Patch "vlan: Fix untag operations of stacked vlans with REORDER_HEADER off" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

vlan: Fix untag operations of stacked vlans with REORDER_HEADER off

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
vlan-fix-untag-operations-of-stacked-vlans-with-reorder_header-off.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Vlad Yasevich <[email protected]>
Date: Mon, 16 Nov 2015 15:43:44 -0500
Subject: vlan: Fix untag operations of stacked vlans with REORDER_HEADER off

From: Vlad Yasevich <[email protected]>

[ Upstream commit a6e18ff111701b4ff6947605bfbe9594ec42a6e8 ]

When we have multiple stacked vlan devices all of which have turned off REORDER_HEADER flag, the untag operation does not locate the ethernet addresses correctly for nested vlans. The reason is that in case of REORDER_HEADER flag being off, the outer vlan headers are put back and the mac_len is adjusted to account for the presense of the header. Then, the subsequent untag operation, for the next level vlan, always use VLAN_ETH_HLEN to locate the begining of the ethernet header and that ends up being a multiple of 4 bytes short of the actuall beginning of the mac header (the multiple depending on the how many vlan encapsulations ethere are).

As a reslult, if there are multiple levles of vlan devices with REODER_HEADER being off, the recevied packets end up being dropped.

To solve this, we use skb->mac_len as the offset. The value is always set on receive path and starts out as a ETH_HLEN. The value is also updated when the vlan header manupations occur so we know it will be correct.

---
 net/core/skbuff.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -4200,7 +4200,8 @@ static struct sk_buff *skb_reorder_vlan_
 		return NULL;
 	}
 
-	memmove(skb->data - ETH_HLEN, skb->data - VLAN_ETH_HLEN, 2 * ETH_ALEN);
+	memmove(skb->data - ETH_HLEN, skb->data - skb->mac_len,
+		2 * ETH_ALEN);
 	skb->mac_header += VLAN_HLEN;
 	return skb;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/ipv6-sctp-clone-options-to-avoid-use-after-free.patch queue-4.1/skbuff-fix-offset-error-in-skb_reorder_vlan_header.patch queue-4.1/sctp-update-the-netstamp_needed-counter-when-copying-sockets.patch queue-4.1/sctp-also-copy-sk_tsflags-when-copying-the-socket.patch queue-4.1/sctp-use-the-same-clock-as-if-sock-source-timestamps-were-on.patch queue-4.1/vlan-fix-untag-operations-of-stacked-vlans-with-reorder_header-off.patch