ctdb-common: Clarify offset and packet length calculations

Calculate each offset from the beginning of the buffer and explicitly
use the sizes of structures.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

diff --git a/ctdb/common/system_socket.c b/ctdb/common/system_socket.c
index a6c5f5c093df331f20249614c74b47f2d838b826..b528b89af8fbab7dac600d2cec45f978a7e3dd22 100644 (file)
--- a/ctdb/common/system_socket.c
+++ b/ctdb/common/system_socket.c
@@ -216,12 +216,12 @@ static int arp_build(uint8_t *buffer,
        memcpy(eh->ether_shost, hwaddr, ETH_ALEN);
        eh->ether_type = htons(ETHERTYPE_ARP);
 
-       ea = (struct ether_arp *)&buffer[sizeof(struct ether_header)];
+       ea = (struct ether_arp *)(buffer + sizeof(struct ether_header));
        ah = &ea->ea_hdr;
        ah->ar_hrd = htons(ARPHRD_ETHER);
        ah->ar_pro = htons(ETH_P_IP);
        ah->ar_hln = ETH_ALEN;
-       ah->ar_pln = 4;
+       ah->ar_pln = sizeof(ea->arp_spa);
 
        if (! reply) {
                ah->ar_op  = htons(ARPOP_REQUEST);
@@ -277,9 +277,9 @@ static int ip6_na_build(uint8_t *buffer,
        memcpy(eh->ether_shost, hwaddr, ETH_ALEN);
        eh->ether_type = htons(ETHERTYPE_IP6);
 
-       ip6 = (struct ip6_hdr *)(eh+1);
+       ip6 = (struct ip6_hdr *)(buffer + sizeof(struct ether_header));
        ip6->ip6_vfc  = 0x60;
-       ip6->ip6_plen = htons(sizeof(*nd_na) +
+       ip6->ip6_plen = htons(sizeof(struct nd_neighbor_advert) +
                              sizeof(struct nd_opt_hdr) +
                              ETH_ALEN);
        ip6->ip6_nxt  = IPPROTO_ICMPV6;
@@ -292,17 +292,27 @@ static int ip6_na_build(uint8_t *buffer,
                return EIO;
        }
 
-       nd_na = (struct nd_neighbor_advert *)(ip6+1);
+       nd_na = (struct nd_neighbor_advert *)(buffer +
+                                             sizeof(struct ether_header) +
+                                             sizeof(struct ip6_hdr));
        nd_na->nd_na_type = ND_NEIGHBOR_ADVERT;
        nd_na->nd_na_code = 0;
        nd_na->nd_na_flags_reserved = ND_NA_FLAG_OVERRIDE;
        nd_na->nd_na_target = addr->sin6_addr;
+
        /* Option: Target link-layer address */
-       nd_oh = (struct nd_opt_hdr *)(nd_na+1);
+       nd_oh = (struct nd_opt_hdr *)(buffer +
+                                     sizeof(struct ether_header) +
+                                     sizeof(struct ip6_hdr) +
+                                     sizeof(struct nd_neighbor_advert));
        nd_oh->nd_opt_type = ND_OPT_TARGET_LINKADDR;
-       nd_oh->nd_opt_len = 1;
+       nd_oh->nd_opt_len = 1;  /* multiple of 8 octets */
 
-       ea = (struct ether_addr *)(nd_oh+1);
+       ea = (struct ether_addr *)(buffer +
+                                  sizeof(struct ether_header) +
+                                  sizeof(struct ip6_hdr) +
+                                  sizeof(struct nd_neighbor_advert) +
+                                  sizeof(struct nd_opt_hdr));
        memcpy(ea, hwaddr, ETH_ALEN);
 
        nd_na->nd_na_cksum = ip6_checksum((uint16_t *)nd_na,