netdev - [PATCH] net: Fix potential wrong skb->protocol in skb_vlan

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Date:   Sat, 15 Aug 2020 04:44:31 -0400
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>, <pshelar@....org>,
        <fw@...len.de>, <martin.varghese@...ia.com>, <edumazet@...gle.com>,
        <dcaratti@...hat.com>, <steffen.klassert@...unet.com>,
        <pabeni@...hat.com>, <shmulik@...anetworks.com>,
        <kyk.segfault@...il.com>, <jiri@...lanox.com>,
        <vyasevic@...hat.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH] 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@...wei.com>
---
 net/core/skbuff.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7e2e502ef519..5c3b906aeef3 100644
--- 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;
-- 
2.19.1