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path: root/src/network/__dns.c
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#include <stdint.h>
#include <netdb.h>
#include <stdio.h>
#include <fcntl.h>
#include <limits.h>
#include <string.h>
#include <sys/socket.h>
#include <poll.h>
#include <netinet/in.h>
#include <time.h>
#include <ctype.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include "__dns.h"
#include "stdio_impl.h"

#define TIMEOUT 5
#define RETRY 1000
#define PACKET_MAX 512
#define PTR_MAX (64 + sizeof ".in-addr.arpa")

static void cleanup(void *p)
{
	close((intptr_t)p);
}

int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
{
	time_t t0 = time(0);
	int fd;
	FILE *f, _f;
	unsigned char _buf[256];
	char line[64], *s, *z;
	union {
		struct sockaddr_in sin;
		struct sockaddr_in6 sin6;
	} sa = {0}, ns[3] = {{0}};
	socklen_t sl = sizeof sa.sin;
	int nns = 0;
	int family = AF_INET;
	unsigned char q[280] = "", *r = dest;
	int ql;
	int rlen;
	int got = 0, failed = 0;
	int errcode = EAI_AGAIN;
	int i, j;
	struct timespec ts;
	struct pollfd pfd;
	int id;
	int cs;

	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

	/* Construct query template - RR and ID will be filled later */
	if (strlen(name)-1 >= 254U) return EAI_NONAME;
	q[2] = q[5] = 1;
	strcpy((char *)q+13, name);
	for (i=13; q[i]; i=j+1) {
		for (j=i; q[j] && q[j] != '.'; j++);
		if (j-i-1u > 62u) return EAI_NONAME;
		q[i-1] = j-i;
	}
	q[i+3] = 1;
	ql = i+4;

	/* Make a reasonably unpredictable id */
	clock_gettime(CLOCK_REALTIME, &ts);
	id = ts.tv_nsec + ts.tv_nsec/65536UL & 0xffff;

	/* Get nameservers from resolv.conf, fallback to localhost */
	f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
	if (f) for (nns=0; nns<3 && fgets(line, sizeof line, f); ) {
		if (strncmp(line, "nameserver", 10) || !isspace(line[10]))
			continue;
		for (s=line+11; isspace(*s); s++);
		for (z=s; *z && !isspace(*z); z++);
		*z=0;
		if (__ipparse(ns+nns, AF_UNSPEC, s) < 0) continue;
		ns[nns].sin.sin_port = htons(53);
		if (ns[nns++].sin.sin_family == AF_INET6) {
			family = AF_INET6;
			sl = sizeof sa.sin6;
		}
	}
	if (f) __fclose_ca(f);
	if (!nns) {
		ns[0].sin.sin_family = family = AF_INET;
		ns[0].sin.sin_port = htons(53);
		ns[0].sin.sin_addr.s_addr = htonl(0x7f000001);
		nns=1;
		sl = sizeof sa.sin;
	}

	/* Get local address and open/bind a socket */
	sa.sin.sin_family = family;
	fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);

	/* Handle case where system lacks IPv6 support */
	if (fd < 0 && errno == EAFNOSUPPORT) {
		if (family != AF_INET6) return EAI_SYSTEM;
		fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
		family = AF_INET;
	}
	if (fd < 0) return EAI_SYSTEM;

	/* Convert any IPv4 addresses in a mixed environment to v4-mapped */
	if (family == AF_INET6) {
		setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
		for (i=0; i<nns; i++) {
			if (ns[i].sin.sin_family != AF_INET) continue;
			memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
				&ns[i].sin.sin_addr, 4);
			memcpy(ns[i].sin6.sin6_addr.s6_addr,
				"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
			ns[i].sin6.sin6_family = AF_INET6;
			ns[i].sin6.sin6_flowinfo = 0;
			ns[i].sin6.sin6_scope_id = 0;
		}
	}

	pthread_cleanup_push(cleanup, (void *)(intptr_t)fd);
	pthread_setcancelstate(cs, 0);

	if (bind(fd, (void *)&sa, sl) < 0) {
		errcode = EAI_SYSTEM;
		goto out;
	}

	pfd.fd = fd;
	pfd.events = POLLIN;

	/* Loop until we timeout; break early on success */
	for (; time(0)-t0 < TIMEOUT; ) {

		/* Query all configured namservers in parallel */
		for (i=0; i<rrcnt; i++) if (rr[i]) for (j=0; j<nns; j++) {
			q[0] = id+i >> 8;
			q[1] = id+i;
			q[ql-3] = rr[i];
			sendto(fd, q, ql, MSG_NOSIGNAL, (void *)&ns[j], sl);
		}

		/* Wait for a response, or until time to retry */
		if (poll(&pfd, 1, RETRY) <= 0) continue;

		/* Process any and all replies */
		while (got+failed < rrcnt && (rlen = recvfrom(fd, r, 512, 0,
			(void *)&sa, (socklen_t[1]){sl})) >= 2)
		{
			/* Ignore replies from addresses we didn't send to */
			for (i=0; i<nns; i++) if (!memcmp(ns+i, &sa, sl)) break;
			if (i==nns) continue;

			/* Compute index of the query from id */
			i = r[0]*256+r[1] - id & 0xffff;
			if ((unsigned)i >= rrcnt || !rr[i]) continue;

			/* Interpret the result code */
			switch (r[3] & 15) {
			case 0:
				got++;
				break;
			case 3:
				if (1) errcode = EAI_NONAME; else
			default:
				errcode = EAI_FAIL;
				failed++;
			}

			/* Mark this record as answered */
			rr[i] = 0;
			r += 512;
		}

		/* Check to see if we have answers to all queries */
		if (got+failed == rrcnt) break;
	}
out:
	pthread_cleanup_pop(1);

	/* Return the number of results, or an error code if none */
	if (got) return got;
	return errcode;
}

static void mkptr4(char *s, const unsigned char *ip)
{
	sprintf(s, "%d.%d.%d.%d.in-addr.arpa",
		ip[3], ip[2], ip[1], ip[0]);
}

static void mkptr6(char *s, const unsigned char *ip)
{
	static const char xdigits[] = "0123456789abcdef";
	int i;
	for (i=15; i>=0; i--) {
		*s++ = xdigits[ip[i]&15]; *s++ = '.';
		*s++ = xdigits[ip[i]>>4]; *s++ = '.';
	}
	strcpy(s, "ip6.arpa");
}

int __dns_query(unsigned char *r, const void *a, int family, int ptr)
{
	char buf[PTR_MAX];
	int rr[2], rrcnt = 1;

	if (ptr) {
		if (family == AF_INET6) mkptr6(buf, a);
		else mkptr4(buf, a);
		rr[0] = RR_PTR;
		a = buf;
	} else if (family == AF_INET6) {
		rr[0] = RR_AAAA;
	} else {
		rr[0] = RR_A;
		if (family != AF_INET) rr[rrcnt++] = RR_AAAA;
	}

	return __dns_doqueries(r, a, rr, rrcnt);
}

int __dn_expand(const unsigned char *, const unsigned char *, const unsigned char *, char *, int);

int __dns_get_rr(void *dest, size_t stride, size_t maxlen, size_t limit, const unsigned char *r, int rr, int dec)
{
	int qdcount, ancount;
	const unsigned char *p;
	char tmp[256];
	int found = 0;
	int len;

	if ((r[3]&15)) return 0;
	p = r+12;
	qdcount = r[4]*256 + r[5];
	ancount = r[6]*256 + r[7];
	if (qdcount+ancount > 64) return -1;
	while (qdcount--) {
		while (p-r < 512 && *p-1U < 127) p++;
		if (*p>193 || (*p==193 && p[1]>254) || p>r+506)
			return -1;
		p += 5 + !!*p;
	}
	while (ancount--) {
		while (p-r < 512 && *p-1U < 127) p++;
		if (*p>193 || (*p==193 && p[1]>254) || p>r+506)
			return -1;
		p += 1 + !!*p;
		len = p[8]*256 + p[9];
		if (p+len > r+512) return -1;
		if (p[1]==rr && len <= maxlen) {
			if (dec && __dn_expand(r, r+512, p+10, tmp, sizeof tmp)<0)
				return -1;
			if (dest && limit) {
				if (dec) strcpy(dest, tmp);
				else memcpy(dest, p+10, len);
				dest = (char *)dest + stride;
				limit--;
			}
			found++;
		}
		p += 10 + len;
	}
	return found;
}

int __dns_count_addrs(const unsigned char *r, int cnt)
{
	int found=0, res, i;
	static const int p[2][2] = { { 4, RR_A }, { 16, RR_AAAA } };

	while (cnt--) {
		for (i=0; i<2; i++) {
			res = __dns_get_rr(0, 0, p[i][0], -1, r, p[i][1], 0);
			if (res < 0) return res;
			found += res;
		}
		r += 512;
	}
	return found;
}