1 /*
2  * Copyright (c) 2022 Stefan Sperling <stsp@openbsd.org>
3  * Copyright (c) 2015 Ted Unangst <tedu@openbsd.org>
4  *
5  * Permission to use, copy, modify, and distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 #include <sys/types.h>
19 #include <sys/socket.h>
20 #include <sys/queue.h>
21 #include <sys/uio.h>
22 
23 #include <errno.h>
24 #include <event.h>
25 #include <limits.h>
26 #include <pwd.h>
27 #include <grp.h>
28 #include <sha1.h>
29 #include <sha2.h>
30 #include <signal.h>
31 #include <stdint.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <imsg.h>
36 #include <unistd.h>
37 
38 #include "got_error.h"
39 #include "got_path.h"
40 
41 #include "gotd.h"
42 #include "log.h"
43 #include "auth.h"
44 
45 static struct gotd_auth {
46 	pid_t pid;
47 	const char *title;
48 	struct gotd_repo *repo;
49 } gotd_auth;
50 
51 static void auth_shutdown(void);
52 
53 static void
54 auth_sighdlr(int sig, short event, void *arg)
55 {
56 	/*
57 	 * Normal signal handler rules don't apply because libevent
58 	 * decouples for us.
59 	 */
60 
61 	switch (sig) {
62 	case SIGHUP:
63 		break;
64 	case SIGUSR1:
65 		break;
66 	case SIGTERM:
67 	case SIGINT:
68 		auth_shutdown();
69 		/* NOTREACHED */
70 		break;
71 	default:
72 		fatalx("unexpected signal");
73 	}
74 }
75 
76 int
77 gotd_auth_parseuid(const char *s, uid_t *uid)
78 {
79 	struct passwd *pw;
80 	const char *errstr;
81 
82 	if ((pw = getpwnam(s)) != NULL) {
83 		*uid = pw->pw_uid;
84 		if (*uid == UID_MAX)
85 			return -1;
86 		return 0;
87 	}
88 	*uid = strtonum(s, 0, UID_MAX - 1, &errstr);
89 	if (errstr)
90 		return -1;
91 	return 0;
92 }
93 
94 static int
95 uidcheck(const char *s, uid_t desired)
96 {
97 	uid_t uid;
98 
99 	if (gotd_auth_parseuid(s, &uid) != 0)
100 		return -1;
101 	if (uid != desired)
102 		return -1;
103 	return 0;
104 }
105 
106 static int
107 parsegid(const char *s, gid_t *gid)
108 {
109 	struct group *gr;
110 	const char *errstr;
111 
112 	if ((gr = getgrnam(s)) != NULL) {
113 		*gid = gr->gr_gid;
114 		if (*gid == GID_MAX)
115 			return -1;
116 		return 0;
117 	}
118 	*gid = strtonum(s, 0, GID_MAX - 1, &errstr);
119 	if (errstr)
120 		return -1;
121 	return 0;
122 }
123 
124 static int
125 match_identifier(const char *identifier, gid_t *groups, int ngroups,
126     uid_t euid, gid_t egid)
127 {
128 	int i;
129 
130 	if (identifier[0] == ':') {
131 		gid_t rgid;
132 		if (parsegid(identifier + 1, &rgid) == -1)
133 			return 0;
134 		if (rgid == egid)
135 			return 1;
136 		for (i = 0; i < ngroups; i++) {
137 			if (rgid == groups[i])
138 				break;
139 		}
140 		if (i == ngroups)
141 			return 0;
142 	} else if (uidcheck(identifier, euid) != 0)
143 		return 0;
144 
145 	return 1;
146 }
147 
148 static const struct got_error *
149 auth_check(struct gotd_access_rule_list *rules, const char *repo_name,
150     uid_t euid, gid_t egid, int required_auth)
151 {
152 	struct gotd_access_rule *rule;
153 	enum gotd_access access = GOTD_ACCESS_DENIED;
154 	struct passwd *pw;
155 	gid_t groups[NGROUPS_MAX];
156 	int ngroups = NGROUPS_MAX;
157 
158 	pw = getpwuid(euid);
159 	if (pw == NULL) {
160 		if (errno)
161 			return got_error_from_errno("getpwuid");
162 		else
163 			return got_error_set_errno(EACCES, repo_name);
164 	}
165 
166 	if (getgrouplist(pw->pw_name, pw->pw_gid, groups, &ngroups) == -1)
167 		log_warnx("group membership list truncated");
168 
169 	STAILQ_FOREACH(rule, rules, entry) {
170 		if (!match_identifier(rule->identifier, groups, ngroups,
171 		    euid, egid))
172 			continue;
173 
174 		access = rule->access;
175 		if (rule->access == GOTD_ACCESS_PERMITTED &&
176 		    (rule->authorization & required_auth) != required_auth)
177 			access = GOTD_ACCESS_DENIED;
178 	}
179 
180 	if (access == GOTD_ACCESS_DENIED)
181 		return got_error_set_errno(EACCES, repo_name);
182 
183 	if (access == GOTD_ACCESS_PERMITTED)
184 		return NULL;
185 
186 	/* should not happen, this would be a bug */
187 	return got_error_msg(GOT_ERR_NOT_IMPL, "bad access rule");
188 }
189 
190 static const struct got_error *
191 recv_authreq(struct imsg *imsg, struct gotd_imsgev *iev)
192 {
193 	const struct got_error *err;
194 	struct imsgbuf *ibuf = &iev->ibuf;
195 	struct gotd_imsg_auth iauth;
196 	size_t datalen;
197 	uid_t euid;
198 	gid_t egid;
199 
200 	log_debug("authentication request received");
201 
202 	datalen = imsg->hdr.len - IMSG_HEADER_SIZE;
203 	if (datalen != sizeof(iauth))
204 		return got_error(GOT_ERR_PRIVSEP_LEN);
205 
206 	memcpy(&iauth, imsg->data, datalen);
207 
208 	if (imsg->fd == -1)
209 		return got_error(GOT_ERR_PRIVSEP_NO_FD);
210 
211 	if (getpeereid(imsg->fd, &euid, &egid) == -1)
212 		return got_error_from_errno("getpeerid");
213 
214 	if (iauth.euid != euid)
215 		return got_error(GOT_ERR_UID);
216 	if (iauth.egid != egid)
217 		return got_error(GOT_ERR_GID);
218 
219 	log_debug("authenticating uid %d gid %d", euid, egid);
220 
221 	err = auth_check(&gotd_auth.repo->rules, gotd_auth.repo->name,
222 	    iauth.euid, iauth.egid, iauth.required_auth);
223 	if (err) {
224 		gotd_imsg_send_error(ibuf, PROC_AUTH, iauth.client_id, err);
225 		return err;
226 	}
227 
228 	if (gotd_imsg_compose_event(iev, GOTD_IMSG_ACCESS_GRANTED,
229 	    PROC_AUTH, -1, NULL, 0) == -1)
230 		return got_error_from_errno("imsg compose ACCESS_GRANTED");
231 
232 	return NULL;
233 }
234 
235 static void
236 auth_dispatch(int fd, short event, void *arg)
237 {
238 	const struct got_error *err = NULL;
239 	struct gotd_imsgev *iev = arg;
240 	struct imsgbuf *ibuf = &iev->ibuf;
241 	struct imsg imsg;
242 	ssize_t n;
243 	int shut = 0;
244 
245 	if (event & EV_READ) {
246 		if ((n = imsg_read(ibuf)) == -1 && errno != EAGAIN)
247 			fatal("imsg_read error");
248 		if (n == 0)	/* Connection closed. */
249 			shut = 1;
250 	}
251 
252 	if (event & EV_WRITE) {
253 		n = msgbuf_write(&ibuf->w);
254 		if (n == -1 && errno != EAGAIN)
255 			fatal("msgbuf_write");
256 		if (n == 0)	/* Connection closed. */
257 			shut = 1;
258 	}
259 
260 	for (;;) {
261 		if ((n = imsg_get(ibuf, &imsg)) == -1)
262 			fatal("%s: imsg_get", __func__);
263 		if (n == 0)	/* No more messages. */
264 			break;
265 
266 		switch (imsg.hdr.type) {
267 		case GOTD_IMSG_AUTHENTICATE:
268 			err = recv_authreq(&imsg, iev);
269 			if (err)
270 				log_warnx("%s: %s", gotd_auth.title, err->msg);
271 			break;
272 		default:
273 			log_debug("%s: unexpected imsg %d", gotd_auth.title,
274 			    imsg.hdr.type);
275 			break;
276 		}
277 
278 		imsg_free(&imsg);
279 	}
280 
281 	if (!shut) {
282 		gotd_imsg_event_add(iev);
283 	} else {
284 		/* This pipe is dead. Remove its event handler */
285 		event_del(&iev->ev);
286 		event_loopexit(NULL);
287 	}
288 }
289 
290 void
291 auth_main(const char *title, struct gotd_repolist *repos,
292     const char *repo_path)
293 {
294 	struct gotd_repo *repo = NULL;
295 	struct gotd_imsgev iev;
296 	struct event evsigint, evsigterm, evsighup, evsigusr1;
297 
298 	gotd_auth.title = title;
299 	gotd_auth.pid = getpid();
300 	TAILQ_FOREACH(repo, repos, entry) {
301 		if (got_path_cmp(repo->path, repo_path,
302 		    strlen(repo->path), strlen(repo_path)) == 0)
303 			break;
304 	}
305 	if (repo == NULL)
306 		fatalx("repository %s not found in config", repo_path);
307 	gotd_auth.repo = repo;
308 
309 	signal_set(&evsigint, SIGINT, auth_sighdlr, NULL);
310 	signal_set(&evsigterm, SIGTERM, auth_sighdlr, NULL);
311 	signal_set(&evsighup, SIGHUP, auth_sighdlr, NULL);
312 	signal_set(&evsigusr1, SIGUSR1, auth_sighdlr, NULL);
313 	signal(SIGPIPE, SIG_IGN);
314 
315 	signal_add(&evsigint, NULL);
316 	signal_add(&evsigterm, NULL);
317 	signal_add(&evsighup, NULL);
318 	signal_add(&evsigusr1, NULL);
319 
320 	imsg_init(&iev.ibuf, GOTD_FILENO_MSG_PIPE);
321 	iev.handler = auth_dispatch;
322 	iev.events = EV_READ;
323 	iev.handler_arg = NULL;
324 	event_set(&iev.ev, iev.ibuf.fd, EV_READ, auth_dispatch, &iev);
325 	if (event_add(&iev.ev, NULL) == -1)
326 		fatalx("event add");
327 
328 	event_dispatch();
329 
330 	auth_shutdown();
331 }
332 
333 static void
334 auth_shutdown(void)
335 {
336 	log_debug("%s: shutting down", gotd_auth.title);
337 	exit(0);
338 }