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

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>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7e2e502ef51983fadd6956b0fdbf421b0c9aa1a6..5c3b906aeef3dc240a1ffd35a5493f9c4fcd2073 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5418,8 +5418,8 @@ 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;