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1 /* darkstat 3
2 * copyright (c) 2001-2014 Emil Mikulic.
3 *
4 * dns.c: synchronous DNS in a child process.
5 *
6 * You may use, modify and redistribute this file under the terms of the
7 * GNU General Public License version 2. (see COPYING.GPL)
8 */
9
10 #include "cdefs.h"
11 #include "cap.h"
12 #include "conv.h"
13 #include "decode.h"
14 #include "dns.h"
15 #include "err.h"
16 #include "hosts_db.h"
17 #include "queue.h"
18 #include "str.h"
19 #include "tree.h"
20 #include "bsd.h" /* for setproctitle, strlcpy */
21
22 #include <sys/param.h>
23 #include <sys/socket.h>
24 #include <sys/wait.h>
25 #include <assert.h>
26 #include <errno.h>
27 #include <netdb.h>
28 #include <signal.h>
29 #include <stdlib.h>
30 #include <string.h>
31 #include <unistd.h>
32
33 #ifdef __NetBSD__
34 # define gethostbyaddr(addr, len, type) \
35 gethostbyaddr((const char *)(addr), len, type)
36 #endif
37
38 static void dns_main(void) _noreturn_; /* the child process runs this */
39
40 #define CHILD 0 /* child process uses this socket */
41 #define PARENT 1
42 static int dns_sock[2];
43 static pid_t pid = -1;
44
45 struct dns_reply {
46 struct addr addr;
47 int error; /* for gai_strerror(), or 0 if no error */
48 char name[256]; /* http://tools.ietf.org/html/rfc1034#section-3.1 */
49 };
50
51 void
52 dns_init(const char *privdrop_user)
53 {
54 if (socketpair(AF_UNIX, SOCK_STREAM, 0, dns_sock) == -1)
55 err(1, "socketpair");
56
57 pid = fork();
58 if (pid == -1)
59 err(1, "fork");
60
61 if (pid == 0) {
62 /* We are the child. */
63 privdrop(NULL /* don't chroot */, privdrop_user);
64 close(dns_sock[PARENT]);
65 dns_sock[PARENT] = -1;
66 daemonize_finish(); /* drop our copy of the lifeline! */
67 if (signal(SIGUSR1, SIG_IGN) == SIG_ERR)
68 errx(1, "signal(SIGUSR1, ignore) failed");
69 cap_free_args();
70 dns_main();
71 } else {
72 /* We are the parent. */
73 close(dns_sock[CHILD]);
74 dns_sock[CHILD] = -1;
75 fd_set_nonblock(dns_sock[PARENT]);
76 verbosef("DNS child has PID %d", pid);
77 }
78 }
79
80 void
81 dns_stop(void)
82 {
83 if (pid == -1)
84 return; /* no child was started */
85 close(dns_sock[PARENT]);
86 if (kill(pid, SIGINT) == -1)
87 err(1, "kill");
88 verbosef("dns_stop() waiting for child");
89 if (waitpid(pid, NULL, 0) == -1)
90 err(1, "waitpid");
91 verbosef("dns_stop() done waiting for child");
92 }
93
94 struct tree_rec {
95 RB_ENTRY(tree_rec) ptree;
96 struct addr ip;
97 };
98
99 static int
100 tree_cmp(struct tree_rec *a, struct tree_rec *b)
101 {
102 if (a->ip.family != b->ip.family)
103 /* Sort IPv4 to the left of IPv6. */
104 return ((a->ip.family == IPv4) ? -1 : +1);
105
106 if (a->ip.family == IPv4)
107 return (memcmp(&a->ip.ip.v4, &b->ip.ip.v4, sizeof(a->ip.ip.v4)));
108 else {
109 assert(a->ip.family == IPv6);
110 return (memcmp(&a->ip.ip.v6, &b->ip.ip.v6, sizeof(a->ip.ip.v6)));
111 }
112 }
113
114 static RB_HEAD(tree_t, tree_rec) ip_tree = RB_INITIALIZER(&tree_rec);
115 RB_GENERATE_STATIC(tree_t, tree_rec, ptree, tree_cmp)
116
117 void
118 dns_queue(const struct addr *const ipaddr)
119 {
120 struct tree_rec *rec;
121 ssize_t num_w;
122
123 if (pid == -1)
124 return; /* no child was started - we're not doing any DNS */
125
126 if ((ipaddr->family != IPv4) && (ipaddr->family != IPv6)) {
127 verbosef("dns_queue() for unknown family %d", ipaddr->family);
128 return;
129 }
130
131 rec = xmalloc(sizeof(*rec));
132 memcpy(&rec->ip, ipaddr, sizeof(rec->ip));
133
134 if (RB_INSERT(tree_t, &ip_tree, rec) != NULL) {
135 /* Already queued - this happens seldom enough that we don't care about
136 * the performance hit of needlessly malloc()ing. */
137 verbosef("already queued %s", addr_to_str(ipaddr));
138 free(rec);
139 return;
140 }
141
142 num_w = write(dns_sock[PARENT], ipaddr, sizeof(*ipaddr)); /* won't block */
143 if (num_w == 0)
144 warnx("dns_queue: write: ignoring end of file");
145 else if (num_w == -1)
146 warn("dns_queue: ignoring write error");
147 else if (num_w != sizeof(*ipaddr))
148 err(1, "dns_queue: wrote %zu instead of %zu", num_w, sizeof(*ipaddr));
149 }
150
151 static void
152 dns_unqueue(const struct addr *const ipaddr)
153 {
154 struct tree_rec tmp, *rec;
155
156 memcpy(&tmp.ip, ipaddr, sizeof(tmp.ip));
157 if ((rec = RB_FIND(tree_t, &ip_tree, &tmp)) != NULL) {
158 RB_REMOVE(tree_t, &ip_tree, rec);
159 free(rec);
160 }
161 else
162 verbosef("couldn't unqueue %s - not in queue!", addr_to_str(ipaddr));
163 }
164
165 /*
166 * Returns non-zero if result waiting, stores IP and name into given pointers
167 * (name buffer is allocated by dns_poll)
168 */
169 static int
170 dns_get_result(struct addr *ipaddr, char **name)
171 {
172 struct dns_reply reply;
173 ssize_t numread;
174
175 numread = read(dns_sock[PARENT], &reply, sizeof(reply));
176 if (numread == -1) {
177 if (errno == EAGAIN)
178 return (0); /* no input waiting */
179 else
180 goto error;
181 }
182 if (numread == 0)
183 goto error; /* EOF */
184 if (numread != sizeof(reply))
185 errx(1, "dns_get_result read got %zu, expected %zu",
186 numread, sizeof(reply));
187
188 /* Return successful reply. */
189 memcpy(ipaddr, &reply.addr, sizeof(*ipaddr));
190 if (reply.error != 0) {
191 /* Identify common special cases. */
192 const char *type = "none";
193
194 if (reply.addr.family == IPv6) {
195 if (IN6_IS_ADDR_LINKLOCAL(&reply.addr.ip.v6))
196 type = "link-local";
197 else if (IN6_IS_ADDR_SITELOCAL(&reply.addr.ip.v6))
198 type = "site-local";
199 else if (IN6_IS_ADDR_MULTICAST(&reply.addr.ip.v6))
200 type = "multicast";
201 } else {
202 assert(reply.addr.family == IPv4);
203 if (IN_MULTICAST(htonl(reply.addr.ip.v4)))
204 type = "multicast";
205 }
206 xasprintf(name, "(%s)", type);
207 }
208 else /* Correctly resolved name. */
209 *name = xstrdup(reply.name);
210
211 dns_unqueue(&reply.addr);
212 return (1);
213
214 error:
215 warn("dns_get_result: ignoring read error");
216 /* FIXME: re-align to stream? restart dns child? */
217 return (0);
218 }
219
220 void
221 dns_poll(void)
222 {
223 struct addr ip;
224 char *name;
225
226 if (pid == -1)
227 return; /* no child was started - we're not doing any DNS */
228
229 while (dns_get_result(&ip, &name)) {
230 /* push into hosts_db */
231 struct bucket *b = host_find(&ip);
232
233 if (b == NULL) {
234 verbosef("resolved %s to %s but it's not in the DB!",
235 addr_to_str(&ip), name);
236 return;
237 }
238 if (b->u.host.dns != NULL) {
239 verbosef("resolved %s to %s but it's already in the DB!",
240 addr_to_str(&ip), name);
241 return;
242 }
243 b->u.host.dns = name;
244 }
245 }
246
247 /* ------------------------------------------------------------------------ */
248
249 struct qitem {
250 STAILQ_ENTRY(qitem) entries;
251 struct addr ip;
252 };
253
254 static STAILQ_HEAD(qhead, qitem) queue = STAILQ_HEAD_INITIALIZER(queue);
255
256 static void
257 enqueue(const struct addr *const ip)
258 {
259 struct qitem *i;
260
261 i = xmalloc(sizeof(*i));
262 memcpy(&i->ip, ip, sizeof(i->ip));
263 STAILQ_INSERT_TAIL(&queue, i, entries);
264 verbosef("DNS: enqueued %s", addr_to_str(ip));
265 }
266
267 /* Return non-zero and populate <ip> pointer if queue isn't empty. */
268 static int
269 dequeue(struct addr *ip)
270 {
271 struct qitem *i;
272
273 i = STAILQ_FIRST(&queue);
274 if (i == NULL)
275 return (0);
276 STAILQ_REMOVE_HEAD(&queue, entries);
277 memcpy(ip, &i->ip, sizeof(*ip));
278 free(i);
279 verbosef("DNS: dequeued %s", addr_to_str(ip));
280 return 1;
281 }
282
283 static void
284 xwrite(const int d, const void *buf, const size_t nbytes)
285 {
286 ssize_t ret = write(d, buf, nbytes);
287
288 if (ret == -1)
289 err(1, "write");
290 if (ret != (ssize_t)nbytes)
291 err(1, "wrote %d bytes instead of all %d bytes", (int)ret, (int)nbytes);
292 }
293
294 static void
295 dns_main(void)
296 {
297 struct addr ip;
298
299 setproctitle("DNS child");
300 fd_set_nonblock(dns_sock[CHILD]);
301 verbosef("DNS child entering main DNS loop");
302 for (;;) {
303 int blocking;
304
305 if (STAILQ_EMPTY(&queue)) {
306 blocking = 1;
307 fd_set_block(dns_sock[CHILD]);
308 verbosef("entering blocking read loop");
309 } else {
310 blocking = 0;
311 fd_set_nonblock(dns_sock[CHILD]);
312 verbosef("non-blocking poll");
313 }
314 for (;;) {
315 /* While we have input to process... */
316 ssize_t numread = read(dns_sock[CHILD], &ip, sizeof(ip));
317 if (numread == 0)
318 exit(0); /* end of file, nothing more to do here. */
319 if (numread == -1) {
320 if (!blocking && (errno == EAGAIN))
321 break; /* ran out of input */
322 /* else error */
323 err(1, "DNS: read failed");
324 }
325 if (numread != sizeof(ip))
326 err(1, "DNS: read got %zu bytes, expecting %zu",
327 numread, sizeof(ip));
328 enqueue(&ip);
329 if (blocking) {
330 /* After one blocking read, become non-blocking so that when we
331 * run out of input we fall through to queue processing.
332 */
333 blocking = 0;
334 fd_set_nonblock(dns_sock[CHILD]);
335 }
336 }
337
338 /* Process queue. */
339 if (dequeue(&ip)) {
340 struct dns_reply reply;
341 struct sockaddr_in sin;
342 struct sockaddr_in6 sin6;
343 struct hostent *he;
344 char host[NI_MAXHOST];
345 int ret, flags;
346
347 reply.addr = ip;
348 flags = NI_NAMEREQD;
349 # ifdef NI_IDN
350 flags |= NI_IDN;
351 # endif
352 switch (ip.family) {
353 case IPv4:
354 sin.sin_family = AF_INET;
355 sin.sin_addr.s_addr = ip.ip.v4;
356 ret = getnameinfo((struct sockaddr *) &sin, sizeof(sin),
357 host, sizeof(host), NULL, 0, flags);
358 if (ret == EAI_FAMILY) {
359 verbosef("getnameinfo error %s, trying gethostbyname",
360 gai_strerror(ret));
361 he = gethostbyaddr(&sin.sin_addr.s_addr,
362 sizeof(sin.sin_addr.s_addr), sin.sin_family);
363 if (he == NULL) {
364 ret = EAI_FAIL;
365 verbosef("gethostbyname error %s", hstrerror(h_errno));
366 } else {
367 ret = 0;
368 strlcpy(host, he->h_name, sizeof(host));
369 }
370 }
371 break;
372 case IPv6:
373 sin6.sin6_family = AF_INET6;
374 memcpy(&sin6.sin6_addr, &ip.ip.v6, sizeof(sin6.sin6_addr));
375 ret = getnameinfo((struct sockaddr *) &sin6, sizeof(sin6),
376 host, sizeof(host), NULL, 0, flags);
377 break;
378 default:
379 errx(1, "unexpected ip.family = %d", ip.family);
380 }
381
382 if (ret != 0) {
383 reply.name[0] = '\0';
384 reply.error = ret;
385 } else {
386 assert(sizeof(reply.name) > sizeof(char *)); /* not just a ptr */
387 strlcpy(reply.name, host, sizeof(reply.name));
388 reply.error = 0;
389 }
390 fd_set_block(dns_sock[CHILD]);
391 xwrite(dns_sock[CHILD], &reply, sizeof(reply));
392 verbosef("DNS: %s is \"%s\".", addr_to_str(&reply.addr),
393 (ret == 0) ? reply.name : gai_strerror(ret));
394 }
395 }
396 }
397
398 /* vim:set ts=3 sw=3 tw=78 expandtab: */