netdev - Re: [PATCH] ipv6: address issue in __ip6_append

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Message-ID: <20150221183359.GB16874@kria>
Date:	Sat, 21 Feb 2015 19:33:59 +0100
From:	Sabrina Dubroca <sd@...asysnail.net>
To:	Madalin Bucur <madalin.bucur@...escale.com>
Cc:	netdev@...r.kernel.org, vyasevich@...il.com, davem@...emloft.net
Subject: Re: [PATCH] ipv6: address issue in __ip6_append_data

2015-02-13, 17:30:59 +0200, Madalin Bucur wrote:
> Hello,
> 
> I think I've found a problem that allows generic IPv6 traffic to be
> sent by the stack with CHECKSUM_PARTIAL to a netdevice that declares
> NETIF_F_IPV6_CSUM. The NETIF_F_IPV6_CSUM flag is based on the
> NETIF_F_IPV6_CSUM_BIT that is described as referring only to TCP and
> UDP but in my test ICMPv6 frames with CHECKSUM_PARTIAL are seen:

This should be fixed by:

    bf250a1fa769 ("ipv6: Partial checksum only UDP packets")

Have you tested it?


> NETIF_F_IPV6_CSUM_BIT,          /* Can checksum TCP/UDP over IPV6 */
> 
> I've traced the issue to a recent commit that includes this check:
> 
> 	rt->dst.dev->features & NETIF_F_V6_CSUM
> 
> The problem with this is that NETIF_F_V6_CSUM is more than one bit:
> 
> #define NETIF_F_V6_CSUM         (NETIF_F_GEN_CSUM | NETIF_F_IPV6_CSUM)
> 
> Thus the above check should be either:
> 
> 	(rt->dst.dev->features & NETIF_F_V6_CSUM) == NETIF_F_V6_CSUM

I think this disables HW checksumming that Vlad's patch enabled.  As
Vlad pointed out in another similar thread [1], the two bits are
mutually exclusive, so you can't have

    (dev->features & NETIF_F_V6_CSUM) == NETIF_F_V6_CSUM

[1] http://www.spinics.net/lists/netdev/msg316341.html


> or probably should use NETIF_F_HW_CSUM only:
> 
> 	rt->dst.dev->features & NETIF_F_HW_CSUM

Maybe.  But I just tried this, and it doesn't work with qemu's e1000
emulation (could be a driver/qemu problem, I can't check with other
devices).


Thanks,
-- 
Sabrina
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