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

[Daniel Borkmann]

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.

Fixes: 93515d53b133 ("net: move vlan pop/push functions into common code")
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
---
 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