[PATCH net] net: neigh: guard against NULL solicit() method

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

Dmitry posted a nice reproducer of a bug triggering in neigh_probe()
when dereferencing a NULL neigh->ops->solicit method.

This can happen for arp_direct_ops/ndisc_direct_ops and similar,
which can be used for NUD_NOARP neighbours (created when dev->header_ops
is NULL). Admin can then force changing nud_state to some other state
that would fire neigh timer.

Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: Dmitry Vyukov <dvyu...@google.com>
---
 net/core/neighbour.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 
e7c12caa20c88acc9a5dd86f07d11644fb58341d..4526cbd7e28a1fcdecfc06a41985fd4d19634457
 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -860,7 +860,8 @@ static void neigh_probe(struct neighbour *neigh)
        if (skb)
                skb = skb_clone(skb, GFP_ATOMIC);
        write_unlock(&neigh->lock);
-       neigh->ops->solicit(neigh, skb);
+       if (neigh->ops->solicit)
+               neigh->ops->solicit(neigh, skb);
        atomic_inc(&neigh->probes);
        kfree_skb(skb);
 }