batman-adv: fix potential kernel paging errors for unicast transmissions

index e14531f..264de88 100644
@@ -1529,6 +1529,8 @@ out:
  * in these cases, the skb is further handled by this function and
  * returns 1, otherwise it returns 0 and the caller shall further
  * process the skb.
+ *
+ * This call might reallocate skb data.
  */
 int batadv_bla_tx(struct batadv_priv *bat_priv, struct sk_buff *skb,
 		  unsigned short vid)

index f105219..e1516d5 100644
@@ -508,6 +508,7 @@ out:
 	return 0;
 }
 
+/* this call might reallocate skb data */
 static bool batadv_is_type_dhcprequest(struct sk_buff *skb, int header_len)
 {
 	int ret = false;

@@ -568,6 +569,7 @@ out:
 	return ret;
 }
 
+/* this call might reallocate skb data */
 bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
 {
 	struct ethhdr *ethhdr;

@@ -619,6 +621,11 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
 
 	if (!pskb_may_pull(skb, *header_len + sizeof(*udphdr)))
 		return false;
+
+	ethhdr = (struct ethhdr *)skb->data;
+	if (ntohs(ethhdr->h_proto) == ETH_P_8021Q)
+		ethhdr = (struct ethhdr *)(skb->data + VLAN_HLEN);
+
 	udphdr = (struct udphdr *)(skb->data + *header_len);
 	*header_len += sizeof(*udphdr);
 

@@ -634,12 +641,14 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
 	return true;
 }
 
+/* this call might reallocate skb data */
 bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
-			    struct sk_buff *skb, struct ethhdr *ethhdr)
+			    struct sk_buff *skb)
 {
 	struct batadv_neigh_node *neigh_curr = NULL, *neigh_old = NULL;
 	struct batadv_orig_node *orig_dst_node = NULL;
 	struct batadv_gw_node *curr_gw = NULL;
+	struct ethhdr *ethhdr;
 	bool ret, out_of_range = false;
 	unsigned int header_len = 0;
 	uint8_t curr_tq_avg;

@@ -648,6 +657,7 @@ bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
 	if (!ret)
 		goto out;
 
+	ethhdr = (struct ethhdr *)skb->data;
 	orig_dst_node = batadv_transtable_search(bat_priv, ethhdr->h_source,
 						 ethhdr->h_dest);
 	if (!orig_dst_node)

index 039902d..1037d75 100644
@@ -34,7 +34,6 @@ void batadv_gw_node_delete(struct batadv_priv *bat_priv,
 void batadv_gw_node_purge(struct batadv_priv *bat_priv);
 int batadv_gw_client_seq_print_text(struct seq_file *seq, void *offset);
 bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len);
-bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
-			    struct sk_buff *skb, struct ethhdr *ethhdr);
+bool batadv_gw_out_of_range(struct batadv_priv *bat_priv, struct sk_buff *skb);
 
 #endif /* _NET_BATMAN_ADV_GATEWAY_CLIENT_H_ */

index 700d0b4..b39e50d 100644
@@ -180,6 +180,8 @@ static int batadv_interface_tx(struct sk_buff *skb,
 	if (batadv_bla_tx(bat_priv, skb, vid))
 		goto dropped;
 
+	ethhdr = (struct ethhdr *)skb->data;
+
 	/* Register the client MAC in the transtable */
 	if (!is_multicast_ether_addr(ethhdr->h_source))
 		batadv_tt_local_add(soft_iface, ethhdr->h_source, skb->skb_iif);

@@ -220,6 +222,10 @@ static int batadv_interface_tx(struct sk_buff *skb,
 		default:
 			break;
 		}
+
+		/* reminder: ethhdr might have become unusable from here on
+		 * (batadv_gw_is_dhcp_target() might have reallocated skb data)
+		 */
 	}
 
 	/* ethernet packet should be broadcasted */

@@ -266,7 +272,7 @@ static int batadv_interface_tx(struct sk_buff *skb,
 	/* unicast packet */
 	} else {
 		if (atomic_read(&bat_priv->gw_mode) != BATADV_GW_MODE_OFF) {
-			ret = batadv_gw_out_of_range(bat_priv, skb, ethhdr);
+			ret = batadv_gw_out_of_range(bat_priv, skb);
 			if (ret)
 				goto dropped;
 		}

index 4c5a1aa..7250b10 100644
@@ -326,7 +326,9 @@ static bool batadv_unicast_push_and_fill_skb(struct sk_buff *skb, int hdr_size,
  * @skb: the skb containing the payload to encapsulate
  * @orig_node: the destination node
  *
- * Returns false if the payload could not be encapsulated or true otherwise
+ * Returns false if the payload could not be encapsulated or true otherwise.
+ *
+ * This call might reallocate skb data.
  */
 static bool batadv_unicast_prepare_skb(struct sk_buff *skb,
 				       struct batadv_orig_node *orig_node)

@@ -343,7 +345,9 @@ static bool batadv_unicast_prepare_skb(struct sk_buff *skb,
  * @orig_node: the destination node
  * @packet_subtype: the batman 4addr packet subtype to use
  *
- * Returns false if the payload could not be encapsulated or true otherwise
+ * Returns false if the payload could not be encapsulated or true otherwise.
+ *
+ * This call might reallocate skb data.
  */
 bool batadv_unicast_4addr_prepare_skb(struct batadv_priv *bat_priv,
 				      struct sk_buff *skb,

@@ -444,6 +448,7 @@ find_router:
 	}
 
 	unicast_packet = (struct batadv_unicast_packet *)skb->data;
+	ethhdr = (struct ethhdr *)skb->data;
 
 	/* inform the destination node that we are still missing a correct route
 	 * for this client. The destination will receive this packet and will