/* 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 . */ enum { EXIT_CANNOT_INVOKE = 126, EXIT_ENOENT = 127 }; #include #include #include #include #include #include #include #include #include #include #include #include "err.h" #include #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 pass a single command to the shell with -c\n\ --session-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 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