netdev - Re: kernel >= 4.0: crashes when using traceroute6 with isatap

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Message-ID: <1460179.Gl6yCv4mQ9@h2o.as.studentenwerk.mhn.de>
Date:	Thu, 14 May 2015 02:32:24 +0200
From:	Wolfgang Walter <linux@...m.de>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: kernel >= 4.0: crashes when using traceroute6 with isatap

Am Dienstag, 12. Mai 2015, 16:18:54 schrieb Vlad Yasevich:
> On 05/06/2015 06:11 PM, Wolfgang Walter wrote:
> > Am Mittwoch, 6. Mai 2015, 11:15:18 schrieben Sie:
> >> (Cc'ing netdev.)
> >> 
> >> On Sat, May 2, 2015 at 5:29 AM, Wolfgang Walter <linux@...m.de> wrote:
> >>> Am Samstag, 2. Mai 2015, 02:16:36 schrieb Wolfgang Walter:
> >>>> Hello,
> >>>> 
> >>>> kernel 4.0 (and 4.0.1) crashes immediately when I use traceroute6 with
> >>>> an
> >>>> isatap-tunnel.
> >>> 
> >>> I did some further tests. To trigger the crash you need
> >>> 
> >>> * isatap-tunnel (probably any sit-tunnel will do it)
> >>> * raw-socket
> >>> * udp
> >>> 
> >>> Using icmpv6 or tcp i.e. does not trigger it.
> >> 
> >> Do you have a script to reproduce it?
> >> 
> >> 
> >> Thanks for the bug report!
> > 
> > You need a isatap-server with say ipv4-address $X
> > 
> > Then, on host with 4.0, start isatapd: isatapd --mtu 1280 $X
> > 
> > then do
> > 
> > 	traceroute6 www.google.de
> > 
> > Regards,
> 
> Hi Walter
> 
> Could you try this patch.  Looks like raw passes transhdrlen
> of 0 on the first packet and that makes IPv4 behave correctly,
> but not IPv6.
> 
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 7fde1f2..fd9c079 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1278,7 +1278,7 @@ emsgsize:
>  	/* If this is the first and only packet and device
>  	 * supports checksum offloading, let's use it.
>  	 */
> -	if (!skb && sk->sk_protocol == IPPROTO_UDP &&
> +	if (transhdrlen && sk->sk_protocol == IPPROTO_UDP &&
>  	    length + fragheaderlen < mtu &&
>  	    rt->dst.dev->features & NETIF_F_V6_CSUM &&
>  	    !exthdrlen)

Ok, that works as fix. No crash and checksums are ok.

Regards,
-- 
Wolfgang Walter
Studentenwerk München
Anstalt des öffentlichen Rechts
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