netdev - Re: [PATCH v2] net-ipv6: fix excessive RTF_ADDRCONF flag on ::1/128 local route (and others)

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Message-ID: <98b8a95f-245a-0bdf-6a4c-c07a372d4d0f@gmail.com>
Date:   Thu, 5 Sep 2019 20:49:05 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Maciej Żenczykowski <zenczykowski@...il.com>,
        Maciej Żenczykowski <maze@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...il.com>,
        Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [PATCH v2] net-ipv6: fix excessive RTF_ADDRCONF flag on ::1/128
 local route (and others)



On 9/2/19 6:23 PM, Maciej Żenczykowski wrote:
> From: Maciej Żenczykowski <maze@...gle.com>
> 
> There is a subtle change in behaviour introduced by:
>   commit c7a1ce397adacaf5d4bb2eab0a738b5f80dc3e43
>   'ipv6: Change addrconf_f6i_alloc to use ip6_route_info_create'
> 
> Before that patch /proc/net/ipv6_route includes:
> 00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000003 00000000 80200001 lo
> 
> Afterwards /proc/net/ipv6_route includes:
> 00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80240001 lo
> 
> ie. the above commit causes the ::1/128 local (automatic) route to be flagged with RTF_ADDRCONF (0x040000).
> 
> AFAICT, this is incorrect since these routes are *not* coming from RA's.
> 
> As such, this patch restores the old behaviour.
> 
> Fixes: c7a1ce397adacaf5d4bb2eab0a738b5f80dc3e43
> Cc: David Ahern <dsahern@...il.com>
> Cc: Lorenzo Colitti <lorenzo@...gle.com>
> Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
> ---
>  net/ipv6/route.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 558c6c68855f..516b2e568dae 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -4365,13 +4365,14 @@ struct fib6_info *addrconf_f6i_alloc(struct net *net,
>  	struct fib6_config cfg = {
>  		.fc_table = l3mdev_fib_table(idev->dev) ? : RT6_TABLE_LOCAL,
>  		.fc_ifindex = idev->dev->ifindex,
> -		.fc_flags = RTF_UP | RTF_ADDRCONF | RTF_NONEXTHOP,
> +		.fc_flags = RTF_UP | RTF_NONEXTHOP,
>  		.fc_dst = *addr,
>  		.fc_dst_len = 128,
>  		.fc_protocol = RTPROT_KERNEL,
>  		.fc_nlinfo.nl_net = net,
>  		.fc_ignore_dev_down = true,
>  	};
> +	struct fib6_info *f6i;
>  
>  	if (anycast) {
>  		cfg.fc_type = RTN_ANYCAST;
> @@ -4381,7 +4382,10 @@ struct fib6_info *addrconf_f6i_alloc(struct net *net,
>  		cfg.fc_flags |= RTF_LOCAL;
>  	}
>  
> -	return ip6_route_info_create(&cfg, gfp_flags, NULL);
> +	f6i = ip6_route_info_create(&cfg, gfp_flags, NULL);
> +	if (f6i)
> +		f6i->dst_nocount = true;

Shouldn't it use 

	if (!IS_ERR(f6i))
		f6i->dst_nocount = true;

???


> +	return f6i;
>  }
>  
>  /* remove deleted ip from prefsrc entries */
>