[PATCH 3.2 25/46] batman-adv: Check skb size before using encapsulated ETH+VLAN header

[Ben Hutchings <ben@decadent.org.uk>]

3.2.81-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sven Eckelmann <sven@narfation.org>

commit c78296665c3d81f040117432ab9e1cb125521b0c upstream.

The encapsulated ethernet and VLAN header may be outside the received
ethernet frame. Thus the skb buffer size has to be checked before it can be
parsed to find out if it encapsulates another batman-adv packet.

Fixes: 420193573f11 ("batman-adv: softif bridge loop avoidance")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/batman-adv/soft-interface.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -686,10 +686,16 @@ void interface_rx(struct net_device *sof
 	skb_pull_rcsum(skb, hdr_size);
 	skb_reset_mac_header(skb);
 
+	if (unlikely(!pskb_may_pull(skb, ETH_HLEN)))
+		goto dropped;
+
 	ethhdr = (struct ethhdr *)skb_mac_header(skb);
 
 	switch (ntohs(ethhdr->h_proto)) {
 	case ETH_P_8021Q:
+		if (!pskb_may_pull(skb, VLAN_ETH_HLEN))
+			goto dropped;
+
 		vhdr = (struct vlan_ethhdr *)skb->data;
 		vid = ntohs(vhdr->h_vlan_TCI) & VLAN_VID_MASK;
 
@@ -726,8 +732,6 @@ void interface_rx(struct net_device *sof
 	}
 
 	/* skb->dev & skb->pkt_type are set here */
-	if (unlikely(!pskb_may_pull(skb, ETH_HLEN)))
-		goto dropped;
 	skb->protocol = eth_type_trans(skb, soft_iface);
 
 	/* should not be necessary anymore as we use skb_pull_rcsum()