30c4fc7cf9
Document the need for the setuid bit and how to set it. Explain why it isn't set by default, and suggest simply adding users to groups instead. PR: docs/167741 MFC after: 3 weeks
312 lines
6.7 KiB
C
312 lines
6.7 KiB
C
/*-
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* Copyright (c) 2002 Tim J. Robbins.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* newgrp -- change to a new group
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <err.h>
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#include <errno.h>
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#include <grp.h>
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#include <libgen.h>
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#include <limits.h>
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#include <login_cap.h>
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#include <paths.h>
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#include <pwd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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static void addgroup(const char *grpname);
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static void doshell(void);
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static int inarray(gid_t, const gid_t[], int);
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static void loginshell(void);
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static void restoregrps(void);
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static void usage(void);
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static struct passwd *pwd;
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static uid_t euid;
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extern char **environ;
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/* Manipulate effective user ID. */
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#define PRIV_START do { \
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if (seteuid(euid) < 0) \
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err(1, "seteuid"); \
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} while (0)
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#define PRIV_END do { \
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if (seteuid(getuid()) < 0) \
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err(1, "seteuid"); \
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} while (0)
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int
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main(int argc, char *argv[])
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{
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int ch, login;
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if ((euid = geteuid()) != 0)
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warnx("need root permissions to function properly, check setuid bit");
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if (seteuid(getuid()) < 0)
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err(1, "seteuid");
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if ((pwd = getpwuid(getuid())) == NULL)
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errx(1, "unknown user");
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login = 0;
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while ((ch = getopt(argc, argv, "-l")) != -1) {
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switch (ch) {
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case '-': /* Obsolescent */
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case 'l':
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login = 1;
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break;
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default:
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usage();
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}
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}
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argc -= optind;
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argv += optind;
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switch (argc) {
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case 0:
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restoregrps();
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break;
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case 1:
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addgroup(*argv);
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break;
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default:
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usage();
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}
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if (seteuid(euid) < 0)
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err(1, "seteuid");
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if (setuid(getuid()) < 0)
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err(1, "setuid");
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if (login)
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loginshell();
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else
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doshell();
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/*NOTREACHED*/
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exit(1);
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}
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static void
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usage(void)
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{
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fprintf(stderr, "usage: newgrp [-l] [group]\n");
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exit(1);
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}
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static void
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restoregrps(void)
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{
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int initres, setres;
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PRIV_START;
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initres = initgroups(pwd->pw_name, pwd->pw_gid);
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setres = setgid(pwd->pw_gid);
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PRIV_END;
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if (initres < 0)
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warn("initgroups");
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if (setres < 0)
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warn("setgid");
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}
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static void
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addgroup(const char *grpname)
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{
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gid_t *grps;
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long lgid, ngrps_max;
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int dbmember, i, ngrps;
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gid_t egid;
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struct group *grp;
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char *ep, *pass, *cryptpw;
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char **p;
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egid = getegid();
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/* Try it as a group name, then a group id. */
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if ((grp = getgrnam(grpname)) == NULL)
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if ((lgid = strtol(grpname, &ep, 10)) <= 0 || *ep != '\0' ||
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(grp = getgrgid((gid_t)lgid)) == NULL ) {
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warnx("%s: bad group name", grpname);
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return;
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}
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/*
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* If the user is not a member of the requested group and the group
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* has a password, prompt and check it.
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*/
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dbmember = 0;
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if (pwd->pw_gid == grp->gr_gid)
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dbmember = 1;
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for (p = grp->gr_mem; *p != NULL; p++)
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if (strcmp(*p, pwd->pw_name) == 0) {
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dbmember = 1;
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break;
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}
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if (!dbmember && *grp->gr_passwd != '\0' && getuid() != 0) {
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pass = getpass("Password:");
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if (pass == NULL)
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return;
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cryptpw = crypt(pass, grp->gr_passwd);
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if (cryptpw == NULL || strcmp(grp->gr_passwd, cryptpw) != 0) {
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fprintf(stderr, "Sorry\n");
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return;
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}
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}
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ngrps_max = sysconf(_SC_NGROUPS_MAX) + 1;
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if ((grps = malloc(sizeof(gid_t) * ngrps_max)) == NULL)
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err(1, "malloc");
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if ((ngrps = getgroups(ngrps_max, (gid_t *)grps)) < 0) {
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warn("getgroups");
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goto end;
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}
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/* Remove requested gid from supp. list if it exists. */
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if (grp->gr_gid != egid && inarray(grp->gr_gid, grps, ngrps)) {
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for (i = 0; i < ngrps; i++)
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if (grps[i] == grp->gr_gid)
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break;
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ngrps--;
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memmove(&grps[i], &grps[i + 1], (ngrps - i) * sizeof(gid_t));
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PRIV_START;
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if (setgroups(ngrps, (const gid_t *)grps) < 0) {
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PRIV_END;
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warn("setgroups");
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goto end;
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}
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PRIV_END;
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}
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PRIV_START;
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if (setgid(grp->gr_gid)) {
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PRIV_END;
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warn("setgid");
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goto end;
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}
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PRIV_END;
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grps[0] = grp->gr_gid;
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/* Add old effective gid to supp. list if it does not exist. */
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if (egid != grp->gr_gid && !inarray(egid, grps, ngrps)) {
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if (ngrps == ngrps_max)
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warnx("too many groups");
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else {
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grps[ngrps++] = egid;
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PRIV_START;
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if (setgroups(ngrps, (const gid_t *)grps)) {
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PRIV_END;
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warn("setgroups");
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goto end;
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}
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PRIV_END;
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}
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}
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end:
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free(grps);
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}
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static int
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inarray(gid_t gid, const gid_t grps[], int ngrps)
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{
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int i;
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for (i = 0; i < ngrps; i++)
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if (grps[i] == gid)
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return (1);
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return (0);
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}
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/*
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* Set the environment to what would be expected if the user logged in
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* again; this performs the same steps as su(1)'s -l option.
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*/
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static void
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loginshell(void)
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{
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char *args[2], **cleanenv, *term, *ticket;
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const char *shell;
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login_cap_t *lc;
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shell = pwd->pw_shell;
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if (*shell == '\0')
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shell = _PATH_BSHELL;
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if (chdir(pwd->pw_dir) < 0) {
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warn("%s", pwd->pw_dir);
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chdir("/");
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}
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term = getenv("TERM");
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ticket = getenv("KRBTKFILE");
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if ((cleanenv = calloc(20, sizeof(char *))) == NULL)
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err(1, "calloc");
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*cleanenv = NULL;
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environ = cleanenv;
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lc = login_getpwclass(pwd);
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setusercontext(lc, pwd, pwd->pw_uid,
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LOGIN_SETPATH|LOGIN_SETUMASK|LOGIN_SETENV);
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login_close(lc);
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setenv("USER", pwd->pw_name, 1);
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setenv("SHELL", shell, 1);
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setenv("HOME", pwd->pw_dir, 1);
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if (term != NULL)
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setenv("TERM", term, 1);
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if (ticket != NULL)
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setenv("KRBTKFILE", ticket, 1);
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if (asprintf(args, "-%s", basename(shell)) < 0)
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err(1, "asprintf");
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args[1] = NULL;
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execv(shell, args);
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err(1, "%s", shell);
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}
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static void
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doshell(void)
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{
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const char *shell;
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shell = pwd->pw_shell;
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if (*shell == '\0')
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shell = _PATH_BSHELL;
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execl(shell, basename(shell), (char *)NULL);
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err(1, "%s", shell);
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}
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