netdev - [PATCH net v2] vlan: pull on __vlan_insert_tag error path and fix csum correction

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Message-Id: <bde2d4bf994b57e3ca25960d4b347212c8077ac6.1460765959.git.daniel@iogearbox.net>
Date:	Sat, 16 Apr 2016 02:27:58 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	davem@...emloft.net
Cc:	jiri@...nulli.us, netdev@...r.kernel.org,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH net v2] vlan: pull on __vlan_insert_tag error path and fix csum correction

When __vlan_insert_tag() fails from skb_vlan_push() path due to the
skb_cow_head(), we need to undo the __skb_push() in the error path
as well that was done earlier to move skb->data pointer to mac header.

Moreover, I noticed that when in the non-error path the __skb_pull()
is done and the original offset to mac header was non-zero, we fixup
from a wrong skb->data offset in the checksum complete processing.

So the skb_postpush_rcsum() really needs to be done before __skb_pull()
where skb->data still points to the mac header start and thus operates
under the same conditions as in __vlan_insert_tag().

Fixes: 93515d53b133 ("net: move vlan pop/push functions into common code")
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Reviewed-by: Jiri Pirko <jiri@...lanox.com>
---
 v1 -> v2:
   - Resend/code still the same, Jiri gave it a review as well meanwhile.

 net/core/skbuff.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d04c2d1..e561f9f 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4502,13 +4502,16 @@ int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
 		__skb_push(skb, offset);
 		err = __vlan_insert_tag(skb, skb->vlan_proto,
 					skb_vlan_tag_get(skb));
-		if (err)
+		if (err) {
+			__skb_pull(skb, offset);
 			return err;
+		}
+
 		skb->protocol = skb->vlan_proto;
 		skb->mac_len += VLAN_HLEN;
-		__skb_pull(skb, offset);

 		skb_postpush_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
+		__skb_pull(skb, offset);
 	}
 	__vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
 	return 0;
-- 
1.9.3