[B.A.T.M.A.N.] [PATCH maint 2/2] batman-adv: Avoid nullptr dereference in dat after vlan_insert_tag

[Sven Eckelmann <sven@narfation.org>]

vlan_insert_tag can return NULL on errors. The distributed arp table code
therefore has to check the return value of vlan_insert_tag for NULL before
it can safely operate on this pointer.

Fixes: 53c6c262a581 ("batman-adv: tag locally generated ARP reply if needed")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/distributed-arp-table.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index fa76465..b1cc8bf 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -1011,9 +1011,12 @@ bool batadv_dat_snoop_outgoing_arp_request(struct batadv_priv *bat_priv,
 		if (!skb_new)
 			goto out;
 
-		if (vid & BATADV_VLAN_HAS_TAG)
+		if (vid & BATADV_VLAN_HAS_TAG) {
 			skb_new = vlan_insert_tag(skb_new, htons(ETH_P_8021Q),
 						  vid & VLAN_VID_MASK);
+			if (!skb_new)
+				goto out;
+		}
 
 		skb_reset_mac_header(skb_new);
 		skb_new->protocol = eth_type_trans(skb_new,
@@ -1091,9 +1094,12 @@ bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
 	 */
 	skb_reset_mac_header(skb_new);
 
-	if (vid & BATADV_VLAN_HAS_TAG)
+	if (vid & BATADV_VLAN_HAS_TAG) {
 		skb_new = vlan_insert_tag(skb_new, htons(ETH_P_8021Q),
 					  vid & VLAN_VID_MASK);
+		if (!skb_new)
+			goto out;
+	}
 
 	/* To preserve backwards compatibility, the node has choose the outgoing
 	 * format based on the incoming request packet type. The assumption is
-- 
2.8.1