Commit 4971613c authored Sep 26, 2017 by Willem de Bruijn Committed by David S. Miller Sep 28, 2017

packet: in packet_do_bind, test fanout with bind_lock held



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: dc99f600 ("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>

parent 1579f678

net/packet/af_packet.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -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) {

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