netdev - [PATCH net] xfrm: fix a data-race in xfrm_lookup_with

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Date: Wed, 11 Oct 2023 10:24:29 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, syzbot <syzkaller@...glegroups.com>, 
	Steffen Klassert <steffen.klassert@...unet.com>
Subject: [PATCH net] xfrm: fix a data-race in xfrm_lookup_with_ifid()

syzbot complains about a race in xfrm_lookup_with_ifid() [1]

When preparing commit 0a9e5794b21e ("xfrm: annotate data-race
around use_time") I thought xfrm_lookup_with_ifid() was modifying
a still private structure.

[1]
BUG: KCSAN: data-race in xfrm_lookup_with_ifid / xfrm_lookup_with_ifid

write to 0xffff88813ea41108 of 8 bytes by task 8150 on cpu 1:
xfrm_lookup_with_ifid+0xce7/0x12d0 net/xfrm/xfrm_policy.c:3218
xfrm_lookup net/xfrm/xfrm_policy.c:3270 [inline]
xfrm_lookup_route+0x3b/0x100 net/xfrm/xfrm_policy.c:3281
ip6_dst_lookup_flow+0x98/0xc0 net/ipv6/ip6_output.c:1246
send6+0x241/0x3c0 drivers/net/wireguard/socket.c:139
wg_socket_send_skb_to_peer+0xbd/0x130 drivers/net/wireguard/socket.c:178
wg_socket_send_buffer_to_peer+0xd6/0x100 drivers/net/wireguard/socket.c:200
wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
wg_packet_handshake_send_worker+0x10c/0x150 drivers/net/wireguard/send.c:51
process_one_work kernel/workqueue.c:2630 [inline]
process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2703
worker_thread+0x525/0x730 kernel/workqueue.c:2784
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:304

write to 0xffff88813ea41108 of 8 bytes by task 15867 on cpu 0:
xfrm_lookup_with_ifid+0xce7/0x12d0 net/xfrm/xfrm_policy.c:3218
xfrm_lookup net/xfrm/xfrm_policy.c:3270 [inline]
xfrm_lookup_route+0x3b/0x100 net/xfrm/xfrm_policy.c:3281
ip6_dst_lookup_flow+0x98/0xc0 net/ipv6/ip6_output.c:1246
send6+0x241/0x3c0 drivers/net/wireguard/socket.c:139
wg_socket_send_skb_to_peer+0xbd/0x130 drivers/net/wireguard/socket.c:178
wg_socket_send_buffer_to_peer+0xd6/0x100 drivers/net/wireguard/socket.c:200
wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
wg_packet_handshake_send_worker+0x10c/0x150 drivers/net/wireguard/send.c:51
process_one_work kernel/workqueue.c:2630 [inline]
process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2703
worker_thread+0x525/0x730 kernel/workqueue.c:2784
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:304

value changed: 0x00000000651cd9d1 -> 0x00000000651cd9d2

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15867 Comm: kworker/u4:58 Not tainted 6.6.0-rc4-syzkaller-00016-g5e62ed3b1c8a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
Workqueue: wg-kex-wg2 wg_packet_handshake_send_worker

Fixes: 0a9e5794b21e ("xfrm: annotate data-race around use_time")
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Steffen Klassert <steffen.klassert@...unet.com>
---
 net/xfrm/xfrm_policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index a73e4b66c98f9db98d94a146bc963fa29979c592..1058530d2a7235abe0f051e26695efbfc84feb33 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3213,7 +3213,7 @@ struct dst_entry *xfrm_lookup_with_ifid(struct net *net,
 	}
 
 	for (i = 0; i < num_pols; i++)
-		pols[i]->curlft.use_time = ktime_get_real_seconds();
+		WRITE_ONCE(pols[i]->curlft.use_time, ktime_get_real_seconds());
 
 	if (num_xfrms < 0) {
 		/* Prohibit the flow */
-- 
2.42.0.609.gbb76f46606-goog