netdev - Re: [PATCH net] sctp: jsctp_sf_eat_sack: fix kernel NULL ptr dereference

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Date:	Sat, 15 Dec 2012 20:58:23 +0100
From:	Daniel Borkmann <danborkmann@...earbox.net>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] sctp: jsctp_sf_eat_sack: fix kernel NULL ptr dereference

On Fri, Dec 14, 2012 at 10:49 PM, Daniel Borkmann
<danborkmann@...earbox.net> wrote:
> On Fri, Dec 14, 2012 at 5:57 PM, Daniel Borkmann <dborkman@...hat.com> wrote:
>> On 12/14/2012 04:12 PM, Vlad Yasevich wrote:
>>> On 12/14/2012 09:27 AM, Daniel Borkmann wrote:
>>>>
>>>> During debugging a sctp problem, I hit a kernel NULL pointer
>>>> dereference in the jprobes callback jsctp_sf_eat_sack(). This
>>>> small patch fixes the panic.
>>>>
>>>> Cc: Vlad Yasevich <vyasevich@...il.com>
>>>> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
>>>> ---
>>>>   net/sctp/probe.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/sctp/probe.c b/net/sctp/probe.c
>>>> index bc6cd75..0a4e9d6 100644
>>>> --- a/net/sctp/probe.c
>>>> +++ b/net/sctp/probe.c
>>>> @@ -134,7 +134,7 @@ sctp_disposition_t jsctp_sf_eat_sack(const struct
>>>> sctp_endpoint *ep,
>>>>
>>>>       sp = asoc->peer.primary_path;
>>>>
>>>> -    if ((full || sp->cwnd != lcwnd) &&
>>>> +    if (sp && (full || sp->cwnd != lcwnd) &&
>>>>           (!port || asoc->peer.port == port ||
>>>>            ep->base.bind_addr.port == port)) {
>>>>           lcwnd = sp->cwnd;
>>>
>>> Sorry, but this patch isn't making much sense.  @sp points to the primary
>>> path of the association and that can not be null if we receiving
>>> SACKs on this association.
>>>
>>> sctp_sf_eat_sack_6_2(), which we are probing, is only called while the
>>> association is valid and all the transports still exist.  It is also called
>>> under lock, so the transports can not go away while processing of the SACK.
>>> So unless there is some kind of jprobe issue, the pointer
>>> you are looking at should always be valid.
>>
>> Okay, I'll dig a bit deeper into that over the weekend.
>
> That's just for the record, I'll do further tests / debugging tomorrow ...
>
> I compiled the net kernel with kprobes selftest / sanity test
> (kernel/test_kprobes.c) and it passed:
>
> [    2.978082] Kprobe smoke test started
> [    3.034014] Kprobe smoke test passed successfully
>
> There, also jprobes are tested.

Found the problem, will send a new patch for the net tree in a couple
of minutes.
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