ongrep

commit 76234008a274c2d6d33e1e3f96afa6f93d110858
parent cadfe37f609d97ab2d77d78a0e90b70387477a32
Author: Stephen Gregoratto <dev@sgregoratto.me>
Date:   Wed, 16 Sep 2020 14:08:37 +1000

simplify packet offset math

- All possible inttypes used for calculating offsets changed to size_t.
- Stop doing pointer counting on void * in vlan_frame_count. This is
  illegal C.
- Better seperate variable declaration and setting in process.
- Axe ip_ver, switch on packet->ip_v instead.
- Reassign ip6_pkt if the datalink is an 802.11 radio. This makes sense,
  right?

Diffstat:
M
ngrep.c
 | 
41
+++++++++++++++++++++--------------------

1 file changed, 21 insertions(+), 20 deletions(-)
diff --git a/ngrep.c b/ngrep.c
@@ -93,7 +93,7 @@ dump_func	dumper = &dump_formatted;
 char		*filter = NULL;
 char		*filter_file = NULL;
 char		 pc_err[PCAP_ERRBUF_SIZE];
-uint8_t		 link_offset;
+size_t		 link_offset;
 bool		 radiotap_present = false;
 bool		 include_vlan = true;
 
@@ -597,14 +597,14 @@ setup_pattern_match(void)
 	return 0;
 }
 
-static inline uint8_t
-vlan_frame_count(u_char *p, uint16_t limit)
+static inline size_t
+vlan_frame_count(u_char *p, uint32_t caplen)
 {
-	uint8_t *et = (uint8_t *)(p + 12);
+	uint8_t *et = p + 12;
 	uint16_t ether_type = EXTRACT_16BITS(et);
-	uint8_t count = 0;
+	size_t count = 0;
 
-	while ((void *)et < (void *)(p + limit) &&
+	while (et < (p + caplen) &&
 	       ether_type != ETHERTYPE_IP &&
 	       ether_type != ETHERTYPE_IPV6) {
 		count++;
@@ -618,14 +618,11 @@ vlan_frame_count(u_char *p, uint16_t limit)
 void
 process(UNUSED u_char *d, struct pcap_pkthdr *h, u_char *p)
 {
-	uint8_t vlan_offset =
-	    include_vlan ? vlan_frame_count(p, h->caplen) * VLANHDR_SIZE : 0;
-
-	struct ip *ip4_pkt = (struct ip *)(p + link_offset + vlan_offset);
-	struct ip6_hdr *ip6_pkt =
-	    (struct ip6_hdr *)(p + link_offset + vlan_offset);
-
-	uint32_t ip_ver;
+	unsigned char *data;
+	struct ip *ip4_pkt;
+	struct ip6_hdr *ip6_pkt;
+	size_t vlan_offset = 0;
+	uint32_t len = 0;
 
 	uint8_t ip_proto = 0;
 	uint32_t ip_hl = 0;
@@ -638,21 +635,25 @@ process(UNUSED u_char *d, struct pcap_pkthdr *h, u_char *p)
 	char ip_src[INET6_ADDRSTRLEN + 1];
 	char ip_dst[INET6_ADDRSTRLEN + 1];
 
-	unsigned char *data;
-	uint32_t len = h->caplen - vlan_offset;
-
 	seen_frames++;
 
+	if (include_vlan)
+		vlan_offset = vlan_frame_count(p, h->caplen) * VLANHDR_SIZE;
+	len = h->caplen - vlan_offset;
+
+	ip4_pkt = (struct ip *)     (p + link_offset + vlan_offset);
+	ip6_pkt = (struct ip6_hdr *)(p + link_offset + vlan_offset);
+
 	if (radiotap_present) {
 		struct ieee80211_radiotap_header *rh =
 		    (struct ieee80211_radiotap_header*)p;
 		uint16_t radio_len = rh->it_len;
-		ip4_pkt = (struct ip *)(p + link_offset + radio_len);
+		ip4_pkt = (struct ip *)     (p + link_offset + radio_len);
+		ip6_pkt = (struct ip6_hdr *)(p + link_offset + radio_len);
 		len -= radio_len;
 	}
-	ip_ver = ip4_pkt->ip_v;
 
-	switch (ip_ver) {
+	switch (ip4_pkt->ip_v) {
 	case 4: {
 		ip_hl = ip4_pkt->ip_hl * 4;
 		ip_proto = ip4_pkt->ip_p;