src/network/res_msend.c

   1 #include <sys/socket.h>
   2 #include <netinet/in.h>
   3 #include <netinet/tcp.h>
   4 #include <netdb.h>
   5 #include <arpa/inet.h>
   6 #include <stdint.h>
   7 #include <string.h>
   8 #include <poll.h>
   9 #include <time.h>
  10 #include <ctype.h>
  11 #include <unistd.h>
  12 #include <errno.h>
  13 #include <pthread.h>
  14 #include "stdio_impl.h"
  15 #include "syscall.h"
  16 #include "lookup.h"
  17
  18 static void cleanup(void *p)
  19 {
  20         struct pollfd *pfd = p;
  21         for (int i=0; pfd[i].fd >= -1; i++)
  22                 if (pfd[i].fd >= 0) __syscall(SYS_close, pfd[i].fd);
  23 }
  24
  25 static unsigned long mtime()
  26 {
  27         struct timespec ts;
  28         clock_gettime(CLOCK_REALTIME, &ts);
  29         return (unsigned long)ts.tv_sec * 1000
  30                 + ts.tv_nsec / 1000000;
  31 }
  32
  33 static int start_tcp(struct pollfd *pfd, int family, const void *sa, socklen_t sl, const unsigned char *q, int ql)
  34 {
  35         struct msghdr mh = {
  36                 .msg_name = (void *)sa,
  37                 .msg_namelen = sl,
  38                 .msg_iovlen = 2,
  39                 .msg_iov = (struct iovec [2]){
  40                         { .iov_base = (uint8_t[]){ ql>>8, ql }, .iov_len = 2 },
  41                         { .iov_base = (void *)q, .iov_len = ql } }
  42         };
  43         int r;
  44         int fd = socket(family, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
  45         pfd->fd = fd;
  46         pfd->events = POLLOUT;
  47         if (!setsockopt(fd, IPPROTO_TCP, TCP_FASTOPEN_CONNECT,
  48             &(int){1}, sizeof(int))) {
  49                 r = sendmsg(fd, &mh, MSG_FASTOPEN|MSG_NOSIGNAL);
  50                 if (r == ql+2) pfd->events = POLLIN;
  51                 if (r >= 0) return r;
  52                 if (errno == EINPROGRESS) return 0;
  53         }
  54         r = connect(fd, sa, sl);
  55         if (!r || errno == EINPROGRESS) return 0;
  56         close(fd);
  57         pfd->fd = -1;
  58         return -1;
  59 }
  60
  61 static void step_mh(struct msghdr *mh, size_t n)
  62 {
  63         /* Adjust iovec in msghdr to skip first n bytes. */
  64         while (mh->msg_iovlen && n >= mh->msg_iov->iov_len) {
  65                 n -= mh->msg_iov->iov_len;
  66                 mh->msg_iov++;
  67                 mh->msg_iovlen--;
  68         }
  69         if (!mh->msg_iovlen) return;
  70         mh->msg_iov->iov_base = (char *)mh->msg_iov->iov_base + n;
  71         mh->msg_iov->iov_len -= n;
  72 }
  73
  74 /* Internal contract for __res_msend[_rc]: asize must be >=512, nqueries
  75  * must be sufficiently small to be safe as VLA size. In practice it's
  76  * either 1 or 2, anyway. */
  77
  78 int __res_msend_rc(int nqueries, const unsigned char *const *queries,
  79         const int *qlens, unsigned char *const *answers, int *alens, int asize,
  80         const struct resolvconf *conf)
  81 {
  82         int fd;
  83         int timeout, attempts, retry_interval, servfail_retry;
  84         union {
  85                 struct sockaddr_in sin;
  86                 struct sockaddr_in6 sin6;
  87         } sa = {0}, ns[MAXNS] = {{0}};
  88         socklen_t sl = sizeof sa.sin;
  89         int nns = 0;
  90         int family = AF_INET;
  91         int rlen;
  92         int next;
  93         int i, j;
  94         int cs;
  95         struct pollfd pfd[nqueries+2];
  96         int qpos[nqueries], apos[nqueries];
  97         unsigned char alen_buf[nqueries][2];
  98         int r;
  99         unsigned long t0, t1, t2;
 100
 101         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 102
 103         timeout = 1000*conf->timeout;
 104         attempts = conf->attempts;
 105
 106         for (nns=0; nns<conf->nns; nns++) {
 107                 const struct address *iplit = &conf->ns[nns];
 108                 if (iplit->family == AF_INET) {
 109                         memcpy(&ns[nns].sin.sin_addr, iplit->addr, 4);
 110                         ns[nns].sin.sin_port = htons(53);
 111                         ns[nns].sin.sin_family = AF_INET;
 112                 } else {
 113                         sl = sizeof sa.sin6;
 114                         memcpy(&ns[nns].sin6.sin6_addr, iplit->addr, 16);
 115                         ns[nns].sin6.sin6_port = htons(53);
 116                         ns[nns].sin6.sin6_scope_id = iplit->scopeid;
 117                         ns[nns].sin6.sin6_family = family = AF_INET6;
 118                 }
 119         }
 120
 121         /* Get local address and open/bind a socket */
 122         fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 123
 124         /* Handle case where system lacks IPv6 support */
 125         if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
 126                 for (i=0; i<nns && conf->ns[nns].family == AF_INET6; i++);
 127                 if (i==nns) {
 128                         pthread_setcancelstate(cs, 0);
 129                         return -1;
 130                 }
 131                 fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 132                 family = AF_INET;
 133                 sl = sizeof sa.sin;
 134         }
 135         sa.sin.sin_family = family;
 136         if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) {
 137                 if (fd >= 0) close(fd);
 138                 pthread_setcancelstate(cs, 0);
 139                 return -1;
 140         }
 141
 142         /* Past this point, there are no errors. Each individual query will
 143          * yield either no reply (indicated by zero length) or an answer
 144          * packet which is up to the caller to interpret. */
 145
 146         for (i=0; i<nqueries; i++) pfd[i].fd = -1;
 147         pfd[nqueries].fd = fd;
 148         pfd[nqueries].events = POLLIN;
 149         pfd[nqueries+1].fd = -2;
 150
 151         pthread_cleanup_push(cleanup, pfd);
 152         pthread_setcancelstate(cs, 0);
 153
 154         /* Convert any IPv4 addresses in a mixed environment to v4-mapped */
 155         if (family == AF_INET6) {
 156                 setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
 157                 for (i=0; i<nns; i++) {
 158                         if (ns[i].sin.sin_family != AF_INET) continue;
 159                         memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
 160                                 &ns[i].sin.sin_addr, 4);
 161                         memcpy(ns[i].sin6.sin6_addr.s6_addr,
 162                                 "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 163                         ns[i].sin6.sin6_family = AF_INET6;
 164                         ns[i].sin6.sin6_flowinfo = 0;
 165                         ns[i].sin6.sin6_scope_id = 0;
 166                 }
 167         }
 168
 169         memset(alens, 0, sizeof *alens * nqueries);
 170
 171         retry_interval = timeout / attempts;
 172         next = 0;
 173         t0 = t2 = mtime();
 174         t1 = t2 - retry_interval;
 175
 176         for (; t2-t0 < timeout; t2=mtime()) {
 177                 /* This is the loop exit condition: that all queries
 178                  * have an accepted answer. */
 179                 for (i=0; i<nqueries && alens[i]>0; i++);
 180                 if (i==nqueries) break;
 181
 182                 if (t2-t1 >= retry_interval) {
 183                         /* Query all configured namservers in parallel */
 184                         for (i=0; i<nqueries; i++)
 185                                 if (!alens[i])
 186                                         for (j=0; j<nns; j++)
 187                                                 sendto(fd, queries[i],
 188                                                         qlens[i], MSG_NOSIGNAL,
 189                                                         (void *)&ns[j], sl);
 190                         t1 = t2;
 191                         servfail_retry = 2 * nqueries;
 192                 }
 193
 194                 /* Wait for a response, or until time to retry */
 195                 if (poll(pfd, nqueries+1, t1+retry_interval-t2) <= 0) continue;
 196
 197                 while (next < nqueries) {
 198                         struct msghdr mh = {
 199                                 .msg_name = (void *)&sa,
 200                                 .msg_namelen = sl,
 201                                 .msg_iovlen = 1,
 202                                 .msg_iov = (struct iovec []){
 203                                         { .iov_base = (void *)answers[next],
 204                                           .iov_len = asize }
 205                                 }
 206                         };
 207                         rlen = recvmsg(fd, &mh, 0);
 208                         if (rlen < 0) break;
 209
 210                         /* Ignore non-identifiable packets */
 211                         if (rlen < 4) continue;
 212
 213                         /* Ignore replies from addresses we didn't send to */
 214                         for (j=0; j<nns && memcmp(ns+j, &sa, sl); j++);
 215                         if (j==nns) continue;
 216
 217                         /* Find which query this answer goes with, if any */
 218                         for (i=next; i<nqueries && (
 219                                 answers[next][0] != queries[i][0] ||
 220                                 answers[next][1] != queries[i][1] ); i++);
 221                         if (i==nqueries) continue;
 222                         if (alens[i]) continue;
 223
 224                         /* Only accept positive or negative responses;
 225                          * retry immediately on server failure, and ignore
 226                          * all other codes such as refusal. */
 227                         switch (answers[next][3] & 15) {
 228                         case 0:
 229                         case 3:
 230                                 break;
 231                         case 2:
 232                                 if (servfail_retry && servfail_retry--)
 233                                         sendto(fd, queries[i],
 234                                                 qlens[i], MSG_NOSIGNAL,
 235                                                 (void *)&ns[j], sl);
 236                         default:
 237                                 continue;
 238                         }
 239
 240                         /* Store answer in the right slot, or update next
 241                          * available temp slot if it's already in place. */
 242                         alens[i] = rlen;
 243                         if (i == next)
 244                                 for (; next<nqueries && alens[next]; next++);
 245                         else
 246                                 memcpy(answers[i], answers[next], rlen);
 247
 248                         /* Ignore further UDP if all slots full or TCP-mode */
 249                         if (next == nqueries) pfd[nqueries].events = 0;
 250
 251                         /* If answer is truncated (TC bit), fallback to TCP */
 252                         if ((answers[i][2] & 2) || (mh.msg_flags & MSG_TRUNC)) {
 253                                 alens[i] = -1;
 254                                 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
 255                                 r = start_tcp(pfd+i, family, ns+j, sl, queries[i], qlens[i]);
 256                                 pthread_setcancelstate(cs, 0);
 257                                 if (r >= 0) {
 258                                         qpos[i] = r;
 259                                         apos[i] = 0;
 260                                 }
 261                                 continue;
 262                         }
 263                 }
 264
 265                 for (i=0; i<nqueries; i++) if (pfd[i].revents & POLLOUT) {
 266                         struct msghdr mh = {
 267                                 .msg_iovlen = 2,
 268                                 .msg_iov = (struct iovec [2]){
 269                                         { .iov_base = (uint8_t[]){ qlens[i]>>8, qlens[i] }, .iov_len = 2 },
 270                                         { .iov_base = (void *)queries[i], .iov_len = qlens[i] } }
 271                         };
 272                         step_mh(&mh, qpos[i]);
 273                         r = sendmsg(pfd[i].fd, &mh, MSG_NOSIGNAL);
 274                         if (r < 0) goto out;
 275                         qpos[i] += r;
 276                         if (qpos[i] == qlens[i]+2)
 277                                 pfd[i].events = POLLIN;
 278                 }
 279
 280                 for (i=0; i<nqueries; i++) if (pfd[i].revents & POLLIN) {
 281                         struct msghdr mh = {
 282                                 .msg_iovlen = 2,
 283                                 .msg_iov = (struct iovec [2]){
 284                                         { .iov_base = alen_buf[i], .iov_len = 2 },
 285                                         { .iov_base = answers[i], .iov_len = asize } }
 286                         };
 287                         step_mh(&mh, apos[i]);
 288                         r = recvmsg(pfd[i].fd, &mh, 0);
 289                         if (r < 0) goto out;
 290                         apos[i] += r;
 291                         if (apos[i] < 2) continue;
 292                         int alen = alen_buf[i][0]*256 + alen_buf[i][1];
 293                         if (alen < 13) goto out;
 294                         if (apos[i] < alen+2 && apos[i] < asize+2)
 295                                 continue;
 296                         int rcode = answers[i][3] & 15;
 297                         if (rcode != 0 && rcode != 3)
 298                                 goto out;
 299
 300                         /* Storing the length here commits the accepted answer.
 301                          * Immediately close TCP socket so as not to consume
 302                          * resources we no longer need. */
 303                         alens[i] = alen;
 304                         __syscall(SYS_close, pfd[i].fd);
 305                         pfd[i].fd = -1;
 306                 }
 307         }
 308 out:
 309         pthread_cleanup_pop(1);
 310
 311         /* Disregard any incomplete TCP results */
 312         for (i=0; i<nqueries; i++) if (alens[i]<0) alens[i] = 0;
 313
 314         return 0;
 315 }
 316
 317 int __res_msend(int nqueries, const unsigned char *const *queries,
 318         const int *qlens, unsigned char *const *answers, int *alens, int asize)
 319 {
 320         struct resolvconf conf;
 321         if (__get_resolv_conf(&conf, 0, 0) < 0) return -1;
 322         return __res_msend_rc(nqueries, queries, qlens, answers, alens, asize, &conf);
 323 }