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. Use a standalone protocol variable and assign it accordingly to the header type Signed-off-by: Antonio Quartulli <[email protected]> --- gateway_client.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/gateway_client.c b/gateway_client.c index 973f02d..8ea13e1 100644 --- a/gateway_client.c +++ b/gateway_client.c @@ -626,23 +626,29 @@ bool batadv_gw_is_dhcp_target(struct sk_buff *skb, unsigned int *header_len) struct iphdr *iphdr; struct ipv6hdr *ipv6hdr; struct udphdr *udphdr; + uint16_t proto; /* check for ethernet header */ if (!pskb_may_pull(skb, *header_len + ETH_HLEN)) return false; ethhdr = (struct ethhdr *)skb->data; + proto = ntohs(ethhdr->h_proto); *header_len += ETH_HLEN; /* check for initial vlan header */ - if (ntohs(ethhdr->h_proto) == ETH_P_8021Q) { + if (proto == 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 = ntohs(vhdr->h_vlan_encapsulated_proto); *header_len += VLAN_HLEN; } /* check for ip header */ - switch (ntohs(ethhdr->h_proto)) { + switch (proto) { case ETH_P_IP: if (!pskb_may_pull(skb, *header_len + sizeof(*iphdr))) return false; @@ -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 == ETH_P_IP) && (ntohs(udphdr->dest) != 67)) return false; - if ((ntohs(ethhdr->h_proto) == ETH_P_IPV6) && + if ((proto == ETH_P_IPV6) && (ntohs(udphdr->dest) != 547)) return false; -- 1.8.1.5
