netdev - Re: [PATCH net] ipv4: fib: annotate races around nh->nh_saddr_genid and nh->nh

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Message-ID: <20231018134900.GO1940501@kernel.org>
Date: Wed, 18 Oct 2023 15:49:00 +0200
From: Simon Horman <horms@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
	eric.dumazet@...il.com, syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] ipv4: fib: annotate races around nh->nh_saddr_genid
 and nh->nh_saddr

On Tue, Oct 17, 2023 at 07:23:04PM +0000, Eric Dumazet wrote:
> syzbot reported a data-race while accessing nh->nh_saddr_genid [1]
> 
> Add annotations, but leave the code lazy as intended.
> 
> [1]
> BUG: KCSAN: data-race in fib_select_path / fib_select_path
> 
> write to 0xffff8881387166f0 of 4 bytes by task 6778 on cpu 1:
> fib_info_update_nhc_saddr net/ipv4/fib_semantics.c:1334 [inline]
> fib_result_prefsrc net/ipv4/fib_semantics.c:1354 [inline]
> fib_select_path+0x292/0x330 net/ipv4/fib_semantics.c:2269
> ip_route_output_key_hash_rcu+0x659/0x12c0 net/ipv4/route.c:2810
> ip_route_output_key_hash net/ipv4/route.c:2644 [inline]
> __ip_route_output_key include/net/route.h:134 [inline]
> ip_route_output_flow+0xa6/0x150 net/ipv4/route.c:2872
> send4+0x1f5/0x520 drivers/net/wireguard/socket.c:61
> wg_socket_send_skb_to_peer+0x94/0x130 drivers/net/wireguard/socket.c:175
> 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
> 
> read to 0xffff8881387166f0 of 4 bytes by task 6759 on cpu 0:
> fib_result_prefsrc net/ipv4/fib_semantics.c:1350 [inline]
> fib_select_path+0x1cb/0x330 net/ipv4/fib_semantics.c:2269
> ip_route_output_key_hash_rcu+0x659/0x12c0 net/ipv4/route.c:2810
> ip_route_output_key_hash net/ipv4/route.c:2644 [inline]
> __ip_route_output_key include/net/route.h:134 [inline]
> ip_route_output_flow+0xa6/0x150 net/ipv4/route.c:2872
> send4+0x1f5/0x520 drivers/net/wireguard/socket.c:61
> wg_socket_send_skb_to_peer+0x94/0x130 drivers/net/wireguard/socket.c:175
> 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: 0x959d3217 -> 0x959d3218
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 6759 Comm: kworker/u4:15 Not tainted 6.6.0-rc4-syzkaller-00029-gcbf3a2cb156a #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
> Workqueue: wg-kex-wg1 wg_packet_handshake_send_worker
> 
> Fixes: 436c3b66ec98 ("ipv4: Invalidate nexthop cache nh_saddr more correctly.")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Simon Horman <horms@...nel.org>