netdev - Re: [PATCH net-next] net: fix possible wrong checksum generation

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Message-ID: <CALnjE+o_oHB9aoJApkjut=iJ0uHCHGQMguyeP0WNmTgUZgrQEg@mail.gmail.com>
Date:	Tue, 29 Jan 2013 11:30:10 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	jesse@...ira.com
Subject: Re: [PATCH net-next] net: fix possible wrong checksum generation

On Mon, Jan 28, 2013 at 10:35 AM, Ben Hutchings
<bhutchings@...arflare.com> wrote:
> On Fri, 2013-01-25 at 22:34 -0800, Eric Dumazet wrote:
>> From: Eric Dumazet <edumazet@...gle.com>
>>
>> Pravin Shelar mentioned that GSO could potentially generate
>> wrong TX checksum if skb has fragments that are overwritten
>> by the user between the checksum computation and transmit.
>>
>> He suggested to linearize skbs but this extra copy can be
>> avoided for normal tcp skbs cooked by tcp_sendmsg().
>>
>> This patch introduces a new SKB_GSO_SHARED_FRAG flag, set
>> in skb_shinfo(skb)->gso_type if at least one frag can be
>> modified by the user.
> [...]
>
> Again, this needs a net device feature, doesn't it?  net_gso_ok() should
> allow hardware checksum/segmentation offload of such packets, and it
> won't if there is this new GSO flag with no corresponding net device
> feature.
>

I am not sure if this flag need to be a GSO type. There is possibility
of having such a page fragment in non GSO packets.
we could have this flag in skb_shinfo(skb)->tx_flags.

Thanks,
Pravin.
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