net: Fix potential wrong skb->protocol in skb_vlan_untag()

[ Upstream commit 55eff0eb7460c3d50716ed9eccf22257b046ca92 ]

We may access the two bytes after vlan_hdr in vlan_set_encap_proto(). So
we should pull VLAN_HLEN + sizeof(unsigned short) in skb_vlan_untag() or
we may access the wrong data.

Fixes: 0d5501c1c828 ("net: Always untag vlan-tagged traffic on input.")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7e29590482ce509ea1d3b2306f4796f697b76d4f..115f3fde314f3178618c4c871b2725b6300ef283 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5421,8 +5421,8 @@ struct sk_buff *skb_vlan_untag(struct sk_buff *skb)
        skb = skb_share_check(skb, GFP_ATOMIC);
        if (unlikely(!skb))
                goto err_free;
-
-       if (unlikely(!pskb_may_pull(skb, VLAN_HLEN)))
+       /* We may access the two bytes after vlan_hdr in vlan_set_encap_proto(). */
+       if (unlikely(!pskb_may_pull(skb, VLAN_HLEN + sizeof(unsigned short))))
                goto err_free;
 
        vhdr = (struct vlan_hdr *)skb->data;