linux-kernel - [PATCH 5.8 02/16] net: Fix potential wrong skb->protocol in skb_vlan

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Message-Id: <20200826114911.339700140@linuxfoundation.org>
Date:   Wed, 26 Aug 2020 14:02:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miaohe Lin <linmiaohe@...wei.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.8 02/16] net: Fix potential wrong skb->protocol in skb_vlan_untag()

From: Miaohe Lin <linmiaohe@...wei.com>

[ 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@...wei.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/skbuff.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5419,8 +5419,8 @@ struct sk_buff *skb_vlan_untag(struct sk
 	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;