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shadow/src/newgrp.c

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/*
* Copyright 1990 - 1994, Julianne Frances Haugh
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of Julianne F. Haugh nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <config.h>
#include "rcsid.h"
RCSID (PKG_VER "$Id: newgrp.c,v 1.35 2005/08/11 11:26:11 kloczek Exp $")
#include <stdio.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include "prototypes.h"
#include "defines.h"
#include "getdef.h"
extern char **environ;
#ifdef HAVE_SETGROUPS
static int ngroups;
static GETGROUPS_T *grouplist;
#endif
static char *Prog;
static int is_newgrp;
/* local function prototypes */
static void usage (void);
/*
* usage - print command usage message
*/
static void usage (void)
{
if (is_newgrp)
fprintf (stderr, _("Usage: newgrp [-] [group]\n"));
else
fprintf (stderr, _("Usage: sg group [[-c] command]\n"));
}
/*
* find_matching_group - search all groups of a given group id for
* membership of a given username
*/
static struct group *find_matching_group (const char *name, gid_t gid)
{
struct group *gr;
char **look;
int notfound = 1;
setgrent ();
while ((gr = getgrent ()) != NULL) {
if (gr->gr_gid != gid) {
continue;
}
/*
* A group with matching GID was found.
* Test for membership of 'name'.
*/
look = gr->gr_mem;
while (*look && (notfound = strcmp (*look++, name)));
if (!notfound)
break;
}
endgrent ();
return gr;
}
/*
* newgrp - change the invokers current real and effective group id
*/
int main (int argc, char **argv)
{
int initflag = 0;
int needspasswd = 0;
int i;
int cflag = 0;
gid_t gid;
char *cp;
const char *cpasswd, *name, *prog;
char *group = NULL;
char *command = NULL;
char **envp = environ;
struct passwd *pwd;
struct group *grp;
struct spwd *spwd;
#ifdef SHADOWGRP
struct sgrp *sgrp;
#endif
setlocale (LC_ALL, "");
bindtextdomain (PACKAGE, LOCALEDIR);
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]);
is_newgrp = (strcmp (Prog, "newgrp") == 0);
OPENLOG (is_newgrp ? "newgrp" : "sg");
gid = getgid ();
argc--;
argv++;
initenv ();
pwd = get_my_pwent ();
if (!pwd) {
fprintf (stderr, _("unknown UID: %u\n"), getuid ());
SYSLOG ((LOG_WARN, "unknown UID %u", getuid ()));
closelog ();
exit (1);
}
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], "-") || !strcmp (argv[0], "-l"))) {
argc--;
argv++;
initflag = 1;
}
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 (1);
}
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++;
}
} 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
*/
if (!(grp = getgrgid (pwd->pw_gid))) {
fprintf (stderr, _("unknown GID: %lu\n"),
(unsigned long) pwd->pw_gid);
SYSLOG ((LOG_CRIT, "unknown GID: %lu",
(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");
exit (1);
}
#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
*/
if (!(grp = getgrnam (group))) {
fprintf (stderr, _("unknown group: %s\n"), group);
goto failure;
}
/*
* 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.
*/
grp = find_matching_group (name, grp->gr_gid);
if (!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 = getgrnam (group);
}
#ifdef SHADOWGRP
if ((sgrp = getsgnam (group))) {
grp->gr_passwd = sgrp->sg_passwd;
grp->gr_mem = sgrp->sg_mem;
}
#endif
/*
* see if she is a member of this 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 (!is_on_list (grp->gr_mem, name))
needspasswd = 1;
/*
* 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.
*/
if ((spwd = getspnam (name)))
pwd->pw_passwd = spwd->sp_pwdp;
if (pwd->pw_passwd[0] == '\0' && grp->gr_passwd[0])
needspasswd = 1;
/*
* 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.
*
* Note that she now has to provide the password to her own group,
* unless she is listed as a member. -- JWP
*/
if (getuid () != 0 && needspasswd) {
/*
* get the password from her, and set the salt for
* the decryption from the group file.
*/
if (!(cp = getpass (_("Password: "))))
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 (grp->gr_passwd[0] == '\0') {
/*
* there is no password, print out "Sorry" and give up
*/
sleep (1);
fputs (_("Sorry.\n"), stderr);
goto failure;
}
if (strcmp (cpasswd, grp->gr_passwd) != 0) {
SYSLOG ((LOG_INFO,
"Invalid password for group `%s' from `%s'",
group, name));
sleep (1);
fputs (_("Sorry.\n"), stderr);
goto failure;
}
}
/*
* 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 ((LOG_INFO, "user `%s' switched to group `%s'",
name, group));
if (getdef_bool ("SYSLOG_SG_ENAB")) {
char *loginname = getlogin ();
char *tty = ttyname (0);
if (loginname != NULL)
loginname = xstrdup (loginname);
if (tty != NULL)
tty = xstrdup (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, pid;
signal (SIGINT, SIG_IGN);
signal (SIGQUIT, SIG_IGN);
signal (SIGHUP, SIG_IGN);
signal (SIGTSTP, SIG_IGN);
signal (SIGTTIN, SIG_IGN);
signal (SIGTTOU, SIG_IGN);
child = fork ();
if (child < 0) {
/* error in fork() */
fprintf (stderr, "%s: failure forking: %s",
is_newgrp ? "newgrp" : "sg", strerror (errno));
exit (1);
} else if (child) {
/* parent - wait for child to finish, then log session close */
do {
pid = waitpid (child, NULL, 0);
} while (pid != child);
SYSLOG ((LOG_INFO,
"user `%s' (login `%s' on %s) returned to group `%s'",
name, loginname, tty,
getgrgid (gid)->gr_name));
closelog ();
exit (0);
}
/* child - restore signals to their default state */
signal (SIGINT, SIG_DFL);
signal (SIGQUIT, SIG_DFL);
signal (SIGHUP, SIG_DFL);
signal (SIGTSTP, SIG_DFL);
signal (SIGTTIN, SIG_DFL);
signal (SIGTTOU, SIG_DFL);
#endif /* USE_PAM */
}
#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)) {
fprintf (stderr, _("too many groups\n"));
} else {
grouplist[ngroups++] = gid;
if (setgroups (ngroups, grouplist)) {
perror ("setgroups");
}
}
}
#endif
/*
* 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))
perror ("setgid");
if (setuid (getuid ())) {
perror ("setuid");
exit (1);
}
/*
* 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 ("/bin/sh", "sh", "-c", command, (char *) 0);
if (errno == ENOENT) {
perror ("/bin/sh");
exit (127);
} else {
perror ("/bin/sh");
exit (126);
}
}
/*
* 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
*/
if (!initflag && (cp = getenv ("SHELL")))
prog = cp;
else if (pwd->pw_shell && pwd->pw_shell[0])
prog = pwd->pw_shell;
else
prog = "/bin/sh";
/*
* Now i try to find the basename of the login shell. This will
* become argv[0] of the spawned command.
*/
cp = Basename ((char *) prog);
endspent ();
#ifdef SHADOWGRP
endsgent ();
#endif
endpwent ();
endgrent ();
/*
* Switch back to her home directory if i am doing login
* initialization.
*/
if (initflag) {
if (chdir (pwd->pw_dir))
perror ("chdir");
while (*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 (*envp)
addenv (*envp++, NULL);
}
/*
* 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.
*/
shell (prog, initflag ? (char *) 0 : cp);
/* 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 ();
exit (1);
}
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