linux-kernel - [PATCH 3.10 253/268] net: neigh: guard against NULL solicit() method

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Date:   Mon, 19 Jun 2017 20:32:32 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 253/268] net: neigh: guard against NULL solicit() method

From: Eric Dumazet <edumazet@...gle.com>

commit 48481c8fa16410ffa45939b13b6c53c2ca609e5f upstream.

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Willy Tarreau <w@....eu>
---
 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 b49e8ba..fb82e8a 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -872,7 +872,8 @@ static void neigh_probe(struct neighbour *neigh)
 	if (skb)
 		skb = skb_copy(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);
 }
-- 
2.8.0.rc2.1.gbe9624a