newgrp.c revision 231164 
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: stable/9/usr.bin/newgrp/newgrp.c 231164 2012-02-07 22:13:33Z delphij $");
33
34#include <sys/types.h>
35
36#include <err.h>
37#include <errno.h>
38#include <grp.h>
39#include <libgen.h>
40#include <limits.h>
41#include <login_cap.h>
42#include <paths.h>
43#include <pwd.h>
44#include <stdio.h>
45#include <stdlib.h>
46#include <string.h>
47#include <unistd.h>
48
49static void	 addgroup(const char *grpname);
50static void	 doshell(void);
51static int	 inarray(gid_t, const gid_t[], int);
52static void	 loginshell(void);
53static void	 restoregrps(void);
54static void	 usage(void);
55
56static struct passwd *pwd;
57static uid_t euid;
58
59extern char **environ;
60
61/* Manipulate effective user ID. */
62#define PRIV_START do {				\
63		if (seteuid(euid) < 0)		\
64			err(1, "seteuid");	\
65	} while (0)
66#define PRIV_END do {				\
67		if (seteuid(getuid()) < 0)	\
68			err(1, "seteuid");	\
69	} while (0)
70
71int
72main(int argc, char *argv[])
73{
74	int ch, login;
75
76	euid = geteuid();
77	if (seteuid(getuid()) < 0)
78		err(1, "seteuid");
79
80	if ((pwd = getpwuid(getuid())) == NULL)
81		errx(1, "unknown user");
82
83	login = 0;
84	while ((ch = getopt(argc, argv, "-l")) != -1) {
85		switch (ch) {
86		case '-':		/* Obsolescent */
87		case 'l':
88			login = 1;
89			break;
90		default:
91			usage();
92		}
93	}
94	argc -= optind;
95	argv += optind;
96
97	switch (argc) {
98	case 0:
99		restoregrps();
100		break;
101	case 1:
102		addgroup(*argv);
103		break;
104	default:
105		usage();
106	}
107
108	if (seteuid(euid) < 0)
109		err(1, "seteuid");
110	if (setuid(getuid()) < 0)
111		err(1, "setuid");
112
113	if (login)
114		loginshell();
115	else
116		doshell();
117
118	/*NOTREACHED*/
119	exit(1);
120}
121
122static void
123usage(void)
124{
125
126	fprintf(stderr, "usage: newgrp [-l] [group]\n");
127	exit(1);
128}
129
130static void
131restoregrps(void)
132{
133	int initres, setres;
134
135	PRIV_START;
136	initres = initgroups(pwd->pw_name, pwd->pw_gid);
137	setres = setgid(pwd->pw_gid);
138	PRIV_END;
139
140	if (initres < 0)
141		warn("initgroups");
142	if (setres < 0)
143		warn("setgid");
144}
145
146static void
147addgroup(const char *grpname)
148{
149	gid_t *grps;
150	long lgid, ngrps_max;
151	int dbmember, i, ngrps;
152	gid_t egid;
153	struct group *grp;
154	char *ep, *pass;
155	char **p;
156
157	egid = getegid();
158
159	/* Try it as a group name, then a group id. */
160	if ((grp = getgrnam(grpname)) == NULL)
161		if ((lgid = strtol(grpname, &ep, 10)) <= 0 || *ep != '\0' ||
162		    (grp = getgrgid((gid_t)lgid)) == NULL ) {
163			warnx("%s: bad group name", grpname);
164			return;
165		}
166
167	/*
168	 * If the user is not a member of the requested group and the group
169	 * has a password, prompt and check it.
170	 */
171	dbmember = 0;
172	if (pwd->pw_gid == grp->gr_gid)
173		dbmember = 1;
174	for (p = grp->gr_mem; *p != NULL; p++)
175		if (strcmp(*p, pwd->pw_name) == 0) {
176			dbmember = 1;
177			break;
178		}
179	if (!dbmember && *grp->gr_passwd != '\0' && getuid() != 0) {
180		pass = getpass("Password:");
181		if (pass == NULL ||
182		    strcmp(grp->gr_passwd, crypt(pass, grp->gr_passwd)) != 0) {
183			fprintf(stderr, "Sorry\n");
184			return;
185		}
186	}
187
188	ngrps_max = sysconf(_SC_NGROUPS_MAX) + 1;
189	if ((grps = malloc(sizeof(gid_t) * ngrps_max)) == NULL)
190		err(1, "malloc");
191	if ((ngrps = getgroups(ngrps_max, (gid_t *)grps)) < 0) {
192		warn("getgroups");
193		return;
194	}
195
196	/* Remove requested gid from supp. list if it exists. */
197	if (grp->gr_gid != egid && inarray(grp->gr_gid, grps, ngrps)) {
198		for (i = 0; i < ngrps; i++)
199			if (grps[i] == grp->gr_gid)
200				break;
201		ngrps--;
202		memmove(&grps[i], &grps[i + 1], (ngrps - i) * sizeof(gid_t));
203		PRIV_START;
204		if (setgroups(ngrps, (const gid_t *)grps) < 0) {
205			PRIV_END;
206			warn("setgroups");
207			return;
208		}
209		PRIV_END;
210	}
211
212	PRIV_START;
213	if (setgid(grp->gr_gid)) {
214		PRIV_END;
215		warn("setgid");
216		return;
217	}
218	PRIV_END;
219	grps[0] = grp->gr_gid;
220
221	/* Add old effective gid to supp. list if it does not exist. */
222	if (egid != grp->gr_gid && !inarray(egid, grps, ngrps)) {
223		if (ngrps == ngrps_max)
224			warnx("too many groups");
225		else {
226			grps[ngrps++] = egid;
227			PRIV_START;
228			if (setgroups(ngrps, (const gid_t *)grps)) {
229				PRIV_END;
230				warn("setgroups");
231				return;
232			}
233			PRIV_END;
234		}
235	}
236
237	free(grps);
238}
239
240static int
241inarray(gid_t gid, const gid_t grps[], int ngrps)
242{
243	int i;
244
245	for (i = 0; i < ngrps; i++)
246		if (grps[i] == gid)
247			return (1);
248	return (0);
249}
250
251/*
252 * Set the environment to what would be expected if the user logged in
253 * again; this performs the same steps as su(1)'s -l option.
254 */
255static void
256loginshell(void)
257{
258	char *args[2], **cleanenv, *term, *ticket;
259	const char *shell;
260	login_cap_t *lc;
261
262	shell = pwd->pw_shell;
263	if (*shell == '\0')
264		shell = _PATH_BSHELL;
265	if (chdir(pwd->pw_dir) < 0) {
266		warn("%s", pwd->pw_dir);
267		chdir("/");
268	}
269
270	term = getenv("TERM");
271	ticket = getenv("KRBTKFILE");
272
273	if ((cleanenv = calloc(20, sizeof(char *))) == NULL)
274		err(1, "calloc");
275	*cleanenv = NULL;
276	environ = cleanenv;
277
278	lc = login_getpwclass(pwd);
279	setusercontext(lc, pwd, pwd->pw_uid,
280	    LOGIN_SETPATH|LOGIN_SETUMASK|LOGIN_SETENV);
281	login_close(lc);
282	setenv("USER", pwd->pw_name, 1);
283	setenv("SHELL", shell, 1);
284	setenv("HOME", pwd->pw_dir, 1);
285	if (term != NULL)
286		setenv("TERM", term, 1);
287	if (ticket != NULL)
288		setenv("KRBTKFILE", ticket, 1);
289
290	if (asprintf(args, "-%s", basename(shell)) < 0)
291		err(1, "asprintf");
292	args[1] = NULL;
293
294	execv(shell, args);
295	err(1, "%s", shell);
296}
297
298static void
299doshell(void)
300{
301	const char *shell;
302
303	shell = pwd->pw_shell;
304	if (*shell == '\0')
305		shell = _PATH_BSHELL;
306	execl(shell, basename(shell), (char *)NULL);
307	err(1, "%s", shell);
308}
309