linux-kernel - [PATCH 4.1 28/43] vlan: Fix untag operations of stacked vlans with REORDER

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Message-Id: <20160120215931.037460209@linuxfoundation.org>
Date:	Wed, 20 Jan 2016 15:10:35 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Vladislav Yasevich <vyasevic@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.1 28/43] vlan: Fix untag operations of stacked vlans with REORDER_HEADER off

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vlad Yasevich <vyasevich@...il.com>

[ 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.

Signed-off-by: Vladislav Yasevich <vyasevic@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/skbuff.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -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;
 }