Re: panic in skb_push via sctp

[Daniel Borkmann]

On 12/01/2014 07:02 PM, Robert ÅwiÄcki wrote:
> Thanks for looking into it. I can try with your patch, but no
> guarantees that the fuzzer will hit the same condition in some
> reasonable time-frame. Will get back in some time with results.

Ok, thanks!

> PS. If you think it's possible to create a repro (userland code) which
> can trigger this, I can give it a try.

Did by accident trinity create tunnels? It looks that upper layer
protocols (except SCTP) all allocate and reserve MAX_HEADER to
accommodate enough head room in worst case for possible tunnels.

> 2014-12-01 18:36 GMT+01:00 Daniel Borkmann <dborkman@xxxxxxxxxx>:
> > On 12/01/2014 05:49 PM, Robert ÅwiÄcki wrote:
> > > I don't have much more, cause my kernel is kASLRNized and gdb cannot
> > > handle that, but pasting output from kdb. Maybe somebody will be able
> > > to see something obvious.
> > >
> > >    <0>[93699.703244] skbuff: skb_under_panic: text:ffffffff83cff03e
> > > len:104 put:56 head:ffff8803bd804ec0 data:ffff8803bd804ebc tail:0x64
> > > end:0xc0 dev:<NULL>
> >
> >
> > Thanks for the report!
> >
> > On a first view, it looks like we should be using MAX_HEADER instead
> > of LL_MAX_HEADER here, could you try with the following patch:
> >
> > diff --git a/net/sctp/output.c b/net/sctp/output.c
> > index 42dffd4..fc5e45b 100644
> > --- a/net/sctp/output.c
> > +++ b/net/sctp/output.c
> > @@ -401,12 +401,12 @@ int sctp_packet_transmit(struct sctp_packet *packet)
> >          sk = chunk->skb->sk;
> >
> >          /* Allocate the new skb.  */
> > -       nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
> > +       nskb = alloc_skb(packet->size + MAX_HEADER, GFP_ATOMIC);
> >          if (!nskb)
> >                  goto nomem;
> >
> >          /* Make sure the outbound skb has enough header room reserved. */
> > -       skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
> > +       skb_reserve(nskb, packet->overhead + MAX_HEADER);
> >
> >          /* Set the owning socket so that we know where to get the
> >           * destination IP address.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/