> This bug has very likely been caused by a memory corruption, but i
>>> couldn´t find where. (i have not experienced any kernel panics by
>>> this
>>> however ...).
>>
>>
>> It is quite possible that they are related. The slab error states  
>> that
>> a memory allocation was overwritten - the same problem as my patch
>> fixed. However, I can't confirm whether it is the same memory
>> allocation or a different one. The stack trace I got specifically
>> mentioned the kfree() in send_own_packet(), whereas this stack trace
>> does not.
>>
>> Is that bug easily reproducible? It will be a couple of days before I
>> can try to look at it.
>
> Yep, it was quite easy: just turn it on and off a few times. (echo
> device and nothing into /proc/net/batman-adv/interfaces). The warning
> appeared after 10 times in my qemu instance. No crash, only this  
> warning.

I can't reproduce this bug before my patch is applied because the bug  
it fixes always gets in the way :)

After applying the patch I seem to be able to consistently lock up the  
system by adding and removing an interface from the batman device  
several times. The box still replies to pings, but I can't SSH in.  
This does not trigger the slab debugger. I've looked at using the  
magic sysreq interface to see what's going on and by printing the  
current task it appears to be hanging during the  
cancel_rearming_delayed_work() call in shutdown_module(). This might  
be related to the scheduling-while-atomic bugs. I'll keep looking into  
this as I get time, but things are pretty busy here at the moment.

Cheers,


--
Scott Raynel
WAND Network Research Group
Department of Computer Science
University of Waikato
New Zealand







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