batman-adv: h_vlan_encapsulated_proto access refactoring

In case of a VLAN tagged frame the ethhdr pointer is
moved forward by 4 bytes so that the offset of h_proto
in struct ethhdr matches the real
h_vlan_encapsulated_proto address in the skb. While this
trickery is correct it makes the code harder to understand
and may lead to bugs in case of re-use of ethhdr for other
purposes.

This patch introduces a proto variable to make things
cleaner and easier to understand.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>

1 files changed, 12 insertions, 7 deletions

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index 1bce63aa5f5f..ac97ca7f4ad0 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -655,24 +655,29 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
         struct iphdr *iphdr;
         struct ipv6hdr *ipv6hdr;
         struct udphdr *udphdr;
+        struct vlan_ethhdr *vhdr;
+        __be16 proto;
 
         /* check for ethernet header */
         if (!pskb_may_pull(skb, *header_len + ETH_HLEN))
                 return false;
         ethhdr = (struct ethhdr *)skb->data;
+        proto = ethhdr->h_proto;
         *header_len += ETH_HLEN;
 
         /* check for initial vlan header */
-        if (ntohs(ethhdr->h_proto) == ETH_P_8021Q) {
+        if (proto == htons(ETH_P_8021Q)) {
                 if (!pskb_may_pull(skb, *header_len + VLAN_HLEN))
                         return false;
-                ethhdr = (struct ethhdr *)(skb->data + VLAN_HLEN);
+
+                vhdr = (struct vlan_ethhdr *)skb->data;
+                proto = vhdr->h_vlan_encapsulated_proto;
                 *header_len += VLAN_HLEN;
         }
 
         /* check for ip header */
-        switch (ntohs(ethhdr->h_proto)) {
-        case ETH_P_IP:
+        switch (proto) {
+        case htons(ETH_P_IP):
                 if (!pskb_may_pull(skb, *header_len + sizeof(*iphdr)))
                         return false;
                 iphdr = (struct iphdr *)(skb->data + *header_len);
@@ -683,7 +688,7 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
                         return false;
 
                 break;
-        case ETH_P_IPV6:
+        case htons(ETH_P_IPV6):
                 if (!pskb_may_pull(skb, *header_len + sizeof(*ipv6hdr)))
                         return false;
                 ipv6hdr = (struct ipv6hdr *)(skb->data + *header_len);
@@ -710,11 +715,11 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len)
         *header_len += sizeof(*udphdr);
 
         /* check for bootp port */
-        if ((ntohs(ethhdr->h_proto) == ETH_P_IP) &&
+        if ((proto == htons(ETH_P_IP)) &&
             (ntohs(udphdr->dest) != 67))
                 return false;
 
-        if ((ntohs(ethhdr->h_proto) == ETH_P_IPV6) &&
+        if ((proto == htons(ETH_P_IPV6)) &&
             (ntohs(udphdr->dest) != 547))
                 return false;