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

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Date:   Thu, 23 Mar 2017 12:39:21 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     edumazet@...gle.com, dvyukov@...gle.com, xiyou.wangcong@...il.com,
        herbert@...dor.apana.org.au, ast@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com
Subject: [PATCH net] net: neigh: guard against NULL solicit() method

From: Eric Dumazet <edumazet@...gle.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 <edumazet@...gle.com>
Reported-by: Dmitry Vyukov <dvyukov@...gle.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);
 }