su.c

Unix/Linux下转换用户ID的su程序源码

/* su for GNU.  Run a shell with substitute user and group IDs.
   Copyright (C) 92, 93, 94, 95, 1996 Free Software Foundation, Inc.

   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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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.

   This program intentionally does not support a "wheel group" that
   restricts who can su to UID 0 accounts.  RMS considers that to
   be fascist.

   Options:
   -, -l, --login       Make the subshell a login shell.
                        Unset all environment variables except
                        TERM, HOME and SHELL (set as above), and USER
                        and LOGNAME (set unconditionally as above), and
                        set PATH to a default value.
                        Change to USER's home directory.
                        Prepend "-" to the shell's name.
   -c, --commmand=COMMAND
                        Pass COMMAND to the subshell with a -c option
                        instead of starting an interactive shell.
   -f, --fast           Pass the -f option to the subshell.
   -m, -p, --preserve-environment
                        Do not change HOME, USER, LOGNAME, SHELL.
                        Run $SHELL instead of USER's shell from /etc/passwd
                        unless not the superuser and USER's shell is
                        restricted.
                        Overridden by --login and --shell.
   -s, --shell=shell    Run SHELL instead of USER's shell from /etc/passwd
                        unless not the superuser and USER's shell is
                        restricted.

   Compile-time options:
   -DSYSLOG_SUCCESS     Log successful su's (by default, to root) with syslog.
   -DSYSLOG_FAILURE     Log failed su's (by default, to root) with syslog.

   -DSYSLOG_NON_ROOT    Log all su's, not just those to root (UID 0).
   Never logs attempted su's to nonexistent accounts.

   Written by David MacKenzie <[e-mail]>.  */

#include <config.h>
#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
#include "system.h"

#if defined(HAVE_SYSLOG_H) && defined(HAVE_SYSLOG)
#include <syslog.h>
#else /* !HAVE_SYSLOG_H */
#ifdef SYSLOG_SUCCESS
#undef SYSLOG_SUCCESS
#endif
#ifdef SYSLOG_FAILURE
#undef SYSLOG_FAILURE
#endif
#ifdef SYSLOG_NON_ROOT
#undef SYSLOG_NON_ROOT
#endif
#endif /* !HAVE_SYSLOG_H */

#ifdef _POSIX_VERSION
#include <limits.h>
#else /* not _POSIX_VERSION */
struct passwd *getpwuid ();
struct group *getgrgid ();
uid_t getuid ();
#include <sys/param.h>
#endif /* not _POSIX_VERSION */

#ifndef HAVE_ENDGRENT
# define endgrent() ((void) 0)
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#endif

#ifndef HAVE_ENDPWENT
# define endpwent() ((void) 0)
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#endif

#ifdef HAVE_SHADOW_H
#include <shadow.h>
#endif

#include "error.h"

#ifdef HAVE_PATHS_H
#include <paths.h>
#endif

/* The default PATH for simulated logins to non-superuser accounts.  */
#ifdef _PATH_DEFPATH
#define DEFAULT_LOGIN_PATH _PATH_DEFPATH
#else
#define DEFAULT_LOGIN_PATH ":/usr/ucb:/bin:/usr/bin"
#endif

/* The default PATH for simulated logins to superuser accounts.  */
#ifdef _PATH_DEFPATH_ROOT
#define DEFAULT_ROOT_LOGIN_PATH _PATH_DEFPATH_ROOT
#else
#define DEFAULT_ROOT_LOGIN_PATH "/usr/ucb:/bin:/usr/bin:/etc"
#endif

/* 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"

char *crypt ();
char *getpass ();
char *getusershell ();
void endusershell ();
void setusershell ();

char *basename ();
char *xmalloc ();
char *xrealloc ();
char *xstrdup ();

extern char **environ;

/* The name this program was run with.  */
char *program_name;

/* If nonzero, display usage information and exit.  */
static int show_help;

/* If nonzero, print the version on standard output and exit.  */
static int show_version;

/* If nonzero, pass the `-f' option to the subshell.  */
static int fast_startup;

/* If nonzero, simulate a login instead of just starting a shell.  */
static int simulate_login;

/* If nonzero, change some environment vars to indicate the user su'd to.  */
static int change_environment;

static struct option const longopts[] =
{
  {"command", required_argument, 0, 'c'},
  {"fast", no_argument, &fast_startup, 1},
  {"help", no_argument, &show_help, 1},
  {"login", no_argument, &simulate_login, 1},
  {"preserve-environment", no_argument, &change_environment, 0},
  {"shell", required_argument, 0, 's'},
  {"version", no_argument, &show_version, 1},
  {0, 0, 0, 0}
};

/* Add VAL to the environment, checking for out of memory errors.  */

static void
xputenv (const char *val)
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{
  if (putenv (val))
    error (1, 0, _("virtual memory exhausted"));
}

/* Return a newly-allocated string whose contents concatenate
   those of S1, S2, S3.  */

static char *
concat (const char *s1, const char *s2, const char *s3)
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{
  int len1 = strlen (s1), len2 = strlen (s2), len3 = strlen (s3);
  char *result = (char *) xmalloc (len1 + len2 + len3 + 1);

  strcpy (result, s1);
  strcpy (result + len1, s2);
  strcpy (result + len1 + len2, s3);
  result[len1 + len2 + len3] = 0;

  return result;
}

/* Return the number of elements in ARR, a null-terminated array.  */

static int
elements (char **arr)
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{
  int n = 0;

  for (n = 0; *arr; ++arr)
    ++n;
  return n;
}

#if defined (SYSLOG_SUCCESS) || defined (SYSLOG_FAILURE)
/* Log the fact that someone has run su to the user given by PW;
   if SUCCESSFUL is nonzero, they gave the correct password, etc.  */

static void
log_su (const struct passwd *pw, int successful)
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{
  const char *new_user, *old_user, *tty;

#ifndef SYSLOG_NON_ROOT
  if (pw->pw_uid)
    return;
#endif
  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 == NULL)
    old_user = "";
  tty = ttyname (2);
  if (tty == NULL)
    tty = "";
  /* 4.2BSD openlog doesn't have the third parameter.  */
  openlog (basename (program_name), 0
#ifdef LOG_AUTH
           , LOG_AUTH
#endif
           );
  syslog (LOG_NOTICE,
#ifdef SYSLOG_NON_ROOT
          "%s(to %s) %s on %s",
#else
          "%s%s on %s",
#endif
          successful ? "" : "FAILED SU ",
#ifdef SYSLOG_NON_ROOT
          new_user,
#endif
          old_user, tty);
  closelog ();
}
#endif

/* Ask the user for a password.
   Return 1 if the user gives the correct password for entry PW,
   0 if not.  Return 1 without asking for a password if run by UID 0
   or if PW has an empty password.  */

static int
correct_password (const struct passwd *pw)
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{
  char *unencrypted, *encrypted, *correct;
#ifdef HAVE_SHADOW_H
  /* Shadow passwd stuff for SVR3 and maybe other systems.  */
  struct spwd *sp = getspnam (pw->pw_name);

  endspent ();
  if (sp)
    correct = sp->sp_pwdp;
  else
#endif
  correct = pw->pw_passwd;

  if (getuid () == 0 || correct == 0 || correct[0] == '\0')
    return 1;

  unencrypted = getpass (_("Password:"));