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Subject[PATCH 3.16.y-ckt 095/126] packet: fix match_fanout_group()
3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.


From: Eric Dumazet <>

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 <>
Cc: Willem de Bruijn <>
Cc: Eric Leblond <>
Signed-off-by: David S. Miller <>
Signed-off-by: Luis Henriques <>
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 e6bd6df9e2a2..1f618bbce0ac 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1412,10 +1412,10 @@ 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)

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