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packet: in packet_do_bind, test fanout with bind_lock held

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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: dc99f60069 ("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>
This commit is contained in:
Willem de Bruijn 2017-09-26 12:19:37 -04:00 committed by David S. Miller
parent 1579f678fb
commit 4971613c16
1 changed files with 5 additions and 3 deletions
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8
net/packet/af_packet.c
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@ -3069,13 +3069,15 @@ 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) {