From cf1a99dacc9b1b6a091e03906b60c47774a339f5 Mon Sep 17 00:00:00 2001 From: Karel Zak Date: Tue, 28 Aug 2012 18:10:58 +0200 Subject: su: move generic su code to su-common.c Signed-off-by: Karel Zak --- login-utils/su-common.c | 883 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 883 insertions(+) create mode 100644 login-utils/su-common.c (limited to 'login-utils/su-common.c') 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 . */ + +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 -- cgit v1.2.3-55-g7522