path: root/main.c

#include <sys/socket.h> /* udp(7) */
#include <netinet/in.h>
#include <netinet/udp.h>
#include <poll.h> /* poll(2) */
#include <sys/types.h> /* socket(2) */
#include <sys/socket.h>
#include <unistd.h> /* close(2) */
#include <stdio.h> /* perror(3) */
#include <sys/stat.h> /* open(2) */
#include <fcntl.h>
#include <errno.h> /* errno(3) */
#include <arpa/inet.h> /* byteorder(3) */
#include <netdb.h> /* getaddrinfo(3) */
#include <stdlib.h> /* atoi(3) */
#include <string.h> /* strchr(3) */
#include <time.h> /* clock_gettime(2) */
#include <signal.h> /* signal(2) */
#include <sys/prctl.h> /* prctl(2) */
#include <sys/wait.h> /* waitpid(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 ip] [-b ip] [-d domain] [-h] [-o file] [-p port] [-t μs] [-w μs] net1 [net2 ...]\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. No IP/UDP checksums.\n" \
	"	-p Set the source port number to use instead of a dynamically asigned one.\n" \
	"	-t Number of microseconds to wait between sent packets. (default 1000 - 64 KB/s)\n" \
	"	-w Finish after μs after recv'd last packet when done sending. (default 1000000)\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" \
	"When scanning the Internet please make sure that you specify your own domain instead\n" \
	"of the default one (dnsfind.sijanec.eu).\n" \
	"It would take a day to scan the entire address space with the default timings.\n"
/* DNS PACKET: HEADER QUESTION ANSWER AUTHORITY ADDITIONAL 	datatracker.ietf.org/doc/html/rfc1035
DEFINITIONS: (those appear somewhere in the packet, packet does not start with definitions!)
	LABLEN	 8 bits: first two bits zero, then 6 bits length of label
	POINTER	 8 bits: first two bits one, then 6 bits as offset from first byte of packet
	STRING	a single byte for defining length (0-256 - all eight bits) and then string of chars
	DOMAIN	 i.) one or more LABLEN followed by ASCII label (no dots) end with either LABLEN 0
		or a POINTER that points to some LABLEN somewhere else in the packet		-OR-:
		ii.) a POINTER that points to some LABLEN somewhere else in the packet
HEADER:		12 bytes
	XID	16 bits: random string to be matched in response to prevent cache poisoning
     /	QR	 1 bit : what type is this packet?	0 quest	1 response
    |	OPCODE   4 bits: type of query			0 query	1 iquer	2 sstat	3-15 reserved
1 byte	AA	 1 bit : is response authoritative?	0 no	1 yes
    |	TC	 1 bit : was response truncated?	0 no	1 yes
     \	RD       1 bit : does query desire recursion?	0 no	1 yes
     /	RA	 1 bit : does response server recurse?	0 no	1 yes
1 byte	Z	 3 bits: reserved for future		0 only option
     \	RCODE	 4 bits: error condition	0 ok	1 fmter	2 srvfa	3 nxdom	4 N/I	5 forbidden
    	QDCOUNT	16 bits: number of questions
	ANCOUNT 16 bits: number of answers
	NSCOUNT 16 bits: authority section (where to ask for actual response - NS RECORDS)
	ARCOUNT 16 bits: additional section (glue records)
QUESTION:
	QNAME	DOMAIN
	QTYPE	16 bits: 1 A 	2 NS	5 CNAME	6 SOA	10 NULL	12 PTR 13 HINFO	15 MX	16 TXT ...
	QCLASS	16 bits: 1 INTERNET	2 CSNET	(obsolete)	3 CHAOS	4 HESIOD	255 ANY ...
ANSWER:
	NAME	DOMAIN
	TYPE	same as QTYPE
	CLASS	same description as QCLASS, except class 255 ANY is not allowed here
	RDLEN	16 bits: length of RDATA field - this is a number 0-65536, no two zero bits
	RDATA	A: 4 bytes IP address		NS: DOMAIN	CNAME: DOMAIN
		SOA: NAME-ns1 NAME-email 32b-serial 32b-refresh 32b-retry 32b-expire 32b-nxdomainttl
		NULL: any data up to RDLEN 	PTR: DOMAIN	HINFO: STRING-CPU, STRING-OS
		MX: 16 bit preference, NAME-like domain		TXT: one or more STRING
*/
/* PCAP file format: GLOBALHEADER PACKETHEADER PACKETDATA PACKETHEADER2 PACKETDATA2 ...
GLOBAL HEADER:	24 bytes
	MAGIC	32 bits: 0xA1B2C3D4 timestamp is s and micros	0xA1B23C4D timestamp is s and nanos
	MAJOR	16 bits: version	2 https://tools.ietf.org/id/draft-gharris-opsawg-pcap-00.html
	MINOR	16 bits: version	4 _/	  /-------------------------------------------------\
	RESERV1	32 bits: unused and set to 0	 < http://en.wikipedia.org/wiki/Frame_check_sequence|
	RESERV2 32 bits: unused and set to 0	  \--------------------------------------------\  ^ |
	SNAPLEN	32 bits: larger or equal to size of largest capture of a single packet		|/ \|
	FCS	 4 bits: if last bit is 1, first 3 tell nr of bytes of FCS appended to every packet/
	LINKTYP	28 bits: pkt type //tcpdump.org/linktypes.html	101 IPv4/v6	1 ether		|   |
PACKET HEADER:	16 bytes
	SECONDS	32 bits: UNIX timestamp
	NANOSEC 32 bits: nanoseconds elapsed since the second, can also be microseconds - see MAGIC
	CAPTURE	32 bits: number of bytes captured from the packet following the header
	ORIGLEN	32 bits: number of bytes of the original packet size (can be more than CAPTURE)
*/
/* IPv4 PACKET: HEADER DATA				https://datatracker.ietf.org/doc/html/rfc791
HEADER:
 /--	VERSION	 4 bits:	4 IPv4	6 IPv6
| T	HEADLEN	 4 bits: >= 5.	Header size 32 bit words (header is padded), so it points to data.
|w	SRVTYPE	 8 bits:	3bPrecedence 1bLowDelay 1bHighThroughput 1bHighReliability 2bReserved
|e		Prec.: 0routine 1prio 2immediate 3flash 4flashoverride 5critic 110inetctrl 111netctrl
|n	LENGTH	16 bits: length including header and data. every host must accept at least 576.
|t	IDENTIF	16 bits: not so unique ID per src-dest persisted across fragmentations for reassembly
|y	FLAGS	 3 bits: bit 0 (1. bit): evil bit, bit 1: don't fragment, bit 2: more fragments
| B	FOFFSET	13 bits: where in complete datagram this fragment belongs in 64 bit words-first has 0
|y	TTL	 8 bits: every router decreases by one, when zero, packet is destroyed
|t	PROTO	 8 bits: datatracker.ietf.org/doc/html/rfc790#page-6	1 ICMP	6 TCP	17 UDP
|e	CHCKSUM	16 bits: 16 bit one's complement of the one's complement sum of 16b words in header
|s	SRCADDR	32 bits:
 \--	DSTADDR 32 bits:
	OPTIONS variable: depending on type, it may be single byte-type or byte-type, byte-len, data.
		Option type byte: 1b-copy to fragmented headers 2b-option class 5b-option number
		Option classes:  0 control	1 reserved	2 debugging	3 reserved
		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 PCAPMAJ 2
#define PCAPMIN 4
#define ETHERNET = 1,
#define IP 101
struct pcap_global {
	uint32_t subsecond		__attribute__((packed));
	uint16_t major			__attribute__((packed));
	uint16_t minor			__attribute__((packed));
	uint32_t reserved[2]		__attribute__((packed));
	uint32_t snaplen		__attribute__((packed));
	uint32_t linktype		__attribute__((packed)); /* FCS in included here for order */
} __attribute__((packed));
struct pcap_packet {
	uint32_t seconds		__attribute__((packed));
	uint32_t subseconds		__attribute__((packed));
	uint32_t capture_length		__attribute__((packed));
	uint32_t original_length	__attribute__((packed));
} __attribute__((packed));
#define LOW_DELAY (1 << 0)
#define HIGH_THROUGHPUT (1 << 1)
#define HIGH_RELIABILITY (1 << 2)
#define ROUTINE (0 << 5)
#define PRIORITY (1 << 5)
#define IMMEDIATE (1 << 6)
#define FLASH (PRIORITY | IMMEDIATE)
#define FLASH_OVERRIDE (1 << 7)
#define CRITICAL (FLASH_OVERRIDE | PRIORITY)
#define INETCTRL (FLASH_OVERRIDE | IMMEDIATE)
#define NETCTRL (FLASH_OVERRIDE | FLASH)
#define HEADLENOR (1 << 6) /* always bitwiseOR the headlen with this to apply the version number */
#define EVIL (1 << 13)
#define DF (1 << 14)
#define MF (1 << 15)
#define ICMP 1
#define TCP 6
#define UDP 17
struct ip {
	uint8_t headlen; /* length of header in 32 bit words (min 5, max 15 = 60B). see HEADLENOR. */
	uint8_t srvtype; /* OR here: LOW_DELAY, HIGH_THROUGHPUT, HIGH_RELIABILITY, ROUTINE, ... */
	uint16_t length			__attribute__((packed)); /* header + data in 8 bit words */
	uint16_t identifier		__attribute__((packed));
	uint8_t foffset; /* fragment offset in 64 bit words. also or here any flags: EVIL, DF, MF */
	uint8_t ttl;			/* ignored for uint8_t */
	uint8_t protocol;		/* ignored for uint8_t */
	uint16_t checksum;		/* ignoref for uint8_t */
	struct in_addr src		__attribute__((packed));
	struct in_addr dst		__attribute__((packed)); /* ----------- 20 bytes */
	char options[];			/* ignored for char[] */
} __attribute__((packed));
enum type {
	A = 1,
	Ns,
	Md,
	Cname = 5, /* we skip the quite obsolete Mf record, luckily Mf (more fragments) is also 4 */
	Soa,
	Mb,
	Mg,
	Mr,
	Null,
	Wks,
	Ptr,
	Hinfo,
	Minfo,
	Mx,
	Txt
};
enum class {
	In = 1,
	Cs,
	Ch,
	He,
	Any = 255
};
#define RESPONSE (1 << 0)								/* :FLAGS */
#define QUESTION (0 << 0)
#define QUERY (1 << 1) /* must be set, even with response, this shows that it's normal query type */
#define IQUERY (1 << 2)
#define STATUS (QUERY | IQUERY)
#define AA (1 << 5)
#define TC (1 << 6)
#define RD (1 << 7)
#define RA (1 << 8)
#define SUCCESS (1 << 12)
#define FORMAT_ERROR (1 << 13)
#define SERVFAIL (SUCCESS | FORMAT_ERROR)
#define NXDOMAIN (1 << 14)
#define NI (NXDOMAIN | SUCCESS)
#define FORBIDDEN (NXDOMAIN | FORMAT_ERROR)
struct header {
	uint16_t xid			__attribute__((packed));
	uint16_t flags			__attribute__((packed));
	uint16_t qdcount		__attribute__((packed));
	uint16_t ancount		__attribute__((packed));
	uint16_t nscount		__attribute__((packed));
	uint16_t arcount		__attribute__((packed));
	char data[];			/* ignored for char[] */
} __attribute__((packed));
int logudp (int o /* fd */, struct sockaddr_in s, struct sockaddr_in d, char * u, size_t l /* d */) {
	if (o == -1)
		return -1;
	struct timespec t;
	if (clock_gettime(CLOCK_REALTIME, &t) == -1) {
		perror("clock_gettime(CLOCK_REALTIME, &t)");
		return -2;
	}
	struct pcap_packet p = {
		.seconds = t.tv_sec,
		.subseconds = t.tv_nsec,
		.capture_length = l,
		.original_length = l
	};
	struct ip i = {
		.headlen = 5 | HEADLENOR,
		.srvtype = ROUTINE,
		.length = htons(8+l),
		.identifier = 0x6969,
		.foffset = 0,
		.ttl = 69,
		.protocol = UDP,
		.checksum = 0, /* wireshark does not validate, at least not on debian 11 */
		.src = s.sin_addr,
		.dst = d.sin_addr
	};
#define LOGUDP_L (sizeof p + sizeof i + 4*2 + l)
	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 v = htons(l);
	c = (char *) memcpy(b, &p, sizeof p) + sizeof p;
	c = (char *) memcpy(c, &i, sizeof i) + sizeof i;
	c = (char *) memcpy(c, &s.sin_port, 2) + 2;
	c = (char *) memcpy(c, &d.sin_port, 2) + 2;
	c = (char *) memcpy(c, &v, 2) + 2;
	c = (char *) memcpy(c, &n, 2) + 2;
	c = (char *) memcpy(c, u, l) + l;
	if (write(o, b, LOGUDP_L) == -1) { /* atomic and thread safe, as per posix */
		perror("write(" STR(LOGUDP_L) ")");
		return -3;
	}
	return LOGUDP_L;
}
int finish = 0;
int c = -1; /* child process */
void handler () {
	if (++finish >= 3) {
		if (c != -1)
			kill(c, SIGHUP);
		exit(1);
	}
}
struct timespec lp = { /* last packet */
	.tv_sec = 0
};
void child_handler () {
	if (clock_gettime(CLOCK_MONOTONIC, &lp) == -1)
		perror("clock_gettime(CLOCK_MONOTONIC, &lp)");
}
int main (int argc, char ** argv) {
	int r = 2;
	struct in_addr a = {
		.s_addr = 0
	};
	struct sockaddr_in b = {
		.sin_family = AF_INET,
		.sin_port = 0,
		.sin_addr = {
			.s_addr = INADDR_ANY
		}
	};
	char * d = "dnsfind.sijanec.eu";
	int s = -1; /* socket */
	int o = -1; /* output file */
	struct in_net * n; /* networks */
	int l; /* count of networks */
	int i = 0; /* network index */
	int j = -1; /* host in network index */
	int t = 1000;
	int w = 1000000;
	struct in_addr h; /* host to scan */
	signal(SIGINT, handler);
	signal(SIGTERM, handler);
	while (1) {
		switch (getopt(argc, argv, ":a:b:d:ho:p:t:w:")) {
			case 'a':
				inet_aton(optarg, &a);
				break;
			case 'b':
				inet_aton(optarg, &b.sin_addr);
				break;
			case 'd':
				d = optarg;
				break;
			case 'h':
				printf(HELP, argv[0]);
				r = 0;
				goto r;
			case 'o':
				if ((o = open(optarg, O_CREAT | O_TRUNC | O_WRONLY, 00664)) == -1) {
					perror("open(optarg, O_CREAT | O_TRUNC | O_WRONLY)");
					r = 3;
					goto r;
				}
				struct pcap_global g = {
					.subsecond = NANOSECOND,
					.major = PCAPMAJ,
					.minor = PCAPMIN,
					.reserved[0] = 0,
					.reserved[1] = 0,
					.snaplen = 65535,
					.linktype = IP
				};
				if (write(o, &g, sizeof g) == -1) {
					perror("write(o, &g, sizeof g)");
					r = 4;
					goto r;
				}
				break;
			case 'p':
				b.sin_port = htons(atoi(optarg));
				break;
			case 't':
				t = atoi(optarg);
				break;
			case 'w':
				w = atoi(optarg);
				break;
			case -1:
				if (!(l = argc-optind)) {
					fprintf(stderr, "specify targets to scan :: " HELP, argv[0]);
					r = 5;
					goto r;
				}
				n = alloca(l*sizeof *n);
				for (int i = optind; i < argc; i++) {
					int w = i-optind;
					n[w] = str2net(argv[i]);
				}
				goto o;
			case '?':
				fprintf(stderr, "unknown option :: " HELP, argv[0]);
				r = 6;
				goto r;
			case ':':
				fprintf(stderr, "missing option argument :: " HELP, argv[0]);
				r = 7;
				goto r;
			default:
				r = 8;
				goto r;
		}
	}
o:
	if (!a.s_addr) {
		int e;
		fprintf(stderr, "resolving %s ... ", d);
		if ((e = resolve(d, &a.s_addr))) {
			fprintf(stderr, "failed: %s\n", gai_strerror(e));
			r = 9;
			goto r;
		}
		fprintf(stderr, " %s\n", inet_ntoa(a));
	}
	if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
		perror("socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)");
		r = 10;
		goto r;
	}
	if (bind(s, (struct sockaddr *) &b, sizeof(struct sockaddr))) {
		perror("bind(s, (struct sokaddr *) &b, sizeof(struct sockaddr))");
		r = 11;
		goto r;
	}
	if ((c = fork()) == -1) {
		perror("fork()");
		r = 12;
		goto r;
	}
	if (!c) {
		signal(SIGINT, child_handler);
		signal(SIGTERM, child_handler);
		while (1) {
			char b[512]; /* max dns packet */
			struct sockaddr_in f;
			socklen_t č = sizeof f;
			if (recvfrom(s,b,512,!lp.tv_sec?MSG_DONTWAIT:0,(struct sockaddr*)&f,&č)==-1){
				if (errno != EWOULDBLOCK) {
					perror("recvfrom(s,b,512,!lp.tv_sec?MSG_DONTWAIT:0,(str...");
					return 1;
				}
				struct timespec z;
				if (clock_gettime(CLOCK_MONOTONIC, &z) == -1) {
					perror("clock_gettime(CLOCK_MONOTONIC, &z)");
					return 2;
				}
				if ((z.tv_sec*1000000 + z.tv_nsec/1000)
						- (lp.tv_sec*1000000 + lp.tv_nsec/1000) > w) {
					fprintf(stderr, "no more packets are received. timeout.\n");
					return 0;
				}
				continue;
			}
			if (lp.tv_sec)
				if (clock_gettime(CLOCK_MONOTONIC, &lp) == -1) {
					perror("clock_gettime(CLOCK_MONOTONIC, &lp)");
					return 2;
				}
			fprintf(stderr, "received response from %s\n", inet_ntoa(f.sin_addr));
		}
		return 0;
	}
	while (!finish) {
		if (!(t = host(n[i], ++j).s_addr)) {
			if (++i >= l) {
				int s;
				fprintf(stderr, "finished sending, waiting for last replies\n");
				kill(c, SIGINT); /* child waits */
				if (wait(&s) == -1) {
					perror("wait(&s)");
					r = 13;
					goto r;
				}
				if (WIFEXITED(s) && !WEXITSTATUS(s)) {
					r = 0;
					goto r;
				}
				r = 14;
				goto r;
			}
			else
				h = host(n[i], (j = 0));
		}
		struct sockaddr_in e = {
			.sin_family = AF_INET,
			.sin_port = htons(53),
			.sin_addr = h
		};
		struct header h = {
			.xid = 0x6969, /* oh no, cache poisoning, whatever'll I do */
			.flags = htons(QUESTION | QUERY | RD),
			.qdcount = htons(1),
			.ancount = 0,
			.nscount = 0,
			.arcount = 0
		};
		int v = domain2name_len(d, strlen(d));
#define L (sizeof h + v + 2*2)
		char * u = alloca(L);
		char * c;
		uint16_t y = htons(A);
		uint16_t k = htons(In);
		c = (char *) memcpy(u, &h, sizeof h) + sizeof h;
		c += domain2name(c, d, strlen(d));
		c = (char *) memcpy(c, &y, 2) + 2;
		c = (char *) memcpy(c, &k, 2) + 2;
		logudp(o, b, e, u, L);
		sendto(s, u, L, 0, (struct sockaddr *) &e, sizeof(struct sockaddr));
		usleep(t);
	}
	if (finish)
		kill(c, SIGTERM); /* stop receiving */
r:
	if (!r && j != -1) {
		char * x = alloca(l*31+strlen("SCANNED  \n0"));
		strcpy(x, "SCANNED ");
		for (int m = 0; m < finish ? i : l; m++) {
			strcat(x, inet_ntoa(n[m].addr));
			strcat(x, "/");
			strcat(x, inet_ntoa(n[m].mask));
			strcat(x, " ");
		}
		strcat(x, "\n");
		write(STDIN_FILENO, x, strlen(x)); /* vsi tele strlen in strcat niso najboljša pot */
	}
	if (s != -1)
		if (close(s))
			perror("close(s)");
	if (o != -1)
		if (close(o))
			perror("close(o)");
	return r;
}