netdev - Re: [PATCH RFC 1/2] ipv6: Fix after pmtu events dissapearing host routes

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Message-ID: <20150205235628.GA1916791@devbig242.prn2.facebook.com>
Date:	Thu, 5 Feb 2015 15:56:29 -0800
From:	Martin Lau <kafai@...com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
CC:	Yang Yingliang <yangyingliang@...wei.com>,
	netdev <netdev@...r.kernel.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH RFC 1/2] ipv6: Fix after pmtu events dissapearing host
 routes

On Wed, Jan 28, 2015 at 01:11:51PM +0100, Steffen Klassert wrote:
> We currently don't clone host routes before we use them.
> If a pmtu event is received on such a route, it gets
> an expires value. As soon as the expiration time is
> elapsed, the route is deleted. As a result, the host
> is not reachable any more.
> 
> We fix this by cloning host routes if they are gatewayed,
> i.e. if pmtu events can happen.
> 
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
>  net/ipv6/route.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index c910831..3e864e7 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -961,7 +961,7 @@ redo_rt6_select:
>  
>  	if (!(rt->rt6i_flags & (RTF_NONEXTHOP | RTF_GATEWAY)))
>  		nrt = rt6_alloc_cow(rt, &fl6->daddr, &fl6->saddr);
> -	else if (!(rt->dst.flags & DST_HOST))
> +	else if (!(rt->dst.flags & DST_HOST) || (rt->rt6i_flags & RTF_GATEWAY))
>  		nrt = rt6_alloc_clone(rt, &fl6->daddr);
The del path may also require changes.  I am thinking:
1. Create a /128 via gateway route
2. Send some traffic and RTF_CACHE rt is created
3. Delete the /128 route by ip route del.  I suspect the RTF_CACHE route may be
   deleted and the route added in (1) stays.

Thanks
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