linux-kernel - Re: [PATCH net v2] net/ipv6: Fix the RT cache flush via sysctl using a previous delay

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Date: Mon, 10 Jun 2024 09:26:34 -0600
From: David Ahern <dsahern@...nel.org>
To: Petr Pavlu <petr.pavlu@...e.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Kui-Feng Lee <thinker.li@...il.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net/ipv6: Fix the RT cache flush via sysctl using
 a previous delay

On 6/7/24 5:28 AM, Petr Pavlu wrote:
> The net.ipv6.route.flush system parameter takes a value which specifies
> a delay used during the flush operation for aging exception routes. The
> written value is however not used in the currently requested flush and
> instead utilized only in the next one.
> 
> A problem is that ipv6_sysctl_rtcache_flush() first reads the old value
> of net->ipv6.sysctl.flush_delay into a local delay variable and then
> calls proc_dointvec() which actually updates the sysctl based on the
> provided input.
> 
> Fix the problem by switching the order of the two operations.
> 
> Fixes: 4990509f19e8 ("[NETNS][IPV6]: Make sysctls route per namespace.")
> Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
> ---
> 
> Changes since v1 [1]:
> - Minimize the fix, correct only the order of operations in
>   ipv6_sysctl_rtcache_flush().
> 
> [1] https://lore.kernel.org/netdev/20240529135251.4074-1-petr.pavlu@suse.com/
> 
>  net/ipv6/route.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index f083d9faba6b..952c2bf11709 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -6343,12 +6343,12 @@ static int ipv6_sysctl_rtcache_flush(struct ctl_table *ctl, int write,
>  	if (!write)
>  		return -EINVAL;
>  
> -	net = (struct net *)ctl->extra1;
> -	delay = net->ipv6.sysctl.flush_delay;
>  	ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
>  	if (ret)
>  		return ret;
>  
> +	net = (struct net *)ctl->extra1;
> +	delay = net->ipv6.sysctl.flush_delay;
>  	fib6_run_gc(delay <= 0 ? 0 : (unsigned long)delay, net, delay > 0);
>  	return 0;
>  }
> 
> base-commit: 8a92980606e3585d72d510a03b59906e96755b8a


Reviewed-by: David Ahern <dsahern@...nel.org>