netdev - Issue in __vlan_put

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Message-Id: <F1E039CF-14E4-4200-8AF3-EBB62ECC6519@nicira.com>
Date:	Fri, 12 Oct 2007 16:58:17 -0700
From:	Justin Pettit <jpettit@...ira.com>
To:	netdev@...r.kernel.org
Subject: Issue in __vlan_put_tag?

The function __vlan_put_tag modifies adds a VLAN tag to an existing  
Ethernet packet.  In the process, the front of the packet is extended  
by four bytes to accommodate the tag.  This function correctly  
adjusts the mac_header offset, but I think this line is problematic:

	skb->network_header -= VLAN_HLEN;

When access to the network header is needed, the value of skb- 
 >network_header is added to skb->head, which should not have changed  
during any of the previous modifications.  I believe the code as it  
exists now will cause the network header to appear to be four bytes  
earlier than it actually is.

--Justin
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