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

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Date:	Wed, 30 Dec 2015 13:05:45 -0500
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	pshelar@...ira.com, netdev@...r.kernel.org,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net v2] skbuff: Fix skb checksum flag on skb pull

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

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6b6bd42d6134..43e6f6163e07 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2799,8 +2799,10 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
 	if (skb->ip_summed == CHECKSUM_COMPLETE)
 		skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
 	else if (skb->ip_summed == CHECKSUM_PARTIAL &&
-		 skb_checksum_start_offset(skb) < 0)
+		 skb_checksum_start_offset(skb) < 0) {
 		skb->ip_summed = CHECKSUM_NONE;
+		skb->csum = 0;
+	}
 }
 
 unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);



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