1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2002 Tim J. Robbins.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29/*
30 * newgrp -- change to a new group
31 */
32
33#include <sys/types.h>
34
35#include <err.h>
36#include <errno.h>
37#include <grp.h>
38#include <limits.h>
39#include <login_cap.h>
40#include <paths.h>
41#include <pwd.h>
42#include <stdio.h>
43#include <stdlib.h>
44#include <string.h>
45#include <unistd.h>
46
47static void	 addgroup(const char *grpname);
48static void	 doshell(void);
49static int	 inarray(gid_t, const gid_t[], int);
50static void	 loginshell(void);
51static void	 restoregrps(void);
52static void	 usage(void);
53
54static struct passwd *pwd;
55static uid_t euid;
56
57extern char **environ;
58
59/* Manipulate effective user ID. */
60#define PRIV_START do {				\
61		if (seteuid(euid) < 0)		\
62			err(1, "seteuid");	\
63	} while (0)
64#define PRIV_END do {				\
65		if (seteuid(getuid()) < 0)	\
66			err(1, "seteuid");	\
67	} while (0)
68
69int
70main(int argc, char *argv[])
71{
72	int ch, login;
73
74	if ((euid = geteuid()) != 0)
75		warnx("need root permissions to function properly, check setuid bit");
76	if (seteuid(getuid()) < 0)
77		err(1, "seteuid");
78
79	if ((pwd = getpwuid(getuid())) == NULL)
80		errx(1, "unknown user");
81
82	login = 0;
83	while ((ch = getopt(argc, argv, "-l")) != -1) {
84		switch (ch) {
85		case '-':		/* Obsolescent */
86		case 'l':
87			login = 1;
88			break;
89		default:
90			usage();
91		}
92	}
93	argc -= optind;
94	argv += optind;
95
96	switch (argc) {
97	case 0:
98		restoregrps();
99		break;
100	case 1:
101		addgroup(*argv);
102		break;
103	default:
104		usage();
105	}
106
107	if (seteuid(euid) < 0)
108		err(1, "seteuid");
109	if (setuid(getuid()) < 0)
110		err(1, "setuid");
111
112	if (login)
113		loginshell();
114	else
115		doshell();
116
117	/*NOTREACHED*/
118	exit(1);
119}
120
121static void
122usage(void)
123{
124
125	fprintf(stderr, "usage: newgrp [-l] [group]\n");
126	exit(1);
127}
128
129static void
130restoregrps(void)
131{
132	int initres, setres;
133
134	PRIV_START;
135	initres = initgroups(pwd->pw_name, pwd->pw_gid);
136	setres = setgid(pwd->pw_gid);
137	PRIV_END;
138
139	if (initres < 0)
140		warn("initgroups");
141	if (setres < 0)
142		warn("setgid");
143}
144
145static void
146addgroup(const char *grpname)
147{
148	gid_t *grps;
149	long lgid, ngrps_max;
150	int dbmember, i, ngrps;
151	gid_t egid;
152	struct group *grp;
153	char *ep, *pass, *cryptpw;
154	char **p;
155
156	egid = getegid();
157
158	/* Try it as a group name, then a group id. */
159	if ((grp = getgrnam(grpname)) == NULL)
160		if ((lgid = strtol(grpname, &ep, 10)) <= 0 || *ep != '\0' ||
161		    (grp = getgrgid((gid_t)lgid)) == NULL ) {
162			warnx("%s: bad group name", grpname);
163			return;
164		}
165
166	/*
167	 * If the user is not a member of the requested group and the group
168	 * has a password, prompt and check it.
169	 */
170	dbmember = 0;
171	if (pwd->pw_gid == grp->gr_gid)
172		dbmember = 1;
173	for (p = grp->gr_mem; *p != NULL; p++)
174		if (strcmp(*p, pwd->pw_name) == 0) {
175			dbmember = 1;
176			break;
177		}
178	if (!dbmember && *grp->gr_passwd != '\0' && getuid() != 0) {
179		pass = getpass("Password:");
180		if (pass == NULL)
181			return;
182		cryptpw = crypt(pass, grp->gr_passwd);
183		if (cryptpw == NULL || strcmp(grp->gr_passwd, cryptpw) != 0) {
184			fprintf(stderr, "Sorry\n");
185			return;
186		}
187	}
188
189	ngrps_max = sysconf(_SC_NGROUPS_MAX) + 1;
190	if ((grps = malloc(sizeof(gid_t) * ngrps_max)) == NULL)
191		err(1, "malloc");
192	if ((ngrps = getgroups(ngrps_max, (gid_t *)grps)) < 0) {
193		warn("getgroups");
194		goto end;
195	}
196
197	/* Remove requested gid from supp. list if it exists. */
198	if (grp->gr_gid != egid && inarray(grp->gr_gid, grps, ngrps)) {
199		for (i = 0; i < ngrps; i++)
200			if (grps[i] == grp->gr_gid)
201				break;
202		ngrps--;
203		memmove(&grps[i], &grps[i + 1], (ngrps - i) * sizeof(gid_t));
204		PRIV_START;
205		if (setgroups(ngrps, (const gid_t *)grps) < 0) {
206			PRIV_END;
207			warn("setgroups");
208			goto end;
209		}
210		PRIV_END;
211	}
212
213	PRIV_START;
214	if (setgid(grp->gr_gid)) {
215		PRIV_END;
216		warn("setgid");
217		goto end;
218	}
219	PRIV_END;
220	grps[0] = grp->gr_gid;
221
222	/* Add old effective gid to supp. list if it does not exist. */
223	if (egid != grp->gr_gid && !inarray(egid, grps, ngrps)) {
224		if (ngrps == ngrps_max)
225			warnx("too many groups");
226		else {
227			grps[ngrps++] = egid;
228			PRIV_START;
229			if (setgroups(ngrps, (const gid_t *)grps)) {
230				PRIV_END;
231				warn("setgroups");
232				goto end;
233			}
234			PRIV_END;
235		}
236	}
237end:
238	free(grps);
239}
240
241static int
242inarray(gid_t gid, const gid_t grps[], int ngrps)
243{
244	int i;
245
246	for (i = 0; i < ngrps; i++)
247		if (grps[i] == gid)
248			return (1);
249	return (0);
250}
251
252/*
253 * Set the environment to what would be expected if the user logged in
254 * again; this performs the same steps as su(1)'s -l option.
255 */
256static void
257loginshell(void)
258{
259	char *args[2], **cleanenv, *term, *ticket;
260	const char *shell;
261	login_cap_t *lc;
262
263	shell = pwd->pw_shell;
264	if (*shell == '\0')
265		shell = _PATH_BSHELL;
266	if (chdir(pwd->pw_dir) < 0) {
267		warn("%s", pwd->pw_dir);
268		chdir("/");
269	}
270
271	term = getenv("TERM");
272	ticket = getenv("KRBTKFILE");
273
274	if ((cleanenv = calloc(20, sizeof(char *))) == NULL)
275		err(1, "calloc");
276	*cleanenv = NULL;
277	environ = cleanenv;
278
279	lc = login_getpwclass(pwd);
280	setusercontext(lc, pwd, pwd->pw_uid,
281	    LOGIN_SETPATH|LOGIN_SETUMASK|LOGIN_SETENV);
282	login_close(lc);
283	setenv("USER", pwd->pw_name, 1);
284	setenv("SHELL", shell, 1);
285	setenv("HOME", pwd->pw_dir, 1);
286	if (term != NULL)
287		setenv("TERM", term, 1);
288	if (ticket != NULL)
289		setenv("KRBTKFILE", ticket, 1);
290
291	if (asprintf(args, "-%s", shell) < 0)
292		err(1, "asprintf");
293	args[1] = NULL;
294
295	execv(shell, args);
296	err(1, "%s", shell);
297}
298
299static void
300doshell(void)
301{
302	const char *shell;
303
304	shell = pwd->pw_shell;
305	if (*shell == '\0')
306		shell = _PATH_BSHELL;
307	execl(shell, shell, (char *)NULL);
308	err(1, "%s", shell);
309}
310