linux-kernel - Re: [PATCH net v3] xfrm: fix ip_rt_bug race in icmp_route

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Message-ID: <62b51184-cc76-42cc-beea-91b6e815132f@kernel.org>
Date: Thu, 5 Feb 2026 08:17:18 -0700
From: David Ahern <dsahern@...nel.org>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>, netdev@...r.kernel.org
Cc: Jiayuan Chen <jiayuan.chen@...pee.com>,
 syzbot+e738404dcd14b620923c@...kaller.appspotmail.com,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, Herbert Xu <herbert@...dor.apana.org.au>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v3] xfrm: fix ip_rt_bug race in icmp_route_lookup
 reverse path

On 2/5/26 12:02 AM, Jiayuan Chen wrote:
> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> index 4abbec2f47ef..35816ac749bc 100644
> --- a/net/ipv4/icmp.c
> +++ b/net/ipv4/icmp.c
> @@ -554,6 +554,22 @@ static struct rtable *icmp_route_lookup(struct net *net, struct flowi4 *fl4,
>  		/* steal dst entry from skb_in, don't drop refcnt */
>  		skb_dstref_steal(skb_in);
>  		skb_dstref_restore(skb_in, orefdst);
> +
> +		/*
> +		 * At this point, fl4_dec.daddr should NOT be local (we
> +		 * checked fl4_dec.saddr above). However, a race condition
> +		 * may occur if the address is added to the interface
> +		 * concurrently. In that case, ip_route_input() returns a
> +		 * LOCAL route with dst.output=ip_rt_bug, which must not
> +		 * be used for output.
> +		 */
> +		if (!err && rt2 && rt2->rt_type == RTN_LOCAL) {
> +			net_warn_ratelimited("detected local route for %pI4 "
> +					     "during ICMP sending, src %pI4\n",
> +					     &fl4_dec.daddr, &fl4_dec.saddr);

per Paolo comment on the previous revision of this patch, strings should
not be split across lines like this. It should be:

net_warn_ratelimited("detected local route for %pI4 during ICMP sending,
src %pI4\n",

> +			dst_release(&rt2->dst);
> +			err = -EINVAL;
> +		}
>  	}
>  
>  	if (err)