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 --- include/net/dst.h | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'include/net/dst.h') diff --git a/include/net/dst.h b/include/net/dst.h index 8ea8812b0b41..10f0a8399867 100644 --- a/include/net/dst.h +++ b/include/net/dst.h @@ -400,14 +400,12 @@ static inline struct neighbour *dst_neigh_lookup(const struct dst_entry *dst, co static inline struct neighbour *dst_neigh_lookup_skb(const struct dst_entry *dst, struct sk_buff *skb) { - struct neighbour *n = NULL; + struct neighbour *n; - /* The packets from tunnel devices (eg bareudp) may have only - * metadata in the dst pointer of skb. Hence a pointer check of - * neigh_lookup is needed. - */ - if (dst->ops->neigh_lookup) - n = dst->ops->neigh_lookup(dst, skb, NULL); + if (WARN_ON_ONCE(!dst->ops->neigh_lookup)) + return NULL; + + n = dst->ops->neigh_lookup(dst, skb, NULL); return IS_ERR(n) ? NULL : n; } -- cgit v1.2.3