[SCTP]: Always linearise packet on input

I was looking at a RHEL5 bug report involving Xen and SCTP
(https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=212550).
It turns out that SCTP wasn't written to handle skb fragments at
all.  The absence of any calls to skb_may_pull is testament to
that.

It just so happens that Xen creates fragmented packets more often
than other scenarios (header & data split when going from domU to
dom0).  That's what caused this bug to show up.

Until someone has the time sits down and audits the entire net/sctp
directory, here is a conservative and safe solution that simply
linearises all packets on input.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 64f630102532..99c0501ca513 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -135,6 +135,9 @@ int sctp_rcv(struct sk_buff *skb)
 
         SCTP_INC_STATS_BH(SCTP_MIB_INSCTPPACKS);
 
+        if (skb_linearize(skb))
+                goto discard_it;
+
         sh = (struct sctphdr *) skb->h.raw;
 
         /* Pull up the IP and SCTP headers. */