newgrp.c revision 200420 
1/*-
2 * Copyright (c) 2002 Tim J. Robbins.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27/*
28 * newgrp -- change to a new group
29 */
30
31#include <sys/cdefs.h>
32__FBSDID("$FreeBSD: head/usr.bin/newgrp/newgrp.c 200420 2009-12-11 23:35:38Z delphij $");
33
34#include <sys/types.h>
35
36#include <err.h>
37#include <grp.h>
38#include <libgen.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	euid = geteuid();
75	if (seteuid(getuid()) < 0)
76		err(1, "seteuid");
77
78	if ((pwd = getpwuid(getuid())) == NULL)
79		errx(1, "unknown user");
80
81	login = 0;
82	while ((ch = getopt(argc, argv, "-l")) != -1) {
83		switch (ch) {
84		case '-':		/* Obsolescent */
85		case 'l':
86			login = 1;
87			break;
88		default:
89			usage();
90		}
91	}
92	argc -= optind;
93	argv += optind;
94
95	switch (argc) {
96	case 0:
97		restoregrps();
98		break;
99	case 1:
100		addgroup(*argv);
101		break;
102	default:
103		usage();
104	}
105
106	if (seteuid(euid) < 0)
107		err(1, "seteuid");
108	if (setuid(getuid()) < 0)
109		err(1, "setuid");
110
111	if (login)
112		loginshell();
113	else
114		doshell();
115
116	/*NOTREACHED*/
117	exit(1);
118}
119
120static void
121usage(void)
122{
123
124	fprintf(stderr, "usage: newgrp [-l] [group]\n");
125	exit(1);
126}
127
128static void
129restoregrps(void)
130{
131	int initres, setres;
132
133	PRIV_START;
134	initres = initgroups(pwd->pw_name, pwd->pw_gid);
135	setres = setgid(pwd->pw_gid);
136	PRIV_END;
137
138	if (initres < 0)
139		warn("initgroups");
140	if (setres < 0)
141		warn("setgroups");
142}
143
144static void
145addgroup(const char *grpname)
146{
147	gid_t *grps;
148	long lgid, ngrps_max;
149	int dbmember, i, ngrps;
150	gid_t egid;
151	struct group *grp;
152	char *ep, *pass;
153	char **p;
154
155	egid = getegid();
156
157	/* Try it as a group name, then a group id. */
158	if ((grp = getgrnam(grpname)) == NULL)
159		if ((lgid = strtol(grpname, &ep, 10)) <= 0 || *ep != '\0' ||
160		    (grp = getgrgid((gid_t)lgid)) == NULL ) {
161			warnx("%s: bad group name", grpname);
162			return;
163		}
164
165	/*
166	 * If the user is not a member of the requested group and the group
167	 * has a password, prompt and check it.
168	 */
169	dbmember = 0;
170	if (pwd->pw_gid == grp->gr_gid)
171		dbmember = 1;
172	for (p = grp->gr_mem; *p != NULL; p++)
173		if (strcmp(*p, pwd->pw_name) == 0) {
174			dbmember = 1;
175			break;
176		}
177	if (!dbmember && *grp->gr_passwd != '\0' && getuid() != 0) {
178		pass = getpass("Password:");
179		if (pass == NULL ||
180		    strcmp(grp->gr_passwd, crypt(pass, grp->gr_passwd)) != 0) {
181			fprintf(stderr, "Sorry\n");
182			return;
183		}
184	}
185
186	ngrps_max = sysconf(_SC_NGROUPS_MAX) + 1;
187	if ((grps = malloc(sizeof(gid_t) * ngrps_max)) == NULL)
188		err(1, "malloc");
189	if ((ngrps = getgroups(ngrps_max, (gid_t *)grps)) < 0) {
190		warn("getgroups");
191		return;
192	}
193
194	/* Remove requested gid from supp. list if it exists. */
195	if (grp->gr_gid != egid && inarray(grp->gr_gid, grps, ngrps)) {
196		for (i = 0; i < ngrps; i++)
197			if (grps[i] == grp->gr_gid)
198				break;
199		ngrps--;
200		memmove(&grps[i], &grps[i + 1], (ngrps - i) * sizeof(gid_t));
201		PRIV_START;
202		if (setgroups(ngrps, (const gid_t *)grps) < 0) {
203			PRIV_END;
204			warn("setgroups");
205			return;
206		}
207		PRIV_END;
208	}
209
210	PRIV_START;
211	if (setgid(grp->gr_gid)) {
212		PRIV_END;
213		warn("setgid");
214		return;
215	}
216	PRIV_END;
217	grps[0] = grp->gr_gid;
218
219	/* Add old effective gid to supp. list if it does not exist. */
220	if (egid != grp->gr_gid && !inarray(egid, grps, ngrps)) {
221		if (ngrps == ngrps_max)
222			warnx("too many groups");
223		else {
224			grps[ngrps++] = egid;
225			PRIV_START;
226			if (setgroups(ngrps, (const gid_t *)grps)) {
227				PRIV_END;
228				warn("setgroups");
229				return;
230			}
231			PRIV_END;
232		}
233	}
234
235	free(grps);
236}
237
238static int
239inarray(gid_t gid, const gid_t grps[], int ngrps)
240{
241	int i;
242
243	for (i = 0; i < ngrps; i++)
244		if (grps[i] == gid)
245			return (1);
246	return (0);
247}
248
249/*
250 * Set the environment to what would be expected if the user logged in
251 * again; this performs the same steps as su(1)'s -l option.
252 */
253static void
254loginshell(void)
255{
256	char *args[2], **cleanenv, *term, *ticket;
257	const char *shell;
258	login_cap_t *lc;
259
260	shell = pwd->pw_shell;
261	if (*shell == '\0')
262		shell = _PATH_BSHELL;
263	if (chdir(pwd->pw_dir) < 0) {
264		warn("%s", pwd->pw_dir);
265		chdir("/");
266	}
267
268	term = getenv("TERM");
269	ticket = getenv("KRBTKFILE");
270
271	if ((cleanenv = calloc(20, sizeof(char *))) == NULL)
272		err(1, "calloc");
273	*cleanenv = NULL;
274	environ = cleanenv;
275
276	lc = login_getpwclass(pwd);
277	setusercontext(lc, pwd, pwd->pw_uid,
278	    LOGIN_SETPATH|LOGIN_SETUMASK|LOGIN_SETENV);
279	login_close(lc);
280	setenv("USER", pwd->pw_name, 1);
281	setenv("SHELL", shell, 1);
282	setenv("HOME", pwd->pw_dir, 1);
283	if (term != NULL)
284		setenv("TERM", term, 1);
285	if (ticket != NULL)
286		setenv("KRBTKFILE", ticket, 1);
287
288	if (asprintf(args, "-%s", basename(shell)) < 0)
289		err(1, "asprintf");
290	args[1] = NULL;
291
292	execv(shell, args);
293	err(1, "%s", shell);
294}
295
296static void
297doshell(void)
298{
299	const char *shell;
300
301	shell = pwd->pw_shell;
302	if (*shell == '\0')
303		shell = _PATH_BSHELL;
304	execl(shell, basename(shell), (char *)NULL);
305	err(1, "%s", shell);
306}
307