In the gateway code in case of 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.

This trick is correct but the code is not easy to understand and may lead to bugs in case of re-use of ethhdr for other purposes.

Do some code refactoring in order to make it easier to understand and to change in the future.

Signed-off-by: Antonio Quartulli ordex@autistici.org ---

v2: - slightly change the commit subject and message - use __constant_htons() when comparing proto with constants

gateway_client.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/gateway_client.c b/gateway_client.c index 973f02d..f59e58d 100644 --- a/gateway_client.c +++ b/gateway_client.c @@ -626,24 +626,30 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len) struct iphdr *iphdr; struct ipv6hdr *ipv6hdr; struct udphdr *udphdr; + __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 == __constant_htons(ETH_P_8021Q)) { + struct vlan_ethhdr *vhdr; + 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 __constant_htons(ETH_P_IP): if (!pskb_may_pull(skb, *header_len + sizeof(*iphdr))) return false; iphdr = (struct iphdr *)(skb->data + *header_len); @@ -654,7 +660,7 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len) return false;

break; - case ETH_P_IPV6: + case __constant_htons(ETH_P_IPV6): if (!pskb_may_pull(skb, *header_len + sizeof(*ipv6hdr))) return false; ipv6hdr = (struct ipv6hdr *)(skb->data + *header_len); @@ -675,11 +681,11 @@ 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 == __constant_htons(ETH_P_IP)) && (ntohs(udphdr->dest) != 67)) return false;

- if ((ntohs(ethhdr->h_proto) == ETH_P_IPV6) && + if ((proto == __constant_htons(ETH_P_IPV6)) && (ntohs(udphdr->dest) != 547)) return false;