newgrp.c revision 267654 
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: releng/9.3/usr.bin/newgrp/newgrp.c 253205 2013-07-11 12:47:06Z des $");
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	if ((euid = geteuid()) != 0)
77		warnx("need root permissions to function properly, check setuid bit");
78	if (seteuid(getuid()) < 0)
79		err(1, "seteuid");
80
81	if ((pwd = getpwuid(getuid())) == NULL)
82		errx(1, "unknown user");
83
84	login = 0;
85	while ((ch = getopt(argc, argv, "-l")) != -1) {
86		switch (ch) {
87		case '-':		/* Obsolescent */
88		case 'l':
89			login = 1;
90			break;
91		default:
92			usage();
93		}
94	}
95	argc -= optind;
96	argv += optind;
97
98	switch (argc) {
99	case 0:
100		restoregrps();
101		break;
102	case 1:
103		addgroup(*argv);
104		break;
105	default:
106		usage();
107	}
108
109	if (seteuid(euid) < 0)
110		err(1, "seteuid");
111	if (setuid(getuid()) < 0)
112		err(1, "setuid");
113
114	if (login)
115		loginshell();
116	else
117		doshell();
118
119	/*NOTREACHED*/
120	exit(1);
121}
122
123static void
124usage(void)
125{
126
127	fprintf(stderr, "usage: newgrp [-l] [group]\n");
128	exit(1);
129}
130
131static void
132restoregrps(void)
133{
134	int initres, setres;
135
136	PRIV_START;
137	initres = initgroups(pwd->pw_name, pwd->pw_gid);
138	setres = setgid(pwd->pw_gid);
139	PRIV_END;
140
141	if (initres < 0)
142		warn("initgroups");
143	if (setres < 0)
144		warn("setgid");
145}
146
147static void
148addgroup(const char *grpname)
149{
150	gid_t *grps;
151	long lgid, ngrps_max;
152	int dbmember, i, ngrps;
153	gid_t egid;
154	struct group *grp;
155	char *ep, *pass;
156	char **p;
157
158	egid = getegid();
159
160	/* Try it as a group name, then a group id. */
161	if ((grp = getgrnam(grpname)) == NULL)
162		if ((lgid = strtol(grpname, &ep, 10)) <= 0 || *ep != '\0' ||
163		    (grp = getgrgid((gid_t)lgid)) == NULL ) {
164			warnx("%s: bad group name", grpname);
165			return;
166		}
167
168	/*
169	 * If the user is not a member of the requested group and the group
170	 * has a password, prompt and check it.
171	 */
172	dbmember = 0;
173	if (pwd->pw_gid == grp->gr_gid)
174		dbmember = 1;
175	for (p = grp->gr_mem; *p != NULL; p++)
176		if (strcmp(*p, pwd->pw_name) == 0) {
177			dbmember = 1;
178			break;
179		}
180	if (!dbmember && *grp->gr_passwd != '\0' && getuid() != 0) {
181		pass = getpass("Password:");
182		if (pass == NULL ||
183		    strcmp(grp->gr_passwd, crypt(pass, grp->gr_passwd)) != 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		return;
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			return;
209		}
210		PRIV_END;
211	}
212
213	PRIV_START;
214	if (setgid(grp->gr_gid)) {
215		PRIV_END;
216		warn("setgid");
217		return;
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				return;
233			}
234			PRIV_END;
235		}
236	}
237
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", basename(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, basename(shell), (char *)NULL);
308	err(1, "%s", shell);
309}
310