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 <gna...@redhat.com>
---
include/net/dst.h | 12 +++++-------
net/mpls/af_mpls.c | 2 ++
2 files changed, 7 insertions(+), 7 deletions(-)
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;
}
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);
--
2.21.3
