[PATCH 3.19.y-ckt 160/164] packet: fix match_fanout_group()

[Kamal Mostafa]

3.19.8-ckt11 -stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet at google.com>

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 at google.com>
Cc: Willem de Bruijn <willemb at google.com>
Cc: Eric Leblond <eric at regit.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/packet/af_packet.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index bfc1880..ca5c040 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1405,10 +1405,10 @@ static void __fanout_unlink(struct sock *sk, struct packet_sock *po)
 
 static 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)
-- 
1.9.1