[PATCH 3.2 09/52] packet: fix match_fanout_group()

[Ben Hutchings]

3.2.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit 161642e24fee40fba2c5bc2ceacc00d118a22d65 upstream.

Recent TCP listener patches exposed a prior af_packet bug :
match_fanout_group() blindly assumes it is always safe
to cast sk to a packet socket to compare fanout with af_packet_priv

But SYNACK packets can be sent while attached to request_sock, which
are smaller than a "struct sock".

We can read non existent memory and crash.

Fixes: c0de08d04215 ("af_packet: don't emit packet on orig fanout group")
Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
Cc: Eric Leblond <eric@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/packet/af_packet.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1263,10 +1263,10 @@ static void __fanout_unlink(struct sock
 
 bool match_fanout_group(struct packet_type *ptype, struct sock * sk)
 {
-	if (ptype->af_packet_priv == (void*)((struct packet_sock *)sk)->fanout)
-		return true;
+	if (sk->sk_family != PF_PACKET)
+		return false;
 
-	return false;
+	return ptype->af_packet_priv == pkt_sk(sk)->fanout;
 }
 
 static int fanout_add(struct sock *sk, u16 id, u16 type_flags)

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