3 files changed, 196 insertions, 63 deletions

diff --git a/host.c b/host.c
new file mode 100644
index 0000000..b6e68dd
--- /dev/null
+++ b/host.c
@@ -0,0 +1,95 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <sys/types.h>
+#include <netdb.h>
+struct in_net {
+	struct in_addr addr;
+	struct in_addr mask;
+};
+/* not needed begin */
+#define POPCNT(y) int popcnt##x (uint##y##_t x) { \
+	int c = 0; \
+	for (int i = 0; i < y; i++) \
+		if (1 << i & x) \
+			c++; \
+	return c; \
+}
+POPCNT(32)
+unsigned int power2[] = { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648 }; /* ah yes, libmath */
+/* not needed end */
+struct in_addr host (struct in_net n, int h /* consecutive number of the host in the network */) {
+	n.addr.s_addr = ntohl(n.addr.s_addr & n.mask.s_addr);
+	n.mask.s_addr = ntohl(n.mask.s_addr);
+	int c = 1;
+	int s = 0;
+	for (int i = 0; i < 32; i++)
+		if (1 << i & ~n.mask.s_addr) {
+			if (1 << s++ & h)
+				n.addr.s_addr |= 1 << i;
+			c = c * 2;
+		}
+	if (h >= c)
+		n.addr.s_addr = 0;
+	n.addr.s_addr = htonl(n.addr.s_addr);
+	return n.addr;
+}
+int resolve (const char * d, uint32_t * r) {
+	struct addrinfo hints = {
+		.ai_family = AF_INET,
+		.ai_socktype = SOCK_DGRAM,
+		.ai_flags = 0,
+		.ai_protocol = 0,
+		.ai_canonname = NULL,
+		.ai_addr = NULL,
+		.ai_next = NULL
+	};
+	struct addrinfo * result;
+	int ret = getaddrinfo(d, NULL, &hints, &result);
+	*r = ((struct sockaddr_in *) result->ai_addr)->sin_addr.s_addr; /* ah yes, C */
+	freeaddrinfo(result);
+	return ret;
+}
+struct in_net str2net (char * s) { /* blocking, resolving */
+	struct in_net r = {
+		.mask = {
+			.s_addr = 0
+		},
+		.addr = {
+			.s_addr = 0
+		}
+	};
+	char * m = strchr(s, '/');
+	char o = '\0';
+	int e;
+	if (m) {
+		o = *m;
+		*m++ = '\0';
+	} else
+		m = "32";
+	fprintf(stderr, "str2net: resolving %s ... ", s);
+	if ((e = resolve(s, &r.addr.s_addr))) {
+		fprintf(stderr, "failed: %s\n", gai_strerror(e));
+		goto r;
+	}
+	fprintf(stderr, " %s mask %s ...", inet_ntoa(r.addr), m);
+	char * p;
+	int x = strtoll(m, &p, 10);
+	r.mask.s_addr = 0;
+	for (int j = 0; j < x && j < 32; j++)
+		r.mask.s_addr = r.mask.s_addr >> 1 | 1 << 31;
+	r.mask.s_addr = htonl(r.mask.s_addr);
+	if (*p)
+		if ((e = resolve(m, &r.mask.s_addr))) {
+			fprintf(stderr, "no: %s\n", gai_strerror(e));
+			goto r;
+		}
+	fprintf(stderr, " %s\n", inet_ntoa(r.mask));
+r:
+	if (o)
+		*--m = o;
+	return r;
+}
diff --git a/host_test.c b/host_test.c
new file mode 100644
index 0000000..0584686
--- /dev/null
+++ b/host_test.c
@@ -0,0 +1,9 @@
+#include "host.c"
+int main (int argc, char ** argv) {
+	if (argc != 3) {
+		fprintf(stderr, "%s network hostnumber\n", argv[0]);
+		return 1;
+	}
+	printf("%s\n", inet_ntoa(host(str2net(argv[1]), atoi(argv[2]))));
+	return 0;
+}
diff --git a/main.c b/main.c
index e490d7b..02ca7dd 100644
--- a/main.c
+++ b/main.c
@@ -13,20 +13,24 @@
 #include <netdb.h> /* getaddrinfo(3) */
 #include <stdlib.h> /* atoi(3) */
 #include <string.h> /* strchr(3) */
+#include <time.h> /* clock_gettime(2) */
 #include "domain2name.c"
+#include "host.c"
 #define MIN(a,b) ((a) < (b) ? (a) : (b))
 #define MAX(a,b) ((a) > (b) ? (a) : (b))
 #define MAXDOMAIN 255
 #define QUERYDOMAIN "http://sijanec.eu/link?r=.sijanec.eu."
 #define	EXPECTEDA 93.103.235.126
+#define XSTR(x) #x
+#define STR(x) XSTR(x)
 #define HELP "find recursive DNS resolvers on IPv4 networks\n" \
 	"%s [-a ipv4] [-b ipv4] [-d domain] [-h] [-o filename] [-p port] network1 [network2 ...]\n" \
 	"	-a Specify the IPv4 of the -d domain to be used instead of getaddrinfo(3).\n" \
 	"	-b Bind on a specific interface, defined by IPv4. Default is any interface.\n" \
 	"	-d Specify the domain name to be used in queries that has a single A record.\n" \
 	"	-h Show this help and exit.\n" \
-	"	-o Output PCAP to filename. Any existing file is truncated.\n" \
-	"	-p Set the source port number to use instead of a dynamically asigned one\n" \
+	"	-o Output PCAP to filename. Any existing file is truncated. No IP/UDP checksums.\n" \
+	"	-p Set the source port number to use instead of a dynamically asigned one.\n" \
 	"Network addresses are optionally followed by slash and netmask, otherwise networks are\n" \
 	"understood as single host addresses. Both network names and netmasks can be domains to\n" \
 	"be looked up or IP dot-notation addresses. Mask can also be a bit prefix (/32 default).\n" \
@@ -105,10 +109,16 @@ HEADER:
 		Option byte zero denotes an end of options, NOOP is option number 1
 	PADDING variable: zero bytes ensuring header is aligned into 32 bit words
 */
+/* UDP PACKET: HEADER DATA					https://www.ietf.org/rfc/rfc768.txt
+	SRCPORT	16 bits
+	DSTPORT	16 bits
+	LENGTH	16 bits: size of packet including header in bytes
+	CHCKSUM	16 bits: same algo as IP, data: pseudoheader (srcip dstip 0x0011 LENGTH) header data
+*/
 #define MICROSECOND 0xA1B2C3D4
 #define NANOSECOND 0xA1B23C4D
-#define PCAPVERMAJ 2
-#define PCAPVERMIN 4
+#define PCAPMAJ 2
+#define PCAPMIN 4
 enum linktype {
 	Ethernet = 1,
 	Ip = 101
@@ -153,25 +163,25 @@ enum ip_flags {
 	Mf = 1 << 2
 };
 enum protocol {
-	ICMP = 1,
-	TCP = 6,
-	UDP = 17
+	Icmp = 1,
+	Tcp = 6,
+	Udp = 17
 };
 struct ip {
 	unsigned int version : 4	__attribute__((packed));
-	unsigned int headlen : 4	__attribute__((packed));
-	enum precedence precedence : 3	__attribute__((packed));
+	unsigned int headlen : 4	__attribute__((packed)); /* measured in 32 bit words */
+	enum precedence precedence : 3	__attribute__((packed)); /* without optionts it's min 5 */
 	enum srvtype srvtype : 5	__attribute__((packed));
-	uint16_t length			__attribute__((packed));
+	uint16_t length			__attribute__((packed)); /* header + data in 8 bit words */
 	uint16_t identifier		__attribute__((packed));
 	enum ip_flags flags : 3		__attribute__((packed));
-	unsigned int foffset : 13	__attribute__((packed));
+	unsigned int foffset : 13	__attribute__((packed)); /* fragment offset - 64 bit words */
 	uint8_t ttl			/* ignored for uint8_t */;
 	enum protocol protocol : 8	__attribute__((packed));
 	uint16_t checksum		__attribute__((packed));
 	struct in_addr src		__attribute__((packed));
-	struct in_addr dst		__attribute__((packed));
-	char options[]			/* ignored for char[] */; /* options, padding and data */
+	struct in_addr dst		__attribute__((packed)); /* ----------- 20 bytes */
+	char options[]			/* ignored for char[] */;
 } __attribute__((packed));
 enum qr {
 	Question,
@@ -246,25 +256,55 @@ struct answer {
 	uint16_t rdlen			__attribute__((packed));
 	char * rdata			__attribute__((packed));
 };
-struct in_net {
-	struct in_addr addr;
-	struct in_addr mask;
+struct udp {
+	struct sockaddr_in src;
+	struct sockaddr_in dst;
+	size_t len; /* of data only */
+	char * data;
 };
-int resolve (const char * d, uint32_t * r) {
-	struct addrinfo hints = {
-		.ai_family = AF_INET,
-		.ai_socktype = SOCK_DGRAM,
-		.ai_flags = 0,
-		.ai_protocol = 0,
-		.ai_canonname = NULL,
-		.ai_addr = NULL,
-		.ai_next = NULL
+int logudp (int o /* file descriptor */, struct udp u) {
+	struct timespec t;
+	if (clock_gettime(CLOCK_REALTIME, &t) == -1) {
+		perror("clock_gettime(CLOCK_REALTIME, &t)");
+		return -1;
+	}
+	struct pcap_packet p = {
+		.seconds = t.tv_sec,
+		.subseconds = t.tv_nsec,
+		.capture_length = u.len,
+		.original_length = u.len
+	};
+	struct ip i = {
+		.version = 4,
+		.headlen = 5,
+		.precedence = Routine,
+		.srvtype = 0,
+		.length = htons(8+u.len),
+		.identifier = 0x6969,
+		.flags = 0,
+		.foffset = 0,
+		.ttl = 69,
+		.protocol = Udp,
+		.checksum = 0, /* wireshark does not validate, at least not on debian 11 */
+		.src = u.src.sin_addr,
+		.dst = u.dst.sin_addr
 	};
-	struct addrinfo * result;
-	int ret = getaddrinfo(d, NULL, &hints, &result);
-      	*r = ((struct sockaddr_in *) result->ai_addr)->sin_addr.s_addr; /* ah yes, C */
-	freeaddrinfo(result);
-	return ret;
+#define LOGUDP_L (sizeof p + sizeof i + 4*2 + u.len)
+	char * c, * b = alloca(LOGUDP_L); /* to do in one write (thread safe) */
+	char * n = "\0"; /* as per udp rfc when no checksum was calculated (-: */
+	uint16_t l = htons(u.len);
+	c = (char *) memcpy(b, &p, sizeof p) + sizeof p;
+	c = (char *) memcpy(c, &i, sizeof i) + sizeof i;
+	c = (char *) memcpy(c, &u.src.sin_port, 2) + 2;
+	c = (char *) memcpy(c, &u.dst.sin_port, 2) + 2;
+	c = (char *) memcpy(c, &l, 2) + 2;
+	c = (char *) memcpy(c, &n, 2) + 2;
+	c = (char *) memcpy(c, u.data, u.len) + u.len;
+	if (write(o, b, LOGUDP_L) == -1) { /* atomic and thread safe, as per posix */
+		perror("write(" STR(LOGUDP_L) ")");
+		return -2;
+	}
+	return 0;
 }
 int main (int argc, char ** argv) {
 	int r = 0;
@@ -306,7 +346,21 @@ int main (int argc, char ** argv) {
 					r = 1;
 					goto r;
 				}
-				write(o, "", 1);
+				struct pcap_global g = {
+					.subsecond = NANOSECOND,
+					.major = PCAPMAJ,
+					.minor = PCAPMIN,
+					.reserved[0] = 0,
+					.reserved[1] = 0,
+					.snaplen = 65535,
+					.fcs = 0,
+					.linktype = Ip
+				};
+				if (write(o, &g, sizeof g) == -1) {
+					perror("write(o, &g, sizeof g)");
+					r = 2;
+					goto r;
+				}
 				break;
 			case 'p':
 				b.sin_port = htons(atoi(optarg));
@@ -314,47 +368,22 @@ int main (int argc, char ** argv) {
 			case -1:
 				if (!(l = argc-optind)) {
 					fprintf(stderr, "specify targets to scan :: " HELP, argv[0]);
-					r = 2;
+					r = 3;
 					goto r;
 				}
 				n = alloca(l*sizeof(*n));
 				for (int i = optind; i < argc; i++) {
 					int w = i-optind;
-					char * m = strchr(argv[i], '/');
-					int e;
-					if (m)
-						*m++ = '\0';
-					else
-						m = "32";
-					fprintf(stderr, "network %d: resolving %s ... ", w, argv[i]);
-					if ((e = resolve(argv[i], &n[w].addr.s_addr))) {
-						fprintf(stderr, "failed: %s\n", gai_strerror(e));
-						r = 3;
-						goto r;
-					}
-					fprintf(stderr, " %s mask %s ...", inet_ntoa(n[w].addr), m);
-					char * p;
-					int x = strtoll(m, &p, 10);
-					n[w].mask.s_addr = 0;
-					for (int j = 0; j < x && j < 32; j++)
-						n[w].mask.s_addr = n[w].mask.s_addr >> 1 | 1 << 31;
-					n[w].mask.s_addr = htonl(n[w].mask.s_addr);
-					if (*p)
-						if ((e = resolve(m, &n[w].mask.s_addr))) {
-							fprintf(stderr, "no: %s\n", gai_strerror(e));
-							r = 4;
-							goto r;
-						}
-					fprintf(stderr, " %s\n", inet_ntoa(n[w].mask));
+					n[w] = str2net(argv[i]);
 				}
 				goto o;
 			case '?':
 				fprintf(stderr, "unknown option :: " HELP, argv[0]);
-				r = 5;
+				r = 6;
 				goto r;
 			case ':':
 				fprintf(stderr, "missing option argument :: " HELP, argv[0]);
-				r = 6;
+				r = 7;
 				goto r;
 		}
 	}
@@ -364,7 +393,7 @@ o:
 		fprintf(stderr, "resolving %s ... ", d);
 		if ((e = resolve(d, &a.s_addr))) {
 			fprintf(stderr, "failed: %s\n", gai_strerror(e));
-			r = 7;
+			r = 8;
 			goto r;
 		}
 		fprintf(stderr, " %s\n", inet_ntoa(a));
@@ -376,12 +405,12 @@ o:
 	}
 	if (bind(s, (struct sockaddr *) &b, sizeof(struct sockaddr))) {
 		perror("bind(s, (struct sokaddr *) &b, sizeof(struct sockaddr))");
-		r = 9;
+		r = 10;
 		goto r;
 	}
 	if ((c = fork()) == -1) {
 		perror("fork()");
-		r = 10;
+		r = 11;
 		goto r;
 	}
 r: