From 0992d67bc2bcd723d57c6ee7883bda4524450179 Mon Sep 17 00:00:00 2001 From: Guillaume Nault Date: Sat, 31 Oct 2020 01:07:25 +0100 Subject: mpls: drop skb's dst in mpls_forward() Commit 394de110a733 ("net: Added pointer check for dst->ops->neigh_lookup in dst_neigh_lookup_skb") added a test in dst_neigh_lookup_skb() to avoid a NULL pointer dereference. The root cause was the MPLS forwarding code, which doesn't call skb_dst_drop() on incoming packets. That is, if the packet is received from a collect_md device, it has a metadata_dst attached to it that doesn't implement any dst_ops function. To align the MPLS behaviour with IPv4 and IPv6, let's drop the dst in mpls_forward(). This way, dst_neigh_lookup_skb() doesn't need to test ->neigh_lookup any more. Let's keep a WARN condition though, to document the precondition and to ease detection of such problems in the future. Signed-off-by: Guillaume Nault Link: https://lore.kernel.org/r/f8c2784c13faa54469a2aac339470b1049ca6b63.1604102750.git.gnault@redhat.com Signed-off-by: Jakub Kicinski --- net/mpls/af_mpls.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'net/mpls/af_mpls.c') diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c index f2868a8a50c3..47bab701555f 100644 --- a/net/mpls/af_mpls.c +++ b/net/mpls/af_mpls.c @@ -377,6 +377,8 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev, if (!pskb_may_pull(skb, sizeof(*hdr))) goto err; + skb_dst_drop(skb); + /* Read and decode the label */ hdr = mpls_hdr(skb); dec = mpls_entry_decode(hdr); -- cgit v1.2.3-59-g8ed1b