Re: [PATCH net] wireguard: receive: annotate data-race around receiving_counter.counter

[Eric Dumazet]

On Thu, Jan 11, 2024 at 4:41 PM Nikita Zhandarovich
<n.zhandarovich@xxxxxxxxxx> wrote:
>
> Syzkaller with KCSAN identified a data-race issue [1] when accessing
> keypair->receiving_counter.counter.
>
> This patch uses READ_ONCE() and WRITE_ONCE() annotations to fix the
> problem.
>
> [1]
> BUG: KCSAN: data-race in wg_packet_decrypt_worker / wg_packet_rx_poll
>
> write to 0xffff888107765888 of 8 bytes by interrupt on cpu 0:
>  counter_validate drivers/net/wireguard/receive.c:321 [inline]
>  wg_packet_rx_poll+0x3ac/0xf00 drivers/net/wireguard/receive.c:461
>  __napi_poll+0x60/0x3b0 net/core/dev.c:6536
>  napi_poll net/core/dev.c:6605 [inline]
>  net_rx_action+0x32b/0x750 net/core/dev.c:6738
>  __do_softirq+0xc4/0x279 kernel/softirq.c:553
>  do_softirq+0x5e/0x90 kernel/softirq.c:454
>  __local_bh_enable_ip+0x64/0x70 kernel/softirq.c:381
>  __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
>  _raw_spin_unlock_bh+0x36/0x40 kernel/locking/spinlock.c:210
>  spin_unlock_bh include/linux/spinlock.h:396 [inline]
>  ptr_ring_consume_bh include/linux/ptr_ring.h:367 [inline]
>  wg_packet_decrypt_worker+0x6c5/0x700 drivers/net/wireguard/receive.c:499
>  process_one_work kernel/workqueue.c:2633 [inline]
>  ...
>
> read to 0xffff888107765888 of 8 bytes by task 3196 on cpu 1:
>  decrypt_packet drivers/net/wireguard/receive.c:252 [inline]
>  wg_packet_decrypt_worker+0x220/0x700 drivers/net/wireguard/receive.c:501
>  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
>  ...
>
> Fixes: a9e90d9931f3 ("wireguard: noise: separate receive counter from send counter")
> Reported-by: syzbot+d1de830e4ecdaac83d89@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
> ---
>  drivers/net/wireguard/receive.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
> index a176653c8861..d91383afb6e2 100644
> --- a/drivers/net/wireguard/receive.c
> +++ b/drivers/net/wireguard/receive.c
> @@ -251,7 +251,7 @@ static bool decrypt_packet(struct sk_buff *skb, struct noise_keypair *keypair)
>
>         if (unlikely(!READ_ONCE(keypair->receiving.is_valid) ||
>                   wg_birthdate_has_expired(keypair->receiving.birthdate, REJECT_AFTER_TIME) ||
> -                 keypair->receiving_counter.counter >= REJECT_AFTER_MESSAGES)) {
> +                 READ_ONCE(keypair->receiving_counter.counter) >= REJECT_AFTER_MESSAGES)) {
>                 WRITE_ONCE(keypair->receiving.is_valid, false);
>                 return false;
>         }
> @@ -318,7 +318,7 @@ static bool counter_validate(struct noise_replay_counter *counter, u64 their_cou
>                 for (i = 1; i <= top; ++i)
>                         counter->backtrack[(i + index_current) &
>                                 ((COUNTER_BITS_TOTAL / BITS_PER_LONG) - 1)] = 0;
> -               counter->counter = their_counter;
> +               WRITE_ONCE(counter->counter, their_counter);
>         }
>
>         index &= (COUNTER_BITS_TOTAL / BITS_PER_LONG) - 1;

It seems you forgot to add this as well ?

diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
index a176653c88616b1bc871fe52fcea778b5e189f69..a1493c94cea042165f8523a4dac573800a6d03c4
100644
--- a/drivers/net/wireguard/receive.c
+++ b/drivers/net/wireguard/receive.c
@@ -463,7 +463,7 @@ int wg_packet_rx_poll(struct napi_struct *napi, int budget)
                        net_dbg_ratelimited("%s: Packet has invalid
nonce %llu (max %llu)\n",
                                            peer->device->dev->name,
                                            PACKET_CB(skb)->nonce,
-                                           keypair->receiving_counter.counter);
+
READ_ONCE(keypair->receiving_counter.counter));
                        goto next;
                }

Thanks.