From: Willem de Bruijn <willemb@google.com>
Date: Tue, 26 Sep 2017 12:19:37 -0400
Subject: packet: in packet_do_bind, test fanout with bind_lock held
Patch-mainline: v4.14-rc4
Git-commit: 4971613c1639d8e5f102c4e797c3bf8f83a5a69e
References: CVE-2017-15649 bsc#1064388
Once a socket has po->fanout set, it remains a member of the group
until it is destroyed. The prot_hook must be constant and identical
across sockets in the group.
If fanout_add races with packet_do_bind between the test of po->fanout
and taking the lock, the bind call may make type or dev inconsistent
with that of the fanout group.
Hold po->bind_lock when testing po->fanout to avoid this race.
I had to introduce artificial delay (local_bh_enable) to actually
observe the race.
Fixes: dc99f600698d ("packet: Add fanout support.")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>
---
net/packet/af_packet.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e18d8cfe7af2..23c4653ef0f0 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3076,13 +3076,15 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
int ret = 0;
bool unlisted = false;
- if (po->fanout)
- return -EINVAL;
-
lock_sock(sk);
spin_lock(&po->bind_lock);
rcu_read_lock();
+ if (po->fanout) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
if (name) {
dev = dev_get_by_name_rcu(sock_net(sk), name);
if (!dev) {
--
2.14.2