net: neigh: guard against NULL solicit() method

BugLink: http://bugs.launchpad.net/bugs/1688499
[ Upstream commit 48481c8fa16410ffa45939b13b6c53c2ca609e5f ]

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 <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index e7c12caa20c88acc9a5dd86f07d11644fb58341d..4526cbd7e28a1fcdecfc06a41985fd4d19634457 100644 (file)
--- 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);
 }