netdev - [PATCH net 4/4] wireguard: send: annotate intentional data race in checking empty queue

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Message-ID: <20240704154517.1572127-5-Jason@zx2c4.com>
Date: Thu,  4 Jul 2024 17:45:17 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: netdev@...r.kernel.org,
	davem@...emloft.net,
	kuba@...nel.org
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
	stable@...r.kernel.org
Subject: [PATCH net 4/4] wireguard: send: annotate intentional data race in checking empty queue

KCSAN reports a race in wg_packet_send_keepalive, which is intentional:

    BUG: KCSAN: data-race in wg_packet_send_keepalive / wg_packet_send_staged_packets

    write to 0xffff88814cd91280 of 8 bytes by task 3194 on cpu 0:
     __skb_queue_head_init include/linux/skbuff.h:2162 [inline]
     skb_queue_splice_init include/linux/skbuff.h:2248 [inline]
     wg_packet_send_staged_packets+0xe5/0xad0 drivers/net/wireguard/send.c:351
     wg_xmit+0x5b8/0x660 drivers/net/wireguard/device.c:218
     __netdev_start_xmit include/linux/netdevice.h:4940 [inline]
     netdev_start_xmit include/linux/netdevice.h:4954 [inline]
     xmit_one net/core/dev.c:3548 [inline]
     dev_hard_start_xmit+0x11b/0x3f0 net/core/dev.c:3564
     __dev_queue_xmit+0xeff/0x1d80 net/core/dev.c:4349
     dev_queue_xmit include/linux/netdevice.h:3134 [inline]
     neigh_connected_output+0x231/0x2a0 net/core/neighbour.c:1592
     neigh_output include/net/neighbour.h:542 [inline]
     ip6_finish_output2+0xa66/0xce0 net/ipv6/ip6_output.c:137
     ip6_finish_output+0x1a5/0x490 net/ipv6/ip6_output.c:222
     NF_HOOK_COND include/linux/netfilter.h:303 [inline]
     ip6_output+0xeb/0x220 net/ipv6/ip6_output.c:243
     dst_output include/net/dst.h:451 [inline]
     NF_HOOK include/linux/netfilter.h:314 [inline]
     ndisc_send_skb+0x4a2/0x670 net/ipv6/ndisc.c:509
     ndisc_send_rs+0x3ab/0x3e0 net/ipv6/ndisc.c:719
     addrconf_dad_completed+0x640/0x8e0 net/ipv6/addrconf.c:4295
     addrconf_dad_work+0x891/0xbc0
     process_one_work kernel/workqueue.c:2633 [inline]
     process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2706
     worker_thread+0x525/0x730 kernel/workqueue.c:2787
     kthread+0x1d7/0x210 kernel/kthread.c:388
     ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
     ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

    read to 0xffff88814cd91280 of 8 bytes by task 3202 on cpu 1:
     skb_queue_empty include/linux/skbuff.h:1798 [inline]
     wg_packet_send_keepalive+0x20/0x100 drivers/net/wireguard/send.c:225
     wg_receive_handshake_packet drivers/net/wireguard/receive.c:186 [inline]
     wg_packet_handshake_receive_worker+0x445/0x5e0 drivers/net/wireguard/receive.c:213
     process_one_work kernel/workqueue.c:2633 [inline]
     process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2706
     worker_thread+0x525/0x730 kernel/workqueue.c:2787
     kthread+0x1d7/0x210 kernel/kthread.c:388
     ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
     ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

    value changed: 0xffff888148fef200 -> 0xffff88814cd91280

Mark this race as intentional by using the skb_queue_empty_lockless()
function rather than skb_queue_empty(), which uses READ_ONCE()
internally to annotate the race.

Cc: stable@...r.kernel.org
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/net/wireguard/send.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c
index 0d48e0f4a1ba..26e09c30d596 100644
--- a/drivers/net/wireguard/send.c
+++ b/drivers/net/wireguard/send.c
@@ -222,7 +222,7 @@ void wg_packet_send_keepalive(struct wg_peer *peer)
 {
 	struct sk_buff *skb;
 
-	if (skb_queue_empty(&peer->staged_packet_queue)) {
+	if (skb_queue_empty_lockless(&peer->staged_packet_queue)) {
 		skb = alloc_skb(DATA_PACKET_HEAD_ROOM + MESSAGE_MINIMUM_LENGTH,
 				GFP_ATOMIC);
 		if (unlikely(!skb))
-- 
2.45.2