nsz Git - musl/blob - src/network/res_msend.c

   1 #include <sys/socket.h>
   2 #include <netinet/in.h>
   3 #include <netdb.h>
   4 #include <arpa/inet.h>
   5 #include <stdint.h>
   6 #include <string.h>
   7 #include <poll.h>
   8 #include <time.h>
   9 #include <ctype.h>
  10 #include <unistd.h>
  11 #include <errno.h>
  12 #include <pthread.h>
  13 #include "stdio_impl.h"
  14 #include "syscall.h"
  15 #include "lookup.h"
  16
  17 static void cleanup(void *p)
  18 {
  19         __syscall(SYS_close, (intptr_t)p);
  20 }
  21
  22 static unsigned long mtime()
  23 {
  24         struct timespec ts;
  25         clock_gettime(CLOCK_REALTIME, &ts);
  26         return (unsigned long)ts.tv_sec * 1000
  27                 + ts.tv_nsec / 1000000;
  28 }
  29
  30 int __res_msend(int nqueries, const unsigned char *const *queries,
  31         const int *qlens, unsigned char *const *answers, int *alens, int asize)
  32 {
  33         int fd;
  34         FILE *f, _f;
  35         unsigned char _buf[256];
  36         char line[64], *s, *z;
  37         int timeout = 5000, attempts = 2, retry_interval, servfail_retry;
  38         union {
  39                 struct sockaddr_in sin;
  40                 struct sockaddr_in6 sin6;
  41         } sa = {0}, ns[3] = {{0}};
  42         socklen_t sl = sizeof sa.sin;
  43         int nns = 0;
  44         int family = AF_INET;
  45         int rlen;
  46         int next;
  47         int i, j;
  48         int cs;
  49         struct pollfd pfd;
  50         unsigned long t0, t1, t2;
  51         struct address iplit;
  52
  53         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
  54
  55         /* Get nameservers from resolv.conf, fallback to localhost */
  56         f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
  57         if (!f) switch (errno) {
  58         case ENOENT:
  59         case ENOTDIR:
  60         case EACCES:
  61                 goto no_resolv_conf;
  62         default:
  63                 return -1;
  64         }
  65         for (nns=0; nns<3 && fgets(line, sizeof line, f); ) {
  66                 if (!strncmp(line, "options", 7) && isspace(line[7])) {
  67                         unsigned long x;
  68                         char *p, *z;
  69                         p = strstr(line, "timeout:");
  70                         if (p && isdigit(p[8])) {
  71                                 p += 8;
  72                                 x = strtoul(p, &z, 10);
  73                                 if (z != p) timeout = x < 30 ? x*1000 : 30000;
  74                         }
  75                         p = strstr(line, "attempts:");
  76                         if (p && isdigit(p[9])) {
  77                                 p += 9;
  78                                 x = strtoul(p, &z, 10);
  79                                 if (z != p) attempts = x < 10 ? x : 10;
  80                                 if (!attempts) attempts = 1;
  81                         }
  82                 }
  83                 if (strncmp(line, "nameserver", 10) || !isspace(line[10]))
  84                         continue;
  85                 for (s=line+11; isspace(*s); s++);
  86                 for (z=s; *z && !isspace(*z); z++);
  87                 *z=0;
  88
  89                 if (__lookup_ipliteral(&iplit, s, AF_UNSPEC)>0) {
  90                         if (iplit.family == AF_INET) {
  91                                 memcpy(&ns[nns].sin.sin_addr, iplit.addr, 4);
  92                                 ns[nns].sin.sin_port = htons(53);
  93                                 ns[nns++].sin.sin_family = AF_INET;
  94                         } else {
  95                                 sl = sizeof sa.sin6;
  96                                 memcpy(&ns[nns].sin6.sin6_addr, iplit.addr, 16);
  97                                 ns[nns].sin6.sin6_port = htons(53);
  98                                 ns[nns].sin6.sin6_scope_id = iplit.scopeid;
  99                                 ns[nns++].sin6.sin6_family = family = AF_INET6;
 100                         }
 101                 }
 102         }
 103         __fclose_ca(f);
 104 no_resolv_conf:
 105         if (!nns) {
 106                 ns[0].sin.sin_family = AF_INET;
 107                 ns[0].sin.sin_port = htons(53);
 108                 ns[0].sin.sin_addr.s_addr = htonl(0x7f000001);
 109                 nns=1;
 110         }
 111
 112         /* Get local address and open/bind a socket */
 113         sa.sin.sin_family = family;
 114         fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 115
 116         /* Handle case where system lacks IPv6 support */
 117         if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
 118                 fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 119                 family = AF_INET;
 120         }
 121         if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) return -1;
 122
 123         /* Past this point, there are no errors. Each individual query will
 124          * yield either no reply (indicated by zero length) or an answer
 125          * packet which is up to the caller to interpret. */
 126
 127         pthread_cleanup_push(cleanup, (void *)(intptr_t)fd);
 128         pthread_setcancelstate(cs, 0);
 129
 130         /* Convert any IPv4 addresses in a mixed environment to v4-mapped */
 131         if (family == AF_INET6) {
 132                 setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
 133                 for (i=0; i<nns; i++) {
 134                         if (ns[i].sin.sin_family != AF_INET) continue;
 135                         memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
 136                                 &ns[i].sin.sin_addr, 4);
 137                         memcpy(ns[i].sin6.sin6_addr.s6_addr,
 138                                 "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 139                         ns[i].sin6.sin6_family = AF_INET6;
 140                         ns[i].sin6.sin6_flowinfo = 0;
 141                         ns[i].sin6.sin6_scope_id = 0;
 142                 }
 143         }
 144
 145         memset(alens, 0, sizeof *alens * nqueries);
 146
 147         pfd.fd = fd;
 148         pfd.events = POLLIN;
 149         retry_interval = timeout / attempts;
 150         next = 0;
 151         t0 = t2 = mtime();
 152         t1 = t2 - retry_interval;
 153
 154         for (; t2-t0 < timeout; t2=mtime()) {
 155                 if (t2-t1 >= retry_interval) {
 156                         /* Query all configured namservers in parallel */
 157                         for (i=0; i<nqueries; i++)
 158                                 if (!alens[i])
 159                                         for (j=0; j<nns; j++)
 160                                                 sendto(fd, queries[i],
 161                                                         qlens[i], MSG_NOSIGNAL,
 162                                                         (void *)&ns[j], sl);
 163                         t1 = t2;
 164                         servfail_retry = 2 * nqueries;
 165                 }
 166
 167                 /* Wait for a response, or until time to retry */
 168                 if (poll(&pfd, 1, t1+retry_interval-t2) <= 0) continue;
 169
 170                 while ((rlen = recvfrom(fd, answers[next], asize, 0,
 171                   (void *)&sa, (socklen_t[1]){sl})) >= 0) {
 172
 173                         /* Ignore non-identifiable packets */
 174                         if (rlen < 4) continue;
 175
 176                         /* Ignore replies from addresses we didn't send to */
 177                         for (j=0; j<nns && memcmp(ns+j, &sa, sl); j++);
 178                         if (j==nns) continue;
 179
 180                         /* Find which query this answer goes with, if any */
 181                         for (i=next; i<nqueries && (
 182                                 answers[next][0] != queries[i][0] ||
 183                                 answers[next][1] != queries[i][1] ); i++);
 184                         if (i==nqueries) continue;
 185                         if (alens[i]) continue;
 186
 187                         /* Only accept positive or negative responses;
 188                          * retry immediately on server failure, and ignore
 189                          * all other codes such as refusal. */
 190                         switch (answers[next][3] & 15) {
 191                         case 0:
 192                         case 3:
 193                                 break;
 194                         case 2:
 195                                 if (servfail_retry && servfail_retry--)
 196                                         sendto(fd, queries[i],
 197                                                 qlens[i], MSG_NOSIGNAL,
 198                                                 (void *)&ns[j], sl);
 199                         default:
 200                                 continue;
 201                         }
 202
 203                         /* Store answer in the right slot, or update next
 204                          * available temp slot if it's already in place. */
 205                         alens[i] = rlen;
 206                         if (i == next)
 207                                 for (; next<nqueries && alens[next]; next++);
 208                         else
 209                                 memcpy(answers[i], answers[next], rlen);
 210
 211                         if (next == nqueries) goto out;
 212                 }
 213         }
 214 out:
 215         pthread_cleanup_pop(1);
 216
 217         return 0;
 218 }