Re: [PATCH net] packet: in packet_do_bind, test fanout with bind_lock held

[David Miller]

From: Willem de Bruijn 
Date: Tue, 26 Sep 2017 12:19:37 -0400

> From: Willem de Bruijn 
> 
> 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 
> Reviewed-by: Eric Dumazet 

Applied and queued up for -stable.

[PATCH net] packet: in packet_do_bind, test fanout with bind_lock held

[Willem de Bruijn]

From: Willem de Bruijn 

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 
Reviewed-by: Eric Dumazet 
---
 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 1da0851f51f2..bec01a3daf5b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3071,13 +3071,15 @@ 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) {
-- 
2.14.1.821.g8fa685d3b7-goog