netdev - Re: [PATCH net v2] skbuff: Fix skb checksum flag on skb pull

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Date:	Mon, 04 Jan 2016 22:04:40 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	pshelar@...ira.com, netdev@...r.kernel.org,
	willemdebruijn.kernel@...il.com
Subject: Re: [PATCH net v2] skbuff: Fix skb checksum flag on skb pull

On Mon, 2016-01-04 at 23:08 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 30 Dec 2015 13:05:45 -0500
> 
> > On Thu, 2015-09-24 at 14:09 -0700, David Miller wrote:
> >> From: Pravin B Shelar <pshelar@...ira.com>
> >> Date: Tue, 22 Sep 2015 12:57:53 -0700
> >> 
> >> > VXLAN device can receive skb with checksum partial. But the checksum
> >> > offset could be in outer header which is pulled on receive. This results
> >> > in negative checksum offset for the skb. Such skb can cause the assert
> >> > failure in skb_checksum_help(). Following patch fixes the bug by setting
> >> > checksum-none while pulling outer header.
> >> > 
> >> > Following is the kernel panic msg from old kernel hitting the bug.
> >>  ...
> >> > Reported-by: Anupam Chanda <achanda@...are.com>
> >> > Signed-off-by: Pravin B Shelar <pshelar@...ira.com>
> >> 
> >> Applied, thanks.
> > 
> > 
> > It looks like we also should clear skb->csum ?
> > 
> > __skb_checksum_complete() definitely would be confused by garbage in
> > skb->csum
> 
> Pravin, please take a look at this.

This might be ok :

Apparently users are supposed to init skb->csum in this case, as in 

udp4_csum_init()
-> skb_checksum_init_zero_check()
  -> __skb_checksum_validate()

-> __skb_checksum_validate_complete
   skb->csum = psum;




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