Re: [RFC PATCH] udp: don't rereference dst_entry dev pointer on rcv

Eric Dumazet
2013-04-11T17:53:26Z

On Thu, 2013-04-11 at 09:32 -0700, Eric Dumazet wrote:

> Short update : I do not understand yet why this patch is not working.
>
> Normally, the reassembled packet should get the dst from the last skb
> (the one completing the packet)...
>
> I have to make more experiments.

OK I think I've nailed it, please try following patch (I tried it on
net-next, but it should apply on previous kernels)

Thanks !

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 9385206..f8f1a87 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -494,9 +494,16 @@ found:
qp->q.max_size = skb->len + ihl;

if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
- qp->q.meat == qp->q.len)
- return ip_frag_reasm(qp, prev, dev);
+ qp->q.meat == qp->q.len) {
+ unsigned long dst_save = skb->_skb_refdst;

+ skb->_skb_refdst = 0;
+ err = ip_frag_reasm(qp, prev, dev);
+ skb->_skb_refdst = dst_save;
+ return err;
+ }
+
+ skb_dst_drop(skb);
inet_frag_lru_move(&qp->q);
return -EINPROGRESS;

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index e6e44ce..aac7fa5 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -342,9 +342,17 @@ found:
}

if (fq->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
- fq->q.meat == fq->q.len)
- return ip6_frag_reasm(fq, prev, dev);
+ fq->q.meat == fq->q.len) {
+ int err;
+ unsigned long dstsave = skb->_skb_refdst;
+
+ skb->_skb_refdst = 0;
+ err = ip6_frag_reasm(fq, prev, dev);
+ skb->_skb_refdst = dstsave;
+ return err;
+ }

+ skb_dst_drop(skb);
inet_frag_lru_move(&fq->q);
return -1;