netdev - Re: [PATCH net-next] ipv6: guard ip6_mr

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Message-ID: <740387fb-ed72-4a6f-9625-c4fccb1f09ab@blackwall.org>
Date: Fri, 27 Jun 2025 16:33:35 +0300
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>,
 David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
 eric.dumazet@...il.com,
 syzbot+0141c834e47059395621@...kaller.appspotmail.com,
 Petr Machata <petrm@...dia.com>, Roopa Prabhu <roopa@...dia.com>,
 Benjamin Poirier <bpoirier@...dia.com>, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next] ipv6: guard ip6_mr_output() with rcu

On 6/27/25 14:58, Eric Dumazet wrote:
> syzbot found at least one path leads to an ip_mr_output()
> without RCU being held.
> 
> Add guard(rcu)() to fix this in a concise way.
> 
> WARNING: net/ipv6/ip6mr.c:2376 at ip6_mr_output+0xe0b/0x1040 net/ipv6/ip6mr.c:2376, CPU#1: kworker/1:2/121
> Call Trace:
>  <TASK>
>   ip6tunnel_xmit include/net/ip6_tunnel.h:162 [inline]
>   udp_tunnel6_xmit_skb+0x640/0xad0 net/ipv6/ip6_udp_tunnel.c:112
>   send6+0x5ac/0x8d0 drivers/net/wireguard/socket.c:152
>   wg_socket_send_skb_to_peer+0x111/0x1d0 drivers/net/wireguard/socket.c:178
>   wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
>   wg_packet_tx_worker+0x1c8/0x7c0 drivers/net/wireguard/send.c:276
>   process_one_work kernel/workqueue.c:3239 [inline]
>   process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3322
>   worker_thread+0x8a0/0xda0 kernel/workqueue.c:3403
>   kthread+0x70e/0x8a0 kernel/kthread.c:464
>   ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> 
> Fixes: 96e8f5a9fe2d ("net: ipv6: Add ip6_mr_output()")
> Reported-by: syzbot+0141c834e47059395621@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/685e86b3.a00a0220.129264.0003.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Petr Machata <petrm@...dia.com>
> Cc: Roopa Prabhu <roopa@...dia.com>
> Cc: Nikolay Aleksandrov <razor@...ckwall.org>
> Cc: Benjamin Poirier <bpoirier@...dia.com>
> Cc: Ido Schimmel <idosch@...dia.com>
> ---
>  net/ipv6/ip6mr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index a35f4f1c658960e4b087848461f3ea7af653d070..eb6a00262510f1cd6a9d48fab80bdd0d496bb7ee 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -2373,7 +2373,7 @@ int ip6_mr_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  	int err;
>  	int vif;
>  
> -	WARN_ON_ONCE(!rcu_read_lock_held());
> +	guard(rcu)();
>  
>  	if (IP6CB(skb)->flags & IP6SKB_FORWARDED)
>  		goto ip6_output;

Thanks,
Reviewed-by: Nikolay Aleksandrov <razor@...ckwall.org>