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shadow/src/newgrp.c

859 lines
24 KiB

/*
* SPDX-FileCopyrightText: 1990 - 1994, Julianne Frances Haugh
* SPDX-FileCopyrightText: 1996 - 2000, Marek Michałkiewicz
* SPDX-FileCopyrightText: 2001 - 2006, Tomasz Kłoczko
* SPDX-FileCopyrightText: 2007 - 2008, Nicolas François
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <config.h>
#ident "$Id$"
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <assert.h>
#include "defines.h"
#include "getdef.h"
#include "prototypes.h"
/*@-exitarg@*/
#include "exitcodes.h"
#include "shadowlog.h"
/*
* Global variables
*/
const char *Prog;
extern char **newenvp;
extern char **environ;
#ifdef HAVE_SETGROUPS
static int ngroups;
static /*@null@*/ /*@only@*/GETGROUPS_T *grouplist;
#endif
static bool is_newgrp;
#ifdef WITH_AUDIT
static char audit_buf[80];
#endif
/* local function prototypes */
static void usage (void);
static void check_perms (const struct group *grp,
struct passwd *pwd,
const char *groupname);
static void syslog_sg (const char *name, const char *group);
/*
* usage - print command usage message
*/
static void usage (void)
{
if (is_newgrp) {
(void) fputs (_("Usage: newgrp [-] [group]\n"), stderr);
} else {
(void) fputs (_("Usage: sg group [[-c] command]\n"), stderr);
}
}
static bool ingroup(const char *name, struct group *gr)
{
char **look;
bool notfound = true;
look = gr->gr_mem;
while (*look && notfound)
notfound = strcmp (*look++, name);
return !notfound;
}
/*
* find_matching_group - search all groups of a gr's group id for
* membership of a given username
* but check gr itself first
*/
static /*@null@*/struct group *find_matching_group (const char *name, struct group *gr)
{
gid_t gid = gr->gr_gid;
if (ingroup(name, gr))
return gr;
setgrent ();
while ((gr = getgrent ()) != NULL) {
if (gr->gr_gid != gid) {
continue;
}
/*
* A group with matching GID was found.
* Test for membership of 'name'.
*/
if (ingroup(name, gr))
break;
}
endgrent ();
return gr;
}
/*
* check_perms - check if the user is allowed to switch to this group
*
* If needed, the user will be authenticated.
*
* It will not return if the user could not be authenticated.
*/
static void check_perms (const struct group *grp,
struct passwd *pwd,
const char *groupname)
{
bool needspasswd = false;
struct spwd *spwd;
char *cp;
const char *cpasswd;
/*
* see if she is a member of this group (i.e. in the list of
* members of the group, or if the group is her primary group).
*
* If she isn't a member, she needs to provide the group password.
* If there is no group password, she will be denied access
* anyway.
*
*/
if ( (grp->gr_gid != pwd->pw_gid)
&& !is_on_list (grp->gr_mem, pwd->pw_name)) {
needspasswd = true;
}
/*
* If she does not have either a shadowed password, or a regular
* password, and the group has a password, she needs to give the
* group password.
*/
spwd = xgetspnam (pwd->pw_name);
if (NULL != spwd) {
pwd->pw_passwd = xstrdup (spwd->sp_pwdp);
spw_free (spwd);
}
if ((pwd->pw_passwd[0] == '\0') && (grp->gr_passwd[0] != '\0')) {
needspasswd = true;
}
/*
* Now I see about letting her into the group she requested. If she
* is the root user, I'll let her in without having to prompt for
* the password. Otherwise I ask for a password if she flunked one
* of the tests above.
*/
if ((getuid () != 0) && needspasswd) {
/*
* get the password from her, and set the salt for
* the decryption from the group file.
*/
cp = getpass (_("Password: "));
if (NULL == cp) {
goto failure;
}
/*
* encrypt the key she gave us using the salt from the
* password in the group file. The result of this encryption
* must match the previously encrypted value in the file.
*/
cpasswd = pw_encrypt (cp, grp->gr_passwd);
strzero (cp);
if (NULL == cpasswd) {
fprintf (stderr,
_("%s: failed to crypt password with previous salt: %s\n"),
Prog, strerror (errno));
SYSLOG ((LOG_INFO,
"Failed to crypt password with previous salt of group '%s'",
groupname));
goto failure;
}
if (grp->gr_passwd[0] == '\0' ||
strcmp (cpasswd, grp->gr_passwd) != 0) {
#ifdef WITH_AUDIT
snprintf (audit_buf, sizeof(audit_buf),
"authentication new-gid=%lu",
(unsigned long) grp->gr_gid);
audit_logger (AUDIT_GRP_AUTH, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
#endif
SYSLOG ((LOG_INFO,
"Invalid password for group '%s' from '%s'",
groupname, pwd->pw_name));
(void) sleep (1);
(void) fputs (_("Invalid password.\n"), stderr);
goto failure;
}
#ifdef WITH_AUDIT
snprintf (audit_buf, sizeof(audit_buf),
"authentication new-gid=%lu",
(unsigned long) grp->gr_gid);
audit_logger (AUDIT_GRP_AUTH, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 1);
#endif
}
return;
failure:
/* The closelog is probably unnecessary, but it does no
* harm. -- JWP
*/
closelog ();
#ifdef WITH_AUDIT
if (groupname) {
snprintf (audit_buf, sizeof(audit_buf),
"changing new-group=%s", groupname);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
} else {
audit_logger (AUDIT_CHGRP_ID, Prog,
"changing", NULL,
(unsigned int) getuid (), 0);
}
#endif
exit (EXIT_FAILURE);
}
#ifdef USE_SYSLOG
/*
* syslog_sg - log the change of group to syslog
*
* The logout will also be logged when the user will quit the
* sg/newgrp session.
*/
static void syslog_sg (const char *name, const char *group)
{
const char *loginname = getlogin ();
const char *tty = ttyname (0);
char *free_login = NULL, *free_tty = NULL;
if (loginname != NULL) {
free_login = xstrdup (loginname);
loginname = free_login;
}
if (tty != NULL) {
free_tty = xstrdup (tty);
tty = free_tty;
}
if (loginname == NULL) {
loginname = "???";
}
if (tty == NULL) {
tty = "???";
} else if (strncmp (tty, "/dev/", 5) == 0) {
tty += 5;
}
SYSLOG ((LOG_INFO,
"user '%s' (login '%s' on %s) switched to group '%s'",
name, loginname, tty, group));
#ifdef USE_PAM
/*
* We want to fork and exec the new shell in the child, leaving the
* parent waiting to log the session close.
*
* The parent must ignore signals generated from the console
* (SIGINT, SIGQUIT, SIGHUP) which might make the parent terminate
* before its child. When bash is exec'ed as the subshell, it
* generates a new process group id for itself, and consequently
* only SIGHUP, which is sent to all process groups in the session,
* can reach the parent. However, since arbitrary programs can be
* specified as login shells, there is no such guarantee in general.
* For the same reason, we must also ignore stop signals generated
* from the console (SIGTSTP, SIGTTIN, and SIGTTOU) in order to
* avoid any possibility of the parent being stopped when it
* receives SIGCHLD from the terminating subshell. -- JWP
*/
{
pid_t child;
/* Ignore these signals. The signal handlers will later be
* restored to the default handlers. */
(void) signal (SIGINT, SIG_IGN);
(void) signal (SIGQUIT, SIG_IGN);
(void) signal (SIGHUP, SIG_IGN);
(void) signal (SIGTSTP, SIG_IGN);
(void) signal (SIGTTIN, SIG_IGN);
(void) signal (SIGTTOU, SIG_IGN);
child = fork ();
if ((pid_t)-1 == child) {
/* error in fork() */
fprintf (stderr, _("%s: failure forking: %s\n"),
is_newgrp ? "newgrp" : "sg", strerror (errno));
#ifdef WITH_AUDIT
if (group) {
snprintf (audit_buf, sizeof(audit_buf),
"changing new-group=%s", group);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
} else {
audit_logger (AUDIT_CHGRP_ID, Prog,
"changing", NULL,
(unsigned int) getuid (), 0);
}
#endif
exit (EXIT_FAILURE);
} else if (child != 0) {
/* parent - wait for child to finish, then log session close */
int cst = 0;
gid_t gid = getgid();
struct group *grp = getgrgid (gid);
pid_t pid;
do {
errno = 0;
pid = waitpid (child, &cst, WUNTRACED);
if ((pid == child) && (WIFSTOPPED (cst) != 0)) {
/* The child (shell) was suspended.
* Suspend sg/newgrp. */
kill (getpid (), SIGSTOP);
/* wake child when resumed */
kill (child, SIGCONT);
}
} while ( ((pid == child) && (WIFSTOPPED (cst) != 0))
|| ((pid != child) && (errno == EINTR)));
/* local, no need for xgetgrgid */
if (NULL != grp) {
SYSLOG ((LOG_INFO,
"user '%s' (login '%s' on %s) returned to group '%s'",
name, loginname, tty, grp->gr_name));
} else {
SYSLOG ((LOG_INFO,
"user '%s' (login '%s' on %s) returned to group '%lu'",
name, loginname, tty,
(unsigned long) gid));
/* Either the user's passwd entry has a
* GID that does not match with any group,
* or the group was deleted while the user
* was in a newgrp session.*/
SYSLOG ((LOG_WARN,
"unknown GID '%lu' used by user '%s'",
(unsigned long) gid, name));
}
closelog ();
exit ((0 != WIFEXITED (cst)) ? WEXITSTATUS (cst)
: WTERMSIG (cst) + 128);
}
/* child - restore signals to their default state */
(void) signal (SIGINT, SIG_DFL);
(void) signal (SIGQUIT, SIG_DFL);
(void) signal (SIGHUP, SIG_DFL);
(void) signal (SIGTSTP, SIG_DFL);
(void) signal (SIGTTIN, SIG_DFL);
(void) signal (SIGTTOU, SIG_DFL);
}
#endif /* USE_PAM */
free(free_login);
free(free_tty);
}
#endif /* USE_SYSLOG */
/*
* newgrp - change the invokers current real and effective group id
*/
int main (int argc, char **argv)
{
bool initflag = false;
int i;
bool is_member = false;
bool cflag = false;
int err = 0;
gid_t gid;
char *cp;
const char *progbase;
const char *name, *prog;
char *group = NULL;
char *command = NULL;
char **envp = environ;
struct passwd *pwd;
/*@null@*/struct group *grp;
#ifdef SHADOWGRP
struct sgrp *sgrp;
#endif
#ifdef WITH_AUDIT
audit_help_open ();
#endif
(void) setlocale (LC_ALL, "");
(void) bindtextdomain (PACKAGE, LOCALEDIR);
(void) textdomain (PACKAGE);
/*
* Save my name for error messages and save my real gid incase of
* errors. If there is an error i have to exec a new login shell for
* the user since her old shell won't have fork'd to create the
* process. Skip over the program name to the next command line
* argument.
*
* This historical comment, and the code itself, suggest that the
* behavior of the system/shell on which it was written differed
* significantly from the one I am using. If this process was
* started from a shell (including the login shell), it was fork'ed
* and exec'ed as a child by that shell. In order to get the user
* back to that shell, it is only necessary to exit from this
* process which terminates the child of the fork. The parent shell,
* which is blocked waiting for a signal, will then receive a
* SIGCHLD and will continue; any changes made to the process
* persona or the environment after the fork never occurred in the
* parent process.
*
* Bottom line: we want to save the name and real gid for messages,
* but we do not need to restore the previous process persona and we
* don't need to re-exec anything. -- JWP
*/
Prog = Basename (argv[0]);
log_set_progname(Prog);
log_set_logfd(stderr);
is_newgrp = (strcmp (Prog, "newgrp") == 0);
OPENLOG (is_newgrp ? "newgrp" : "sg");
argc--;
argv++;
initenv ();
pwd = get_my_pwent ();
if (NULL == pwd) {
fprintf (stderr, _("%s: Cannot determine your user name.\n"),
Prog);
#ifdef WITH_AUDIT
audit_logger (AUDIT_CHGRP_ID, Prog,
"changing", NULL,
(unsigned int) getuid (), 0);
#endif
SYSLOG ((LOG_WARN, "Cannot determine the user name of the caller (UID %lu)",
(unsigned long) getuid ()));
closelog ();
exit (EXIT_FAILURE);
}
name = pwd->pw_name;
/*
* Parse the command line. There are two accepted flags. The first
* is "-", which for newgrp means to re-create the entire
* environment as though a login had been performed, and "-c", which
* for sg causes a command string to be executed.
*
* The next argument, if present, must be the new group name. Any
* remaining remaining arguments will be used to execute a command
* as the named group. If the group name isn't present, I just use
* the login group ID of the current user.
*
* The valid syntax are
* newgrp [-] [groupid]
* newgrp [-l] [groupid]
* sg [-]
* sg [-] groupid [[-c command]
*/
if ( (argc > 0)
&& ( (strcmp (argv[0], "-") == 0)
|| (strcmp (argv[0], "-l") == 0))) {
argc--;
argv++;
initflag = true;
}
if (!is_newgrp) {
/*
* Do the command line for everything that is
* not "newgrp".
*/
if ((argc > 0) && (argv[0][0] != '-')) {
group = argv[0];
argc--;
argv++;
} else {
usage ();
closelog ();
exit (EXIT_FAILURE);
}
if (argc > 0) {
/*
* skip -c if specified so both forms work:
* "sg group -c command" (as in the man page) or
* "sg group command" (as in the usage message).
*/
if ((argc > 1) && (strcmp (argv[0], "-c") == 0)) {
command = argv[1];
} else {
command = argv[0];
}
cflag = true;
}
} else {
/*
* Do the command line for "newgrp". It's just making sure
* there aren't any flags and getting the new group name.
*/
if ((argc > 0) && (argv[0][0] == '-')) {
usage ();
goto failure;
} else if (argv[0] != (char *) 0) {
group = argv[0];
} else {
/*
* get the group file entry for her login group id.
* the entry must exist, simply to be annoying.
*
* Perhaps in the past, but the default behavior now depends on the
* group entry, so it had better exist. -- JWP
*/
grp = xgetgrgid (pwd->pw_gid);
if (NULL == grp) {
fprintf (stderr,
_("%s: GID '%lu' does not exist\n"),
Prog, (unsigned long) pwd->pw_gid);
SYSLOG ((LOG_CRIT, "GID '%lu' does not exist",
(unsigned long) pwd->pw_gid));
goto failure;
} else {
group = grp->gr_name;
}
}
}
#ifdef HAVE_SETGROUPS
/*
* get the current users groupset. The new group will be added to
* the concurrent groupset if there is room, otherwise you get a
* nasty message but at least your real and effective group id's are
* set.
*/
/* don't use getgroups(0, 0) - it doesn't work on some systems */
i = 16;
for (;;) {
grouplist = (GETGROUPS_T *) xmalloc (i * sizeof (GETGROUPS_T));
ngroups = getgroups (i, grouplist);
if (i > ngroups && !(ngroups == -1 && errno == EINVAL)) {
break;
}
/* not enough room, so try allocating a larger buffer */
free (grouplist);
i *= 2;
}
if (ngroups < 0) {
perror ("getgroups");
#ifdef WITH_AUDIT
if (group) {
snprintf (audit_buf, sizeof(audit_buf),
"changing new-group=%s", group);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
} else {
audit_logger (AUDIT_CHGRP_ID, Prog,
"changing", NULL,
(unsigned int) getuid (), 0);
}
#endif
exit (EXIT_FAILURE);
}
#endif /* HAVE_SETGROUPS */
/*
* now we put her in the new group. The password file entry for her
* current user id has been gotten. If there was no optional group
* argument she will have her real and effective group id set to the
* set to the value from her password file entry.
*
* If run as newgrp, or as sg with no command, this process exec's
* an interactive subshell with the effective GID of the new group.
* If run as sg with a command, that command is exec'ed in this
* subshell. When this process terminates, either because the user
* exits, or the command completes, the parent of this process
* resumes with the current GID.
*
* If a group is explicitly specified on the command line, the
* interactive shell or command is run with that effective GID.
* Access will be denied if no entry for that group can be found in
* /etc/group. If the current user name appears in the members list
* for that group, access will be granted immediately; if not, the
* user will be challenged for that group's password. If the
* password response is incorrect, if the specified group does not
* have a password, or if that group has been locked by gpasswd -R,
* access will be denied. This is true even if the group specified
* has the user's login GID (as shown in /etc/passwd). If no group
* is explicitly specified on the command line, the effect is
* exactly the same as if a group name matching the user's login GID
* had been explicitly specified. Root, however, is never
* challenged for passwords, and is always allowed access.
*
* The previous behavior was to allow access to the login group if
* no explicit group was specified, irrespective of the group
* control file(s). This behavior is usually not desirable. A user
* wishing to return to the login group has only to exit back to the
* login shell. Generating yet more shell levels in order to
* provide a convenient "return" to the default group has the
* undesirable side effects of confusing the user, scrambling the
* history file, and consuming system resources. The default now is
* to lock out such behavior. A sys admin can allow it by explicitly
* including the user's name in the member list of the user's login
* group. -- JWP
*/
grp = getgrnam (group); /* local, no need for xgetgrnam */
if (NULL == grp) {
fprintf (stderr, _("%s: group '%s' does not exist\n"), Prog, group);
goto failure;
}
#ifdef HAVE_SETGROUPS
/* when using pam_group, she will not be listed in the groups
* database. However getgroups() will return the group. So
* if she is listed there already it is ok to grant membership.
*/
for (i = 0; i < ngroups; i++) {
if (grp->gr_gid == grouplist[i]) {
is_member = true;
break;
}
}
#endif /* HAVE_SETGROUPS */
/*
* For splitted groups (due to limitations of NIS), check all
* groups of the same GID like the requested group for
* membership of the current user.
*/
if (!is_member) {
grp = find_matching_group (name, grp);
if (NULL == grp) {
/*
* No matching group found. As we already know that
* the group exists, this happens only in the case
* of a requested group where the user is not member.
*
* Re-read the group entry for further processing.
*/
grp = xgetgrnam (group);
assert (NULL != grp);
}
}
#ifdef SHADOWGRP
sgrp = getsgnam (group);
if (NULL != sgrp) {
grp->gr_passwd = sgrp->sg_passwd;
grp->gr_mem = sgrp->sg_mem;
}
#endif
/*
* Check if the user is allowed to access this group.
*/
if (!is_member) {
check_perms (grp, pwd, group);
}
/*
* all successful validations pass through this point. The group id
* will be set, and the group added to the concurrent groupset.
*/
#ifdef USE_SYSLOG
if (getdef_bool ("SYSLOG_SG_ENAB")) {
syslog_sg (name, group);
}
#endif /* USE_SYSLOG */
gid = grp->gr_gid;
#ifdef HAVE_SETGROUPS
/*
* I am going to try to add her new group id to her concurrent group
* set. If the group id is already present i'll just skip this part.
* If the group doesn't fit, i'll complain loudly and skip this
* part.
*/
for (i = 0; i < ngroups; i++) {
if (gid == grouplist[i]) {
break;
}
}
if (i == ngroups) {
if (ngroups >= sysconf (_SC_NGROUPS_MAX)) {
(void) fputs (_("too many groups\n"), stderr);
} else {
grouplist[ngroups++] = gid;
if (setgroups (ngroups, grouplist) != 0) {
perror ("setgroups");
}
}
}
#endif
/*
* Close all files before changing the user/group IDs.
*
* The needed structure should have been copied before, or
* permission to read the database will be required.
*/
endspent ();
#ifdef SHADOWGRP
endsgent ();
#endif
endpwent ();
endgrent ();
/*
* Set the effective GID to the new group id and the effective UID
* to the real UID. For root, this also sets the real GID to the
* new group id.
*/
if (setgid (gid) != 0) {
perror ("setgid");
#ifdef WITH_AUDIT
snprintf (audit_buf, sizeof(audit_buf),
"changing new-gid=%lu", (unsigned long) gid);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
#endif
exit (EXIT_FAILURE);
}
if (setuid (getuid ()) != 0) {
perror ("setuid");
#ifdef WITH_AUDIT
snprintf (audit_buf, sizeof(audit_buf),
"changing new-gid=%lu", (unsigned long) gid);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
#endif
exit (EXIT_FAILURE);
}
/*
* See if the "-c" flag was used. If it was, i just create a shell
* command for her using the argument that followed the "-c" flag.
*/
if (cflag) {
closelog ();
execl (SHELL, "sh", "-c", command, (char *) 0);
#ifdef WITH_AUDIT
snprintf (audit_buf, sizeof(audit_buf),
"changing new-gid=%lu", (unsigned long) gid);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
#endif
perror (SHELL);
exit ((errno == ENOENT) ? E_CMD_NOTFOUND : E_CMD_NOEXEC);
}
/*
* I have to get the pathname of her login shell. As a favor, i'll
* try her environment for a $SHELL value first, and then try the
* password file entry. Obviously this shouldn't be in the
* restricted command directory since it could be used to leave the
* restricted environment.
*
* Note that the following assumes this user's entry in /etc/passwd
* does not have a chroot * prefix. If it does, the * will be copied
* verbatim into the exec path. This is probably not an issue
* because if this user is operating in a chroot jail, her entry in
* the version of /etc/passwd that is accessible here should
* probably never have a chroot shell entry (but entries for other
* users might). If I have missed something, and this causes you a
* problem, try using $SHELL as a workaround; also please notify me
* at jparmele@wildbear.com -- JWP
*/
cp = getenv ("SHELL");
if (!initflag && (NULL != cp)) {
prog = cp;
} else if ((NULL != pwd->pw_shell) && ('\0' != pwd->pw_shell[0])) {
prog = pwd->pw_shell;
} else {
prog = SHELL;
}
/*
* Now I try to find the basename of the login shell. This will
* become argv[0] of the spawned command.
*/
progbase = Basename (prog);
/*
* Switch back to her home directory if i am doing login
* initialization.
*/
if (initflag) {
if (chdir (pwd->pw_dir) != 0) {
perror ("chdir");
}
while (NULL != *envp) {
if (strncmp (*envp, "PATH=", 5) == 0 ||
strncmp (*envp, "HOME=", 5) == 0 ||
strncmp (*envp, "SHELL=", 6) == 0 ||
strncmp (*envp, "TERM=", 5) == 0)
addenv (*envp, NULL);
envp++;
}
} else {
while (NULL != *envp) {
addenv (*envp, NULL);
envp++;
}
}
#ifdef WITH_AUDIT
snprintf (audit_buf, sizeof(audit_buf), "changing new-gid=%lu",
(unsigned long) gid);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 1);
#endif
/*
* Exec the login shell and go away. We are trying to get back to
* the previous environment which should be the user's login shell.
*/
err = shell (prog, initflag ? (char *) 0 : progbase, newenvp);
exit ((err == ENOENT) ? E_CMD_NOTFOUND : E_CMD_NOEXEC);
/*@notreached@*/
failure:
/*
* The previous code, when run as newgrp, re-exec'ed the shell in
* the current process with the original gid on error conditions.
* See the comment above. This historical behavior now has the
* effect of creating unlogged extraneous shell layers when the
* command line has an error or there is an authentication failure.
* We now just want to exit with error status back to the parent
* process. The closelog is probably unnecessary, but it does no
* harm. -- JWP
*/
closelog ();
#ifdef WITH_AUDIT
if (NULL != group) {
snprintf (audit_buf, sizeof(audit_buf),
"changing new-group=%s", group);
audit_logger (AUDIT_CHGRP_ID, Prog,
audit_buf, NULL,
(unsigned int) getuid (), 0);
} else {
audit_logger (AUDIT_CHGRP_ID, Prog,
"changing", NULL,
(unsigned int) getuid (), 0);
}
#endif
exit (EXIT_FAILURE);
}