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         if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0 && errno == ENOSYS)
  29                 clock_gettime(CLOCK_REALTIME, &ts);
  30         return (unsigned long)ts.tv_sec * 1000
  31                 + ts.tv_nsec / 1000000;
  32 }
  33
  34 static int start_tcp(struct pollfd *pfd, int family, const void *sa, socklen_t sl, const unsigned char *q, int ql)
  35 {
  36         struct msghdr mh = {
  37                 .msg_name = (void *)sa,
  38                 .msg_namelen = sl,
  39                 .msg_iovlen = 2,
  40                 .msg_iov = (struct iovec [2]){
  41                         { .iov_base = (uint8_t[]){ ql>>8, ql }, .iov_len = 2 },
  42                         { .iov_base = (void *)q, .iov_len = ql } }
  43         };
  44         int r;
  45         int fd = socket(family, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
  46         pfd->fd = fd;
  47         pfd->events = POLLOUT;
  48         if (!setsockopt(fd, IPPROTO_TCP, TCP_FASTOPEN_CONNECT,
  49             &(int){1}, sizeof(int))) {
  50                 r = sendmsg(fd, &mh, MSG_FASTOPEN|MSG_NOSIGNAL);
  51                 if (r == ql+2) pfd->events = POLLIN;
  52                 if (r >= 0) return r;
  53                 if (errno == EINPROGRESS) return 0;
  54         }
  55         r = connect(fd, sa, sl);
  56         if (!r || errno == EINPROGRESS) return 0;
  57         close(fd);
  58         pfd->fd = -1;
  59         return -1;
  60 }
  61
  62 static void step_mh(struct msghdr *mh, size_t n)
  63 {
  64         /* Adjust iovec in msghdr to skip first n bytes. */
  65         while (mh->msg_iovlen && n >= mh->msg_iov->iov_len) {
  66                 n -= mh->msg_iov->iov_len;
  67                 mh->msg_iov++;
  68                 mh->msg_iovlen--;
  69         }
  70         if (!mh->msg_iovlen) return;
  71         mh->msg_iov->iov_base = (char *)mh->msg_iov->iov_base + n;
  72         mh->msg_iov->iov_len -= n;
  73 }
  74
  75 /* Internal contract for __res_msend[_rc]: asize must be >=512, nqueries
  76  * must be sufficiently small to be safe as VLA size. In practice it's
  77  * either 1 or 2, anyway. */
  78
  79 int __res_msend_rc(int nqueries, const unsigned char *const *queries,
  80         const int *qlens, unsigned char *const *answers, int *alens, int asize,
  81         const struct resolvconf *conf)
  82 {
  83         int fd;
  84         int timeout, attempts, retry_interval, servfail_retry;
  85         union {
  86                 struct sockaddr_in sin;
  87                 struct sockaddr_in6 sin6;
  88         } sa = {0}, ns[MAXNS] = {{0}};
  89         socklen_t sl = sizeof sa.sin;
  90         int nns = 0;
  91         int family = AF_INET;
  92         int rlen;
  93         int next;
  94         int i, j;
  95         int cs;
  96         struct pollfd pfd[nqueries+2];
  97         int qpos[nqueries], apos[nqueries];
  98         unsigned char alen_buf[nqueries][2];
  99         int r;
 100         unsigned long t0, t1, t2;
 101
 102         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 103
 104         timeout = 1000*conf->timeout;
 105         attempts = conf->attempts;
 106
 107         for (nns=0; nns<conf->nns; nns++) {
 108                 const struct address *iplit = &conf->ns[nns];
 109                 if (iplit->family == AF_INET) {
 110                         memcpy(&ns[nns].sin.sin_addr, iplit->addr, 4);
 111                         ns[nns].sin.sin_port = htons(53);
 112                         ns[nns].sin.sin_family = AF_INET;
 113                 } else {
 114                         sl = sizeof sa.sin6;
 115                         memcpy(&ns[nns].sin6.sin6_addr, iplit->addr, 16);
 116                         ns[nns].sin6.sin6_port = htons(53);
 117                         ns[nns].sin6.sin6_scope_id = iplit->scopeid;
 118                         ns[nns].sin6.sin6_family = family = AF_INET6;
 119                 }
 120         }
 121
 122         /* Get local address and open/bind a socket */
 123         fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 124
 125         /* Handle case where system lacks IPv6 support */
 126         if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
 127                 for (i=0; i<nns && conf->ns[nns].family == AF_INET6; i++);
 128                 if (i==nns) {
 129                         pthread_setcancelstate(cs, 0);
 130                         return -1;
 131                 }
 132                 fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 133                 family = AF_INET;
 134                 sl = sizeof sa.sin;
 135         }
 136
 137         /* Convert any IPv4 addresses in a mixed environment to v4-mapped */
 138         if (fd >= 0 && family == AF_INET6) {
 139                 setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
 140                 for (i=0; i<nns; i++) {
 141                         if (ns[i].sin.sin_family != AF_INET) continue;
 142                         memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
 143                                 &ns[i].sin.sin_addr, 4);
 144                         memcpy(ns[i].sin6.sin6_addr.s6_addr,
 145                                 "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
 146                         ns[i].sin6.sin6_family = AF_INET6;
 147                         ns[i].sin6.sin6_flowinfo = 0;
 148                         ns[i].sin6.sin6_scope_id = 0;
 149                 }
 150         }
 151
 152         sa.sin.sin_family = family;
 153         if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) {
 154                 if (fd >= 0) close(fd);
 155                 pthread_setcancelstate(cs, 0);
 156                 return -1;
 157         }
 158
 159         /* Past this point, there are no errors. Each individual query will
 160          * yield either no reply (indicated by zero length) or an answer
 161          * packet which is up to the caller to interpret. */
 162
 163         for (i=0; i<nqueries; i++) pfd[i].fd = -1;
 164         pfd[nqueries].fd = fd;
 165         pfd[nqueries].events = POLLIN;
 166         pfd[nqueries+1].fd = -2;
 167
 168         pthread_cleanup_push(cleanup, pfd);
 169         pthread_setcancelstate(cs, 0);
 170
 171         memset(alens, 0, sizeof *alens * nqueries);
 172
 173         retry_interval = timeout / attempts;
 174         next = 0;
 175         t0 = t2 = mtime();
 176         t1 = t2 - retry_interval;
 177
 178         for (; t2-t0 < timeout; t2=mtime()) {
 179                 /* This is the loop exit condition: that all queries
 180                  * have an accepted answer. */
 181                 for (i=0; i<nqueries && alens[i]>0; i++);
 182                 if (i==nqueries) break;
 183
 184                 if (t2-t1 >= retry_interval) {
 185                         /* Query all configured namservers in parallel */
 186                         for (i=0; i<nqueries; i++)
 187                                 if (!alens[i])
 188                                         for (j=0; j<nns; j++)
 189                                                 sendto(fd, queries[i],
 190                                                         qlens[i], MSG_NOSIGNAL,
 191                                                         (void *)&ns[j], sl);
 192                         t1 = t2;
 193                         servfail_retry = 2 * nqueries;
 194                 }
 195
 196                 /* Wait for a response, or until time to retry */
 197                 if (poll(pfd, nqueries+1, t1+retry_interval-t2) <= 0) continue;
 198
 199                 while (next < nqueries) {
 200                         struct msghdr mh = {
 201                                 .msg_name = (void *)&sa,
 202                                 .msg_namelen = sl,
 203                                 .msg_iovlen = 1,
 204                                 .msg_iov = (struct iovec []){
 205                                         { .iov_base = (void *)answers[next],
 206                                           .iov_len = asize }
 207                                 }
 208                         };
 209                         rlen = recvmsg(fd, &mh, 0);
 210                         if (rlen < 0) break;
 211
 212                         /* Ignore non-identifiable packets */
 213                         if (rlen < 4) continue;
 214
 215                         /* Ignore replies from addresses we didn't send to */
 216                         for (j=0; j<nns && memcmp(ns+j, &sa, sl); j++);
 217                         if (j==nns) continue;
 218
 219                         /* Find which query this answer goes with, if any */
 220                         for (i=next; i<nqueries && (
 221                                 answers[next][0] != queries[i][0] ||
 222                                 answers[next][1] != queries[i][1] ); i++);
 223                         if (i==nqueries) continue;
 224                         if (alens[i]) continue;
 225
 226                         /* Only accept positive or negative responses;
 227                          * retry immediately on server failure, and ignore
 228                          * all other codes such as refusal. */
 229                         switch (answers[next][3] & 15) {
 230                         case 0:
 231                         case 3:
 232                                 break;
 233                         case 2:
 234                                 if (servfail_retry && servfail_retry--)
 235                                         sendto(fd, queries[i],
 236                                                 qlens[i], MSG_NOSIGNAL,
 237                                                 (void *)&ns[j], sl);
 238                         default:
 239                                 continue;
 240                         }
 241
 242                         /* Store answer in the right slot, or update next
 243                          * available temp slot if it's already in place. */
 244                         alens[i] = rlen;
 245                         if (i == next)
 246                                 for (; next<nqueries && alens[next]; next++);
 247                         else
 248                                 memcpy(answers[i], answers[next], rlen);
 249
 250                         /* Ignore further UDP if all slots full or TCP-mode */
 251                         if (next == nqueries) pfd[nqueries].events = 0;
 252
 253                         /* If answer is truncated (TC bit), fallback to TCP */
 254                         if ((answers[i][2] & 2) || (mh.msg_flags & MSG_TRUNC)) {
 255                                 alens[i] = -1;
 256                                 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
 257                                 r = start_tcp(pfd+i, family, ns+j, sl, queries[i], qlens[i]);
 258                                 pthread_setcancelstate(cs, 0);
 259                                 if (r >= 0) {
 260                                         qpos[i] = r;
 261                                         apos[i] = 0;
 262                                 }
 263                                 continue;
 264                         }
 265                 }
 266
 267                 for (i=0; i<nqueries; i++) if (pfd[i].revents & POLLOUT) {
 268                         struct msghdr mh = {
 269                                 .msg_iovlen = 2,
 270                                 .msg_iov = (struct iovec [2]){
 271                                         { .iov_base = (uint8_t[]){ qlens[i]>>8, qlens[i] }, .iov_len = 2 },
 272                                         { .iov_base = (void *)queries[i], .iov_len = qlens[i] } }
 273                         };
 274                         step_mh(&mh, qpos[i]);
 275                         r = sendmsg(pfd[i].fd, &mh, MSG_NOSIGNAL);
 276                         if (r < 0) goto out;
 277                         qpos[i] += r;
 278                         if (qpos[i] == qlens[i]+2)
 279                                 pfd[i].events = POLLIN;
 280                 }
 281
 282                 for (i=0; i<nqueries; i++) if (pfd[i].revents & POLLIN) {
 283                         struct msghdr mh = {
 284                                 .msg_iovlen = 2,
 285                                 .msg_iov = (struct iovec [2]){
 286                                         { .iov_base = alen_buf[i], .iov_len = 2 },
 287                                         { .iov_base = answers[i], .iov_len = asize } }
 288                         };
 289                         step_mh(&mh, apos[i]);
 290                         r = recvmsg(pfd[i].fd, &mh, 0);
 291                         if (r <= 0) goto out;
 292                         apos[i] += r;
 293                         if (apos[i] < 2) continue;
 294                         int alen = alen_buf[i][0]*256 + alen_buf[i][1];
 295                         if (alen < 13) goto out;
 296                         if (apos[i] < alen+2 && apos[i] < asize+2)
 297                                 continue;
 298                         int rcode = answers[i][3] & 15;
 299                         if (rcode != 0 && rcode != 3)
 300                                 goto out;
 301
 302                         /* Storing the length here commits the accepted answer.
 303                          * Immediately close TCP socket so as not to consume
 304                          * resources we no longer need. */
 305                         alens[i] = alen;
 306                         __syscall(SYS_close, pfd[i].fd);
 307                         pfd[i].fd = -1;
 308                 }
 309         }
 310 out:
 311         pthread_cleanup_pop(1);
 312
 313         /* Disregard any incomplete TCP results */
 314         for (i=0; i<nqueries; i++) if (alens[i]<0) alens[i] = 0;
 315
 316         return 0;
 317 }
 318
 319 int __res_msend(int nqueries, const unsigned char *const *queries,
 320         const int *qlens, unsigned char *const *answers, int *alens, int asize)
 321 {
 322         struct resolvconf conf;
 323         if (__get_resolv_conf(&conf, 0, 0) < 0) return -1;
 324         return __res_msend_rc(nqueries, queries, qlens, answers, alens, asize, &conf);
 325 }