su: move generic su code to su-common.c

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 883 insertions, 0 deletions

diff --git a/login-utils/su-common.c b/login-utils/su-common.c
new file mode 100644
index 000000000..4fc425055
--- /dev/null
+++ b/login-utils/su-common.c
@@ -0,0 +1,883 @@
+/* su for Linux.  Run a shell with substitute user and group IDs.
+   Copyright (C) 1992-2006 Free Software Foundation, Inc.
+   Copyright (C) 2012 SUSE Linux Products GmbH, Nuernberg
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Run a shell with the real and effective UID and GID and groups
+   of USER, default `root'.
+
+   The shell run is taken from USER's password entry, /bin/sh if
+   none is specified there.  If the account has a password, su
+   prompts for a password unless run by a user with real UID 0.
+
+   Does not change the current directory.
+   Sets `HOME' and `SHELL' from the password entry for USER, and if
+   USER is not root, sets `USER' and `LOGNAME' to USER.
+   The subshell is not a login shell.
+
+   If one or more ARGs are given, they are passed as additional
+   arguments to the subshell.
+
+   Does not handle /bin/sh or other shells specially
+   (setting argv[0] to "-su", passing -c only to certain shells, etc.).
+   I don't see the point in doing that, and it's ugly.
+
+   Based on an implemenation by David MacKenzie <djm@gnu.ai.mit.edu>.  */
+
+enum
+{
+  EXIT_CANNOT_INVOKE = 126,
+  EXIT_ENOENT = 127
+};
+
+#include <config.h>
+#include <stdio.h>
+#include <getopt.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <grp.h>
+#include <security/pam_appl.h>
+#include <security/pam_misc.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <syslog.h>
+
+#include "err.h"
+
+#include <stdbool.h>
+#include "c.h"
+#include "xalloc.h"
+#include "nls.h"
+#include "pathnames.h"
+#include "env.h"
+
+/* name of the pam configuration files. separate configs for su and su -  */
+#define PAM_SERVICE_NAME "su"
+#define PAM_SERVICE_NAME_L "su-l"
+
+#define is_pam_failure(_rc)	((_rc) != PAM_SUCCESS)
+
+#include "logindefs.h"
+#include "su-common.h"
+
+/* The shell to run if none is given in the user's passwd entry.  */
+#define DEFAULT_SHELL "/bin/sh"
+
+/* The user to become if none is specified.  */
+#define DEFAULT_USER "root"
+
+#ifndef HAVE_ENVIRON_DECL
+extern char **environ;
+#endif
+
+static void run_shell (char const *, char const *, char **, size_t)
+     __attribute__ ((__noreturn__));
+
+/* If true, pass the `-f' option to the subshell.  */
+static bool fast_startup;
+
+/* If true, simulate a login instead of just starting a shell.  */
+static bool simulate_login;
+
+/* If true, change some environment vars to indicate the user su'd to.  */
+static bool change_environment;
+
+/* If true, then don't call setsid() with a command. */
+static int same_session = 0;
+
+/* SU_MODE_{RUNUSER,SU} */
+static int su_mode;
+
+static bool _pam_session_opened;
+static bool _pam_cred_established;
+static sig_atomic_t volatile caught_signal = false;
+static pam_handle_t *pamh = NULL;
+
+static struct option const longopts[] =
+{
+  {"command", required_argument, NULL, 'c'},
+  {"session-command", required_argument, NULL, 'C'},
+  {"fast", no_argument, NULL, 'f'},
+  {"login", no_argument, NULL, 'l'},
+  {"preserve-environment", no_argument, NULL, 'p'},
+  {"shell", required_argument, NULL, 's'},
+  {"group", required_argument, NULL, 'g'},
+  {"supp-group", required_argument, NULL, 'G'},
+  {"help", no_argument, 0, 'h'},
+  {"version", no_argument, 0, 'V'},
+  {NULL, 0, NULL, 0}
+};
+
+/* Log the fact that someone has run su to the user given by PW;
+   if SUCCESSFUL is true, they gave the correct password, etc.  */
+
+static void
+log_su (struct passwd const *pw, bool successful)
+{
+  const char *new_user, *old_user, *tty;
+
+  new_user = pw->pw_name;
+  /* The utmp entry (via getlogin) is probably the best way to identify
+     the user, especially if someone su's from a su-shell.  */
+  old_user = getlogin ();
+  if (!old_user)
+    {
+      /* getlogin can fail -- usually due to lack of utmp entry.
+	 Resort to getpwuid.  */
+      struct passwd *pwd = getpwuid (getuid ());
+      old_user = (pwd ? pwd->pw_name : "");
+    }
+  tty = ttyname (STDERR_FILENO);
+  if (!tty)
+    tty = "none";
+
+  openlog (program_invocation_short_name, 0 , LOG_AUTH);
+  syslog (LOG_NOTICE, "%s(to %s) %s on %s",
+	  successful ? "" : "FAILED SU ",
+	  new_user, old_user, tty);
+  closelog ();
+}
+
+static struct pam_conv conv =
+{
+  misc_conv,
+  NULL
+};
+
+static void
+cleanup_pam (int retcode)
+{
+  int saved_errno = errno;
+
+  if (_pam_session_opened)
+    pam_close_session (pamh, 0);
+
+  if (_pam_cred_established)
+    pam_setcred (pamh, PAM_DELETE_CRED | PAM_SILENT);
+
+  pam_end(pamh, retcode);
+
+  errno = saved_errno;
+}
+
+/* Signal handler for parent process.  */
+static void
+su_catch_sig (int sig __attribute__((__unused__)))
+{
+  caught_signal = true;
+}
+
+/* Export env variables declared by PAM modules.  */
+static void
+export_pamenv (void)
+{
+  char **env;
+
+  /* This is a copy but don't care to free as we exec later anyways.  */
+  env = pam_getenvlist (pamh);
+  while (env && *env)
+    {
+      if (putenv (*env) != 0)
+	err (EXIT_FAILURE, NULL);
+      env++;
+    }
+}
+
+static void
+create_watching_parent (void)
+{
+  pid_t child;
+  sigset_t ourset;
+  int status = 0;
+  int retval;
+
+  retval = pam_open_session (pamh, 0);
+  if (is_pam_failure(retval))
+    {
+      cleanup_pam (retval);
+      errx (EXIT_FAILURE, _("cannot not open session: %s"),
+	     pam_strerror (pamh, retval));
+    }
+  else
+    _pam_session_opened = 1;
+
+  child = fork ();
+  if (child == (pid_t) -1)
+    {
+      cleanup_pam (PAM_ABORT);
+      err (EXIT_FAILURE, _("cannot create child process"));
+    }
+
+  /* the child proceeds to run the shell */
+  if (child == 0)
+    return;
+
+  /* In the parent watch the child.  */
+
+  /* su without pam support does not have a helper that keeps
+     sitting on any directory so let's go to /.  */
+  if (chdir ("/") != 0)
+    warn (_("cannot change directory to %s"), "/");
+
+  sigfillset (&ourset);
+  if (sigprocmask (SIG_BLOCK, &ourset, NULL))
+    {
+      warn (_("cannot block signals"));
+      caught_signal = true;
+    }
+  if (!caught_signal)
+    {
+      struct sigaction action;
+      action.sa_handler = su_catch_sig;
+      sigemptyset (&action.sa_mask);
+      action.sa_flags = 0;
+      sigemptyset (&ourset);
+    if (!same_session)
+      {
+        if (sigaddset(&ourset, SIGINT) || sigaddset(&ourset, SIGQUIT))
+          {
+            warn (_("cannot set signal handler"));
+            caught_signal = true;
+          }
+      }
+    if (!caught_signal && (sigaddset(&ourset, SIGTERM)
+                    || sigaddset(&ourset, SIGALRM)
+                    || sigaction(SIGTERM, &action, NULL)
+                    || sigprocmask(SIG_UNBLOCK, &ourset, NULL))) {
+	  warn (_("cannot set signal handler"));
+	  caught_signal = true;
+	}
+    if (!caught_signal && !same_session && (sigaction(SIGINT, &action, NULL)
+                                     || sigaction(SIGQUIT, &action, NULL)))
+      {
+        warn (_("cannot set signal handler"));
+        caught_signal = true;
+      }
+    }
+  if (!caught_signal)
+    {
+      pid_t pid;
+      for (;;)
+	{
+	  pid = waitpid (child, &status, WUNTRACED);
+
+	  if (pid != (pid_t)-1 && WIFSTOPPED (status))
+	    {
+	      kill (getpid (), SIGSTOP);
+	      /* once we get here, we must have resumed */
+	      kill (pid, SIGCONT);
+	    }
+	  else
+	    break;
+	}
+      if (pid != (pid_t)-1)
+	if (WIFSIGNALED (status))
+	  status = WTERMSIG (status) + 128;
+	else
+	  status = WEXITSTATUS (status);
+      else
+	status = 1;
+    }
+  else
+    status = 1;
+
+  if (caught_signal)
+    {
+      fprintf (stderr, _("\nSession terminated, killing shell..."));
+      kill (child, SIGTERM);
+    }
+
+  cleanup_pam (PAM_SUCCESS);
+
+  if (caught_signal)
+    {
+      sleep (2);
+      kill (child, SIGKILL);
+      fprintf (stderr, _(" ...killed.\n"));
+    }
+  exit (status);
+}
+
+static void
+authenticate (const struct passwd *pw)
+{
+  const struct passwd *lpw;
+  const char *cp;
+  int retval;
+
+  retval = pam_start (simulate_login ? PAM_SERVICE_NAME_L : PAM_SERVICE_NAME,
+		      pw->pw_name, &conv, &pamh);
+  if (is_pam_failure(retval))
+    goto done;
+
+  if (isatty (0) && (cp = ttyname (0)) != NULL)
+    {
+      const char *tty;
+
+      if (strncmp (cp, "/dev/", 5) == 0)
+	tty = cp + 5;
+      else
+	tty = cp;
+      retval = pam_set_item (pamh, PAM_TTY, tty);
+      if (is_pam_failure(retval))
+	goto done;
+    }
+
+  lpw = getpwuid (getuid ());
+  if (lpw && lpw->pw_name)
+    {
+      retval = pam_set_item (pamh, PAM_RUSER, (const void *) lpw->pw_name);
+      if (is_pam_failure(retval))
+	goto done;
+    }
+
+  retval = pam_authenticate (pamh, 0);
+  if (is_pam_failure(retval))
+    goto done;
+
+  retval = pam_acct_mgmt (pamh, 0);
+  if (retval == PAM_NEW_AUTHTOK_REQD)
+    {
+      /* Password has expired.  Offer option to change it.  */
+      retval = pam_chauthtok (pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
+    }
+
+done:
+
+  log_su (pw, !is_pam_failure(retval));
+
+  if (is_pam_failure(retval))
+    {
+      const char *msg = pam_strerror(pamh, retval);
+      pam_end(pamh, retval);
+      sleep (getlogindefs_num ("FAIL_DELAY", 1));
+      errx (EXIT_FAILURE, "%s", msg?msg:_("incorrect password"));
+    }
+}
+
+/* Add or clear /sbin and /usr/sbin for the su command
+   used without `-'.  */
+
+/* Set if /sbin is found in path.  */
+#define SBIN_MASK	0x01
+/* Set if /usr/sbin is found in path.  */
+#define USBIN_MASK	0x02
+
+static char *
+addsbin (const char *const path)
+{
+  unsigned char smask = 0;
+  char *ptr, *tmp, *cur, *ret = NULL;
+  size_t len;
+
+  if (!path || *path == 0)
+    return NULL;
+
+  tmp = xstrdup (path);
+  cur = tmp;
+  for (ptr = strsep (&cur, ":"); ptr != NULL; ptr = strsep (&cur, ":"))
+    {
+      if (!strcmp (ptr, "/sbin"))
+	smask |= SBIN_MASK;
+      if (!strcmp (ptr, "/usr/sbin"))
+	smask |= USBIN_MASK;
+    }
+
+  if ((smask & (USBIN_MASK|SBIN_MASK)) == (USBIN_MASK|SBIN_MASK))
+    {
+      free (tmp);
+      return NULL;
+    }
+
+  len = strlen (path);
+  if (!(smask & USBIN_MASK))
+    len += strlen ("/usr/sbin:");
+
+  if (!(smask & SBIN_MASK))
+    len += strlen (":/sbin");
+
+  ret = xmalloc (len + 1);
+  strcpy (tmp, path);
+
+  *ret = 0;
+  cur = tmp;
+  for (ptr = strsep (&cur, ":"); ptr; ptr = strsep (&cur, ":"))
+    {
+      if (!strcmp (ptr, "."))
+	continue;
+      if (*ret)
+	strcat (ret, ":");
+      if (!(smask & USBIN_MASK) && !strcmp (ptr, "/bin"))
+	{
+	  strcat (ret, "/usr/sbin:");
+	  strcat (ret, ptr);
+	  smask |= USBIN_MASK;
+	  continue;
+	}
+      if (!(smask & SBIN_MASK) && !strcmp (ptr, "/usr/bin"))
+	{
+	  strcat (ret, ptr);
+	  strcat (ret, ":/sbin");
+	  smask |= SBIN_MASK;
+	  continue;
+	}
+      strcat (ret, ptr);
+    }
+  free (tmp);
+
+  if (!(smask & USBIN_MASK))
+    strcat (ret, ":/usr/sbin");
+
+  if (!(smask & SBIN_MASK))
+    strcat (ret, ":/sbin");
+
+  return ret;
+}
+
+static char *
+clearsbin (const char *const path)
+{
+  char *ptr, *tmp, *cur, *ret = NULL;
+
+  if (!path || *path == 0)
+    return NULL;
+
+  tmp = xstrdup (path);
+
+  ret = xmalloc (strlen (path) + 1);
+  *ret = 0;
+  cur = tmp;
+  for (ptr = strsep (&cur, ":"); ptr; ptr = strsep (&cur, ":"))
+    {
+      if (!strcmp (ptr, "/sbin"))
+	continue;
+      if (!strcmp (ptr, "/usr/sbin"))
+	continue;
+      if (!strcmp (ptr, "/usr/local/sbin"))
+	continue;
+      if (*ret)
+	strcat (ret, ":");
+      strcat (ret, ptr);
+    }
+  free (tmp);
+
+  return ret;
+}
+
+static void
+set_path(const struct passwd* pw)
+{
+  int r;
+  if (pw->pw_uid)
+    r = logindefs_setenv("PATH", "ENV_PATH", _PATH_DEFPATH);
+
+  else if ((r = logindefs_setenv("PATH", "ENV_ROOTPATH", NULL)) != 0)
+    r = logindefs_setenv("PATH", "ENV_SUPATH", _PATH_DEFPATH_ROOT);
+
+  if (r != 0)
+    err (EXIT_FAILURE,  _("failed to set PATH"));
+}
+
+/* Update `environ' for the new shell based on PW, with SHELL being
+   the value for the SHELL environment variable.  */
+
+static void
+modify_environment (const struct passwd *pw, const char *shell)
+{
+  if (simulate_login)
+    {
+      /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
+         Unset all other environment variables.  */
+      char const *term = getenv ("TERM");
+      if (term)
+	term = xstrdup (term);
+      environ = xmalloc ((6 + !!term) * sizeof (char *));
+      environ[0] = NULL;
+      if (term)
+	xsetenv ("TERM", term, 1);
+      xsetenv ("HOME", pw->pw_dir, 1);
+      xsetenv ("SHELL", shell, 1);
+      xsetenv ("USER", pw->pw_name, 1);
+      xsetenv ("LOGNAME", pw->pw_name, 1);
+      set_path(pw);
+    }
+  else
+    {
+      /* Set HOME, SHELL, and if not becoming a super-user,
+	 USER and LOGNAME.  */
+      if (change_environment)
+        {
+          xsetenv ("HOME", pw->pw_dir, 1);
+          xsetenv ("SHELL", shell, 1);
+	  if (getlogindefs_bool ("ALWAYS_SET_PATH", 0))
+	    set_path(pw);
+	  else
+	    {
+	      char const *path = getenv ("PATH");
+	      char *new = NULL;
+
+	      if (pw->pw_uid)
+		new = clearsbin (path);
+	      else
+		new = addsbin (path);
+
+	      if (new)
+		{
+		  xsetenv ("PATH", new, 1);
+		  free (new);
+		}
+	    }
+          if (pw->pw_uid)
+            {
+              xsetenv ("USER", pw->pw_name, 1);
+              xsetenv ("LOGNAME", pw->pw_name, 1);
+            }
+        }
+    }
+
+  export_pamenv ();
+}
+
+/* Become the user and group(s) specified by PW.  */
+
+static void
+init_groups (const struct passwd *pw, gid_t *groups, int num_groups)
+{
+  int retval;
+
+  errno = 0;
+
+  if (num_groups)
+    retval = setgroups (num_groups, groups);
+  else
+    retval = initgroups (pw->pw_name, pw->pw_gid);
+
+  if (retval == -1)
+    {
+      cleanup_pam (PAM_ABORT);
+      err (EXIT_FAILURE, _("cannot set groups"));
+    }
+  endgrent ();
+
+  retval = pam_setcred (pamh, PAM_ESTABLISH_CRED);
+  if (is_pam_failure(retval))
+    errx (EXIT_FAILURE, "%s", pam_strerror (pamh, retval));
+  else
+    _pam_cred_established = 1;
+}
+
+static void
+change_identity (const struct passwd *pw)
+{
+  if (setgid (pw->pw_gid))
+    err (EXIT_FAILURE,  _("cannot set group id"));
+  if (setuid (pw->pw_uid))
+    err (EXIT_FAILURE,  _("cannot set user id"));
+}
+
+/* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
+   If COMMAND is nonzero, pass it to the shell with the -c option.
+   Pass ADDITIONAL_ARGS to the shell as more arguments; there
+   are N_ADDITIONAL_ARGS extra arguments.  */
+
+static void
+run_shell (char const *shell, char const *command, char **additional_args,
+	   size_t n_additional_args)
+{
+  size_t n_args = 1 + fast_startup + 2 * !!command + n_additional_args + 1;
+  char const **args = xcalloc (n_args, sizeof *args);
+  size_t argno = 1;
+
+  if (simulate_login)
+    {
+      char *arg0;
+      char *shell_basename;
+
+      shell_basename = basename (shell);
+      arg0 = xmalloc (strlen (shell_basename) + 2);
+      arg0[0] = '-';
+      strcpy (arg0 + 1, shell_basename);
+      args[0] = arg0;
+    }
+  else
+    args[0] = basename (shell);
+  if (fast_startup)
+    args[argno++] = "-f";
+  if (command)
+    {
+      args[argno++] = "-c";
+      args[argno++] = command;
+    }
+  memcpy (args + argno, additional_args, n_additional_args * sizeof *args);
+  args[argno + n_additional_args] = NULL;
+  execv (shell, (char **) args);
+
+  {
+    int exit_status = (errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE);
+    warn ("%s", shell);
+    exit (exit_status);
+  }
+}
+
+/* Return true if SHELL is a restricted shell (one not returned by
+   getusershell), else false, meaning it is a standard shell.  */
+
+static bool
+restricted_shell (const char *shell)
+{
+  char *line;
+
+  setusershell ();
+  while ((line = getusershell ()) != NULL)
+    {
+      if (*line != '#' && !strcmp (line, shell))
+	{
+	  endusershell ();
+	  return false;
+	}
+    }
+  endusershell ();
+  return true;
+}
+
+static void __attribute__((__noreturn__))
+usage (int status)
+{
+  if (status != EXIT_SUCCESS)
+    fprintf (stderr, _("Try `%s --help' for more information.\n"),
+	     program_invocation_short_name);
+  else
+    {
+      fputs(USAGE_HEADER, stdout);
+      printf (_(" %s [options] [-] [USER [arg]...]\n"), program_invocation_short_name);
+      fputs (_("\n\
+ Change the effective user id and group id to that of USER.\n\
+ A mere - implies -l.   If USER not given, assume root.\n"), stdout);
+      fputs(USAGE_OPTIONS, stdout);
+      fputs (_("\
+ -, -l, --login               make the shell a login shell\n\
+ -c, --command <command>      pass a single command to the shell with -c\n\
+ --session-command <command>  pass a single command to the shell with -c\n\
+                              and do not create a new session\n\
+ -g --group=group             specify the primary group\n\
+ -G --supp-group=group        specify a supplemental group\n\
+ -f, --fast                   pass -f to the shell (for csh or tcsh)\n\
+ -m, --preserve-environment   do not reset environment variables\n\
+ -p                           same as -m\n\
+ -s, --shell <shell>          run shell if /etc/shells allows it\n\
+"), stdout);
+
+      fputs(USAGE_SEPARATOR, stdout);
+      fputs(USAGE_HELP, stdout);
+      fputs(USAGE_VERSION, stdout);
+      printf(USAGE_MAN_TAIL("su(1)"));
+    }
+  exit (status);
+}
+
+static
+void load_config(void)
+{
+  logindefs_load_file("/etc/default/su");
+  logindefs_load_file(_PATH_LOGINDEFS);
+}
+
+/*
+ * Returns 1 if the current user is not root
+ */
+static int
+evaluate_uid(void)
+{
+  uid_t ruid = getuid();
+  uid_t euid = geteuid();
+
+  /* if we're really root and aren't running setuid */
+  return (uid_t) 0 == ruid && ruid == euid ? 0 : 1;
+}
+
+int
+su_main (int argc, char **argv, int mode)
+{
+  int optc;
+  const char *new_user = DEFAULT_USER;
+  char *command = NULL;
+  int request_same_session = 0;
+  char *shell = NULL;
+  struct passwd *pw;
+  struct passwd pw_copy;
+  struct group *gr;
+  gid_t groups[NGROUPS_MAX];
+  int num_supp_groups = 0;
+  int use_gid = 0;
+  int restricted;
+
+  setlocale (LC_ALL, "");
+  bindtextdomain (PACKAGE, LOCALEDIR);
+  textdomain (PACKAGE);
+
+  su_mode = mode;
+  fast_startup = false;
+  simulate_login = false;
+  change_environment = true;
+
+  while ((optc = getopt_long (argc, argv, "c:fg:G:lmps:hV", longopts, NULL)) != -1)
+    {
+      switch (optc)
+	{
+	case 'c':
+	  command = optarg;
+	  break;
+
+        case 'C':
+          command = optarg;
+          request_same_session = 1;
+          break;
+
+	case 'f':
+	  fast_startup = true;
+	  break;
+
+	case 'g':
+	  gr = getgrnam(optarg);
+	  if (!gr)
+	    errx(EXIT_FAILURE, _("group %s does not exist"), optarg);
+	  use_gid = 1;
+	  groups[0] = gr->gr_gid;
+	  break;
+
+	case 'G':
+	  num_supp_groups++;
+	  if (num_supp_groups >= NGROUPS_MAX)
+	     errx(EXIT_FAILURE,
+		  _("can't specify more than %d supplemental groups"),
+		  NGROUPS_MAX - 1);
+	  gr = getgrnam(optarg);
+	  if (!gr)
+	    errx(EXIT_FAILURE, _("group %s does not exist"), optarg);
+	  groups[num_supp_groups] = gr->gr_gid;
+	  break;
+
+	case 'l':
+	  simulate_login = true;
+	  break;
+
+	case 'm':
+	case 'p':
+	  change_environment = false;
+	  break;
+
+	case 's':
+	  shell = optarg;
+	  break;
+
+	case 'h':
+	  usage(0);
+
+	case 'V':
+	  printf(UTIL_LINUX_VERSION);
+	  exit(EXIT_SUCCESS);
+
+	default:
+	  usage (EXIT_FAILURE);
+	}
+    }
+
+  restricted = evaluate_uid ();
+
+  if (optind < argc && !strcmp (argv[optind], "-"))
+    {
+      simulate_login = true;
+      ++optind;
+    }
+  if (optind < argc)
+    new_user = argv[optind++];
+
+  if ((num_supp_groups || use_gid) && restricted)
+    errx(EXIT_FAILURE, _("only root can specify alternative groups"));
+
+  logindefs_load_defaults = load_config;
+
+  pw = getpwnam (new_user);
+  if (! (pw && pw->pw_name && pw->pw_name[0] && pw->pw_dir && pw->pw_dir[0]
+	 && pw->pw_passwd))
+    errx (EXIT_FAILURE, _("user %s does not exist"), new_user);
+
+  /* Make a copy of the password information and point pw at the local
+     copy instead.  Otherwise, some systems (e.g. Linux) would clobber
+     the static data through the getlogin call from log_su.
+     Also, make sure pw->pw_shell is a nonempty string.
+     It may be NULL when NEW_USER is a username that is retrieved via NIS (YP),
+     but that doesn't have a default shell listed.  */
+  pw_copy = *pw;
+  pw = &pw_copy;
+  pw->pw_name = xstrdup (pw->pw_name);
+  pw->pw_passwd = xstrdup (pw->pw_passwd);
+  pw->pw_dir = xstrdup (pw->pw_dir);
+  pw->pw_shell = xstrdup (pw->pw_shell && pw->pw_shell[0]
+			  ? pw->pw_shell
+			  : DEFAULT_SHELL);
+  endpwent ();
+
+  if (num_supp_groups && !use_gid)
+  {
+    pw->pw_gid = groups[1];
+    memmove (groups, groups + 1, sizeof(gid_t) * num_supp_groups);
+  }
+  else if (use_gid)
+  {
+    pw->pw_gid = groups[0];
+    num_supp_groups++;
+  }
+
+  authenticate (pw);
+
+  if (request_same_session || !command || !pw->pw_uid)
+    same_session = 1;
+
+  if (!shell && !change_environment)
+    shell = getenv ("SHELL");
+  if (shell && getuid () != 0 && restricted_shell (pw->pw_shell))
+    {
+      /* The user being su'd to has a nonstandard shell, and so is
+	 probably a uucp account or has restricted access.  Don't
+	 compromise the account by allowing access with a standard
+	 shell.  */
+      warnx (_("using restricted shell %s"), pw->pw_shell);
+      shell = NULL;
+    }
+  shell = xstrdup (shell ? shell : pw->pw_shell);
+
+  init_groups (pw, groups, num_supp_groups);
+
+  create_watching_parent ();
+  /* Now we're in the child.  */
+
+  change_identity (pw);
+  if (!same_session)
+    setsid ();
+
+  /* Set environment after pam_open_session, which may put KRB5CCNAME
+     into the pam_env, etc.  */
+
+  modify_environment (pw, shell);
+
+  if (simulate_login && chdir (pw->pw_dir) != 0)
+    warn (_("warning: cannot change directory to %s"), pw->pw_dir);
+
+  run_shell (shell, command, argv + optind, max (0, argc - optind));
+}
+
+// vim: sw=2 cinoptions=>4,n-2,{2,^-2,\:2,=2,g0,h2,p5,t0,+2,(0,u0,w1,m1