Rich Felker
7603c5f127
a v6 socket will only be used if there is at least one v6 nameserver address. if the kernel lacks v6 support, the code will fall back to using a v4 socket and requests to v6 servers will silently fail. when using a v6 socket, v4 addresses are converted to v4-mapped form and setsockopt is used to ensure that the v6 socket can accept both v4 and v6 traffic (this is on-by-default on Linux but the default is configurable in /proc and so it needs to be set explicitly on the socket level). this scheme avoids increasing resource usage during lookups and allows the existing network io loop to be used without modification. previously, nameservers whose address family did not match the address family of the first-listed nameserver were simply ignored. prior to recent __ipparse fixes, they were not ignored but erroneously parsed.
283 lines
6.7 KiB
C
283 lines
6.7 KiB
C
#include <stdint.h>
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#include <netdb.h>
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#include <stdio.h>
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#include <fcntl.h>
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#include <limits.h>
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#include <string.h>
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#include <sys/socket.h>
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#include <poll.h>
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#include <netinet/in.h>
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#include <time.h>
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#include <ctype.h>
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#include <unistd.h>
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#include <pthread.h>
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#include <errno.h>
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#include "__dns.h"
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#include "stdio_impl.h"
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#define TIMEOUT 5
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#define RETRY 1000
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#define PACKET_MAX 512
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#define PTR_MAX (64 + sizeof ".in-addr.arpa")
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static void cleanup(void *p)
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{
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close((intptr_t)p);
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}
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int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
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{
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time_t t0 = time(0);
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int fd;
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FILE *f, _f;
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unsigned char _buf[256];
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char line[64], *s, *z;
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union {
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struct sockaddr_in sin;
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struct sockaddr_in6 sin6;
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} sa = {0}, ns[3] = {{0}};
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socklen_t sl = sizeof sa.sin;
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int nns = 0;
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int family = AF_INET;
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unsigned char q[280] = "", *r = dest;
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int ql;
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int rlen;
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int got = 0, failed = 0;
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int errcode = EAI_AGAIN;
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int i, j;
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struct timespec ts;
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struct pollfd pfd;
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int id;
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int cs;
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pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
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/* Construct query template - RR and ID will be filled later */
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if (strlen(name)-1 >= 254U) return EAI_NONAME;
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q[2] = q[5] = 1;
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strcpy((char *)q+13, name);
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for (i=13; q[i]; i=j+1) {
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for (j=i; q[j] && q[j] != '.'; j++);
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if (j-i-1u > 62u) return EAI_NONAME;
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q[i-1] = j-i;
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}
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q[i+3] = 1;
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ql = i+4;
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/* Make a reasonably unpredictable id */
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clock_gettime(CLOCK_REALTIME, &ts);
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id = ts.tv_nsec + ts.tv_nsec/65536UL & 0xffff;
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/* Get nameservers from resolv.conf, fallback to localhost */
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f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
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if (f) for (nns=0; nns<3 && fgets(line, sizeof line, f); ) {
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if (strncmp(line, "nameserver", 10) || !isspace(line[10]))
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continue;
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for (s=line+11; isspace(*s); s++);
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for (z=s; *z && !isspace(*z); z++);
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*z=0;
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if (__ipparse(ns+nns, AF_UNSPEC, s) < 0) continue;
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ns[nns].sin.sin_port = htons(53);
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if (ns[nns++].sin.sin_family == AF_INET6) {
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family = AF_INET6;
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sl = sizeof sa.sin6;
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}
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}
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if (f) __fclose_ca(f);
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if (!nns) {
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ns[0].sin.sin_family = family = AF_INET;
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ns[0].sin.sin_port = htons(53);
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ns[0].sin.sin_addr.s_addr = htonl(0x7f000001);
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nns=1;
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sl = sizeof sa.sin;
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}
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/* Get local address and open/bind a socket */
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sa.sin.sin_family = family;
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fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
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/* Handle case where system lacks IPv6 support */
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if (fd < 0 && errno == EAFNOSUPPORT) {
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if (family != AF_INET6) return EAI_SYSTEM;
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fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
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family = AF_INET;
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}
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if (fd < 0) return EAI_SYSTEM;
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/* Convert any IPv4 addresses in a mixed environment to v4-mapped */
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if (family == AF_INET6) {
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setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
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for (i=0; i<nns; i++) {
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if (ns[i].sin.sin_family != AF_INET) continue;
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memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
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&ns[i].sin.sin_addr, 4);
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memcpy(ns[i].sin6.sin6_addr.s6_addr,
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"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
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ns[i].sin6.sin6_family = AF_INET6;
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ns[i].sin6.sin6_flowinfo = 0;
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ns[i].sin6.sin6_scope_id = 0;
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}
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}
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pthread_cleanup_push(cleanup, (void *)(intptr_t)fd);
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pthread_setcancelstate(cs, 0);
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if (bind(fd, (void *)&sa, sl) < 0) {
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errcode = EAI_SYSTEM;
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goto out;
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}
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pfd.fd = fd;
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pfd.events = POLLIN;
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/* Loop until we timeout; break early on success */
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for (; time(0)-t0 < TIMEOUT; ) {
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/* Query all configured namservers in parallel */
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for (i=0; i<rrcnt; i++) if (rr[i]) for (j=0; j<nns; j++) {
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q[0] = id+i >> 8;
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q[1] = id+i;
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q[ql-3] = rr[i];
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sendto(fd, q, ql, MSG_NOSIGNAL, (void *)&ns[j], sl);
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}
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/* Wait for a response, or until time to retry */
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if (poll(&pfd, 1, RETRY) <= 0) continue;
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/* Process any and all replies */
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while (got+failed < rrcnt && (rlen = recvfrom(fd, r, 512, 0,
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(void *)&sa, (socklen_t[1]){sl})) >= 2)
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{
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/* Ignore replies from addresses we didn't send to */
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for (i=0; i<nns; i++) if (!memcmp(ns+i, &sa, sl)) break;
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if (i==nns) continue;
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/* Compute index of the query from id */
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i = r[0]*256+r[1] - id & 0xffff;
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if ((unsigned)i >= rrcnt || !rr[i]) continue;
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/* Interpret the result code */
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switch (r[3] & 15) {
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case 0:
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got++;
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break;
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case 3:
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if (1) errcode = EAI_NONAME; else
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default:
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errcode = EAI_FAIL;
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failed++;
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}
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/* Mark this record as answered */
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rr[i] = 0;
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r += 512;
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}
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/* Check to see if we have answers to all queries */
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if (got+failed == rrcnt) break;
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}
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out:
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pthread_cleanup_pop(1);
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/* Return the number of results, or an error code if none */
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if (got) return got;
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return errcode;
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}
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static void mkptr4(char *s, const unsigned char *ip)
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{
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sprintf(s, "%d.%d.%d.%d.in-addr.arpa",
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ip[3], ip[2], ip[1], ip[0]);
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}
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static void mkptr6(char *s, const unsigned char *ip)
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{
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static const char xdigits[] = "0123456789abcdef";
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int i;
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for (i=15; i>=0; i--) {
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*s++ = xdigits[ip[i]&15]; *s++ = '.';
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*s++ = xdigits[ip[i]>>4]; *s++ = '.';
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}
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strcpy(s, "ip6.arpa");
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}
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int __dns_query(unsigned char *r, const void *a, int family, int ptr)
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{
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char buf[PTR_MAX];
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int rr[2], rrcnt = 1;
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if (ptr) {
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if (family == AF_INET6) mkptr6(buf, a);
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else mkptr4(buf, a);
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rr[0] = RR_PTR;
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a = buf;
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} else if (family == AF_INET6) {
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rr[0] = RR_AAAA;
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} else {
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rr[0] = RR_A;
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if (family != AF_INET) rr[rrcnt++] = RR_AAAA;
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}
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return __dns_doqueries(r, a, rr, rrcnt);
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}
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int __dn_expand(const unsigned char *, const unsigned char *, const unsigned char *, char *, int);
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int __dns_get_rr(void *dest, size_t stride, size_t maxlen, size_t limit, const unsigned char *r, int rr, int dec)
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{
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int qdcount, ancount;
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const unsigned char *p;
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char tmp[256];
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int found = 0;
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int len;
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if ((r[3]&15)) return 0;
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p = r+12;
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qdcount = r[4]*256 + r[5];
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ancount = r[6]*256 + r[7];
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if (qdcount+ancount > 64) return -1;
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while (qdcount--) {
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while (p-r < 512 && *p-1U < 127) p++;
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if (*p>193 || (*p==193 && p[1]>254) || p>r+506)
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return -1;
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p += 5 + !!*p;
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}
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while (ancount--) {
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while (p-r < 512 && *p-1U < 127) p++;
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if (*p>193 || (*p==193 && p[1]>254) || p>r+506)
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return -1;
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p += 1 + !!*p;
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len = p[8]*256 + p[9];
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if (p+len > r+512) return -1;
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if (p[1]==rr && len <= maxlen) {
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if (dec && __dn_expand(r, r+512, p+10, tmp, sizeof tmp)<0)
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return -1;
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if (dest && limit) {
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if (dec) strcpy(dest, tmp);
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else memcpy(dest, p+10, len);
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dest = (char *)dest + stride;
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limit--;
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}
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found++;
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}
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p += 10 + len;
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}
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return found;
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}
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int __dns_count_addrs(const unsigned char *r, int cnt)
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{
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int found=0, res, i;
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static const int p[2][2] = { { 4, RR_A }, { 16, RR_AAAA } };
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while (cnt--) {
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for (i=0; i<2; i++) {
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res = __dns_get_rr(0, 0, p[i][0], -1, r, p[i][1], 0);
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if (res < 0) return res;
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found += res;
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}
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r += 512;
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}
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return found;
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}
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