packet: fix match_fanout_group()

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@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Eric Leblond <eric@regit.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 20c44e2e1e4e1e813a937a75d8f65a880324867f..396b3f1e7cc0371b74abc40c34b77e76cd4e772f 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1519,10 +1519,10 @@ 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 void fanout_init_data(struct packet_fanout *f)