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 static int
77 uidcheck(const char *s, uid_t desired)
78 {
79 	uid_t uid;
80 
81 	if (gotd_parseuid(s, &uid) != 0)
82 		return -1;
83 	if (uid != desired)
84 		return -1;
85 	return 0;
86 }
87 
88 static int
89 parsegid(const char *s, gid_t *gid)
90 {
91 	struct group *gr;
92 	const char *errstr;
93 
94 	if ((gr = getgrnam(s)) != NULL) {
95 		*gid = gr->gr_gid;
96 		if (*gid == GID_MAX)
97 			return -1;
98 		return 0;
99 	}
100 	*gid = strtonum(s, 0, GID_MAX - 1, &errstr);
101 	if (errstr)
102 		return -1;
103 	return 0;
104 }
105 
106 static int
107 match_identifier(const char *identifier, gid_t *groups, int ngroups,
108     uid_t euid, gid_t egid)
109 {
110 	int i;
111 
112 	if (identifier[0] == ':') {
113 		gid_t rgid;
114 		if (parsegid(identifier + 1, &rgid) == -1)
115 			return 0;
116 		if (rgid == egid)
117 			return 1;
118 		for (i = 0; i < ngroups; i++) {
119 			if (rgid == groups[i])
120 				break;
121 		}
122 		if (i == ngroups)
123 			return 0;
124 	} else if (uidcheck(identifier, euid) != 0)
125 		return 0;
126 
127 	return 1;
128 }
129 
130 static const struct got_error *
131 auth_check(struct gotd_access_rule_list *rules, const char *repo_name,
132     uid_t euid, gid_t egid, int required_auth)
133 {
134 	struct gotd_access_rule *rule;
135 	enum gotd_access access = GOTD_ACCESS_DENIED;
136 	struct passwd *pw;
137 	gid_t groups[NGROUPS_MAX];
138 	int ngroups = NGROUPS_MAX;
139 
140 	pw = getpwuid(euid);
141 	if (pw == NULL) {
142 		if (errno)
143 			return got_error_from_errno("getpwuid");
144 		else
145 			return got_error_set_errno(EACCES, repo_name);
146 	}
147 
148 	if (getgrouplist(pw->pw_name, pw->pw_gid, groups, &ngroups) == -1)
149 		log_warnx("group membership list truncated");
150 
151 	STAILQ_FOREACH(rule, rules, entry) {
152 		if (!match_identifier(rule->identifier, groups, ngroups,
153 		    euid, egid))
154 			continue;
155 
156 		access = rule->access;
157 		if (rule->access == GOTD_ACCESS_PERMITTED &&
158 		    (rule->authorization & required_auth) != required_auth)
159 			access = GOTD_ACCESS_DENIED;
160 	}
161 
162 	if (access == GOTD_ACCESS_DENIED)
163 		return got_error_set_errno(EACCES, repo_name);
164 
165 	if (access == GOTD_ACCESS_PERMITTED)
166 		return NULL;
167 
168 	/* should not happen, this would be a bug */
169 	return got_error_msg(GOT_ERR_NOT_IMPL, "bad access rule");
170 }
171 
172 static const struct got_error *
173 recv_authreq(struct imsg *imsg, struct gotd_imsgev *iev)
174 {
175 	const struct got_error *err;
176 	struct imsgbuf *ibuf = &iev->ibuf;
177 	struct gotd_imsg_auth iauth;
178 	size_t datalen;
179 	uid_t euid;
180 	gid_t egid;
181 
182 	log_debug("authentication request received");
183 
184 	datalen = imsg->hdr.len - IMSG_HEADER_SIZE;
185 	if (datalen != sizeof(iauth))
186 		return got_error(GOT_ERR_PRIVSEP_LEN);
187 
188 	memcpy(&iauth, imsg->data, datalen);
189 
190 	if (imsg->fd == -1)
191 		return got_error(GOT_ERR_PRIVSEP_NO_FD);
192 
193 	if (getpeereid(imsg->fd, &euid, &egid) == -1)
194 		return got_error_from_errno("getpeerid");
195 
196 	if (iauth.euid != euid)
197 		return got_error(GOT_ERR_UID);
198 	if (iauth.egid != egid)
199 		return got_error(GOT_ERR_GID);
200 
201 	log_debug("authenticating uid %d gid %d", euid, egid);
202 
203 	err = auth_check(&gotd_auth.repo->rules, gotd_auth.repo->name,
204 	    iauth.euid, iauth.egid, iauth.required_auth);
205 	if (err) {
206 		gotd_imsg_send_error(ibuf, PROC_AUTH, iauth.client_id, err);
207 		return err;
208 	}
209 
210 	if (gotd_imsg_compose_event(iev, GOTD_IMSG_ACCESS_GRANTED,
211 	    PROC_AUTH, -1, NULL, 0) == -1)
212 		return got_error_from_errno("imsg compose ACCESS_GRANTED");
213 
214 	return NULL;
215 }
216 
217 static void
218 auth_dispatch(int fd, short event, void *arg)
219 {
220 	const struct got_error *err = NULL;
221 	struct gotd_imsgev *iev = arg;
222 	struct imsgbuf *ibuf = &iev->ibuf;
223 	struct imsg imsg;
224 	ssize_t n;
225 	int shut = 0;
226 
227 	if (event & EV_READ) {
228 		if ((n = imsg_read(ibuf)) == -1 && errno != EAGAIN)
229 			fatal("imsg_read error");
230 		if (n == 0)	/* Connection closed. */
231 			shut = 1;
232 	}
233 
234 	if (event & EV_WRITE) {
235 		n = msgbuf_write(&ibuf->w);
236 		if (n == -1 && errno != EAGAIN)
237 			fatal("msgbuf_write");
238 		if (n == 0)	/* Connection closed. */
239 			shut = 1;
240 	}
241 
242 	for (;;) {
243 		if ((n = imsg_get(ibuf, &imsg)) == -1)
244 			fatal("%s: imsg_get", __func__);
245 		if (n == 0)	/* No more messages. */
246 			break;
247 
248 		switch (imsg.hdr.type) {
249 		case GOTD_IMSG_AUTHENTICATE:
250 			err = recv_authreq(&imsg, iev);
251 			if (err)
252 				log_warnx("%s", err->msg);
253 			break;
254 		default:
255 			log_debug("unexpected imsg %d", imsg.hdr.type);
256 			break;
257 		}
258 
259 		imsg_free(&imsg);
260 	}
261 
262 	if (!shut) {
263 		gotd_imsg_event_add(iev);
264 	} else {
265 		/* This pipe is dead. Remove its event handler */
266 		event_del(&iev->ev);
267 		event_loopexit(NULL);
268 	}
269 }
270 
271 void
272 auth_main(const char *title, struct gotd_repolist *repos,
273     const char *repo_path)
274 {
275 	struct gotd_repo *repo = NULL;
276 	struct gotd_imsgev iev;
277 	struct event evsigint, evsigterm, evsighup, evsigusr1;
278 
279 	gotd_auth.title = title;
280 	gotd_auth.pid = getpid();
281 	TAILQ_FOREACH(repo, repos, entry) {
282 		if (got_path_cmp(repo->path, repo_path,
283 		    strlen(repo->path), strlen(repo_path)) == 0)
284 			break;
285 	}
286 	if (repo == NULL)
287 		fatalx("repository %s not found in config", repo_path);
288 	gotd_auth.repo = repo;
289 
290 	signal_set(&evsigint, SIGINT, auth_sighdlr, NULL);
291 	signal_set(&evsigterm, SIGTERM, auth_sighdlr, NULL);
292 	signal_set(&evsighup, SIGHUP, auth_sighdlr, NULL);
293 	signal_set(&evsigusr1, SIGUSR1, auth_sighdlr, NULL);
294 	signal(SIGPIPE, SIG_IGN);
295 
296 	signal_add(&evsigint, NULL);
297 	signal_add(&evsigterm, NULL);
298 	signal_add(&evsighup, NULL);
299 	signal_add(&evsigusr1, NULL);
300 
301 	imsg_init(&iev.ibuf, GOTD_FILENO_MSG_PIPE);
302 	iev.handler = auth_dispatch;
303 	iev.events = EV_READ;
304 	iev.handler_arg = NULL;
305 	event_set(&iev.ev, iev.ibuf.fd, EV_READ, auth_dispatch, &iev);
306 	if (event_add(&iev.ev, NULL) == -1)
307 		fatalx("event add");
308 
309 	event_dispatch();
310 
311 	auth_shutdown();
312 }
313 
314 static void
315 auth_shutdown(void)
316 {
317 	log_debug("shutting down");
318 	exit(0);
319 }