netdev - Re: [PATCH net] net/ipv6: fix incorrect fib6 gateway info after do redirect

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Message-ID: <2f7a40e2-9a72-a1fc-61f0-eb38e6487a72@gmail.com>
Date:   Thu, 6 Sep 2018 08:35:08 -0600
From:   David Ahern <dsahern@...il.com>
To:     Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net] net/ipv6: fix incorrect fib6 gateway info after do
 redirect

On 9/6/18 6:57 AM, Hangbin Liu wrote:
> When receive a redirect message and call rt6_do_redirect(), we allocate
> a new rt6_info and set new flags and gateway info, but not update these
> info to fib6_info.
> 
> Then if a user try to get the route info via `ip route get`, he will still
> get the old default gateway, because inet6_rtm_getroute() get gateway info
> from fib6_info.
> 
> Fixes: 23fb93a4d3f11 ("net/ipv6: Cleanup exception and cache route handling")
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
>  net/ipv6/route.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 18e00ce..3d367c9 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -3446,6 +3446,10 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu
>  		goto out;
>  	}
>  
> +	/* Update fib6_info from rt6_info */
> +	from->fib6_flags = rt->rt6i_flags;
> +	from->fib6_nh.nh_gw = rt->rt6i_gateway;
> +
>  	netevent.old = &rt->dst;
>  	netevent.new = &nrt->dst;
>  	netevent.daddr = &msg->dest;
> 

Only an exception should be inserted - and it is. The original route
should not be updated.

The code prior to the fib6_info did not update the actual FIB entry, and
the IPv4 code does not update the original route.