Commit 008ba2a1 authored Sep 14, 2017 by Willem de Bruijn Committed by David S. Miller Sep 20, 2017

packet: hold bind lock when rebinding to fanout hook



Packet socket bind operations must hold the po->bind_lock. This keeps
po->running consistent with whether the socket is actually on a ptype
list to receive packets.

fanout_add unbinds a socket and its packet_rcv/tpacket_rcv call, then
binds the fanout object to receive through packet_rcv_fanout.

Make it hold the po->bind_lock when testing po->running and rebinding.
Else, it can race with other rebind operations, such as that in
packet_set_ring from packet_rcv to tpacket_rcv. Concurrent updates
can result in a socket being added to a fanout group twice, causing
use-after-free KASAN bug reports, among others.

Reported independently by both trinity and syzkaller.
Verified that the syzkaller reproducer passes after this patch.

Fixes: dc99f600 ("packet: Add fanout support.")
Reported-by: nixioaming <nixiaoming@huawei.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 35e015e1

net/packet/af_packet.c

+11 −5

Original line number	Diff line number	Diff line
		@@ -1684,10 +1684,6 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)

		mutex_lock(&fanout_mutex);

		err = -EINVAL;
		if (!po->running)
		goto out;

		err = -EALREADY;
		if (po->fanout)
		goto out;
		@@ -1749,7 +1745,10 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
		list_add(&match->list, &fanout_list);
		}
		err = -EINVAL;
		if (match->type == type &&

		spin_lock(&po->bind_lock);
		if (po->running &&
		match->type == type &&
		match->prot_hook.type == po->prot_hook.type &&
		match->prot_hook.dev == po->prot_hook.dev) {
		err = -ENOSPC;
		@@ -1761,6 +1760,13 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
		err = 0;
		}
		}
		spin_unlock(&po->bind_lock);

		if (err && !refcount_read(&match->sk_ref)) {
		list_del(&match->list);
		kfree(match);
		}

		out:
		if (err && rollover) {
		kfree(rollover);

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