]> git.ipfire.org Git - thirdparty/util-linux.git/blobdiff - login-utils/su-common.c
mkswap: be more explicit about maximal number of pages
[thirdparty/util-linux.git] / login-utils / su-common.c
index 265f5fd624d9168fab5e30e05e5e9ca01d641e0d..1662d21bbac3cf82fa7432e85b715d6cd303e5a5 100644 (file)
@@ -3,7 +3,7 @@
  *
  * Copyright (C) 1992-2006 Free Software Foundation, Inc.
  * Copyright (C) 2012 SUSE Linux Products GmbH, Nuernberg
- * Copyright (C) 2016 Karel Zak <kzak@redhat.com>
+ * Copyright (C) 2016-2017 Karel Zak <kzak@redhat.com>
  *
  * 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
 #include <syslog.h>
 #include <utmpx.h>
 
+#if defined(HAVE_LIBUTIL) && defined(HAVE_PTY_H) && defined(HAVE_SYS_SIGNALFD_H)
+# include <pty.h>
+# include <poll.h>
+# include <sys/signalfd.h>
+# include "all-io.h"
+# define USE_PTY
+#endif
+
 #include "err.h"
 
 #include <stdbool.h>
 #include "pathnames.h"
 #include "env.h"
 #include "closestream.h"
+#include "strv.h"
 #include "strutils.h"
 #include "ttyutils.h"
 #include "pwdutils.h"
+#include "optutils.h"
 
 #include "logindefs.h"
 #include "su-common.h"
@@ -66,6 +76,7 @@ UL_DEBUG_DEFINE_MASKNAMES(su) = UL_DEBUG_EMPTY_MASKNAMES;
 #define SU_DEBUG_LOG           (1 << 5)
 #define SU_DEBUG_MISC          (1 << 6)
 #define SU_DEBUG_SIG           (1 << 7)
+#define SU_DEBUG_PTY           (1 << 8)
 #define SU_DEBUG_ALL           0xFFFF
 
 #define DBG(m, x)       __UL_DBG(su, SU_DEBUG_, m, x)
@@ -94,11 +105,6 @@ UL_DEBUG_DEFINE_MASKNAMES(su) = UL_DEBUG_EMPTY_MASKNAMES;
 extern char **environ;
 #endif
 
-enum {
-       EXIT_CANNOT_INVOKE = 126,
-       EXIT_ENOENT = 127
-};
-
 enum {
        SIGTERM_IDX = 0,
        SIGINT_IDX,
@@ -121,12 +127,25 @@ struct su_context {
        const char      *tty_number;            /* end of the tty_path */
 
        char            *new_user;              /* wanted user */
-       char            *old_user;              /* orginal user */
+       char            *old_user;              /* original user */
 
        pid_t           child;                  /* fork() baby */
+       int             childstatus;            /* wait() status */
+
+       char            **env_whitelist_names;  /* environment whitelist */
+       char            **env_whitelist_vals;
 
        struct sigaction oldact[SIGNALS_IDX_COUNT];     /* original sigactions indexed by SIG*_IDX */
 
+#ifdef USE_PTY
+       struct termios  stdin_attrs;            /* stdin and slave terminal runtime attributes */
+       int             pty_master;
+       int             pty_slave;
+       int             pty_sigfd;              /* signalfd() */
+       int             poll_timeout;
+       struct winsize  win;                    /* terminal window size */
+       sigset_t        oldsig;                 /* original signal mask */
+#endif
        unsigned int runuser :1,                /* flase=su, true=runuser */
                     runuser_uopt :1,           /* runuser -u specified */
                     isterm :1,                 /* is stdin terminal? */
@@ -153,17 +172,418 @@ su_catch_sig(int sig)
 
 static void su_init_debug(void)
 {
-       __UL_INIT_DEBUG(su, SU_DEBUG_, 0, SU_DEBUG);
+       __UL_INIT_DEBUG_FROM_ENV(su, SU_DEBUG_, 0, SU_DEBUG);
 }
 
 static void init_tty(struct su_context *su)
 {
        su->isterm = isatty(STDIN_FILENO) ? 1 : 0;
-       DBG(TTY, ul_debug("initilize [is-term=%s]", su->isterm ? "true" : "false"));
+       DBG(TTY, ul_debug("initialize [is-term=%s]", su->isterm ? "true" : "false"));
        if (su->isterm)
                get_terminal_name(NULL, &su->tty_name, &su->tty_number);
 }
 
+/*
+ * Note, this function has to be possible call more than once. If the child is
+ * already dead than it returns saved result from the previous call.
+ */
+static int wait_for_child(struct su_context *su)
+{
+       pid_t pid = (pid_t) -1;;
+       int status = 0;
+
+       if (su->child == (pid_t) -1)
+               return su->childstatus;
+
+       if (su->child != (pid_t) -1) {
+               /*
+                * The "su" parent process spends all time here in waitpid(),
+                * but "su --pty" uses pty_proxy_master() and waitpid() is only
+                * called to pick up child status or to react to SIGSTOP.
+                */
+               DBG(SIG, ul_debug("waiting for child [%d]...", su->child));
+               for (;;) {
+                       pid = waitpid(su->child, &status, WUNTRACED);
+
+                       if (pid != (pid_t) - 1 && WIFSTOPPED(status)) {
+                               DBG(SIG, ul_debug(" child got SIGSTOP -- stop all session"));
+                               kill(getpid(), SIGSTOP);
+                               /* once we get here, we must have resumed */
+                               kill(pid, SIGCONT);
+                               DBG(SIG, ul_debug(" session resumed -- continue"));
+#ifdef USE_PTY
+                               /* Let's go back to pty_proxy_master() */
+                               if (su->pty_sigfd != -1) {
+                                       DBG(SIG, ul_debug(" leaving on child SIGSTOP"));
+                                       return 0;
+                               }
+#endif
+                       } else
+                               break;
+               }
+       }
+       if (pid != (pid_t) -1) {
+               if (WIFSIGNALED(status)) {
+                       fprintf(stderr, "%s%s\n",
+                               strsignal(WTERMSIG(status)),
+                               WCOREDUMP(status) ? _(" (core dumped)")
+                               : "");
+                       status = WTERMSIG(status) + 128;
+               } else
+                       status = WEXITSTATUS(status);
+
+               DBG(SIG, ul_debug("child %d is dead", su->child));
+               su->child = (pid_t) -1; /* Don't use the PID anymore! */
+               su->childstatus = status;
+       } else if (caught_signal)
+               status = caught_signal + 128;
+       else
+               status = 1;
+
+       DBG(SIG, ul_debug("child status=%d", status));
+       return status;
+}
+
+
+#ifdef USE_PTY
+static void pty_init_slave(struct su_context *su)
+{
+       DBG(PTY, ul_debug("initialize slave"));
+
+       ioctl(su->pty_slave, TIOCSCTTY, 1);
+       close(su->pty_master);
+
+       dup2(su->pty_slave, STDIN_FILENO);
+       dup2(su->pty_slave, STDOUT_FILENO);
+       dup2(su->pty_slave, STDERR_FILENO);
+
+       close(su->pty_slave);
+       close(su->pty_sigfd);
+
+       su->pty_slave = -1;
+       su->pty_master = -1;
+       su->pty_sigfd = -1;
+
+       sigprocmask(SIG_SETMASK, &su->oldsig, NULL);
+
+       DBG(PTY, ul_debug("... initialize slave done"));
+}
+
+static void pty_create(struct su_context *su)
+{
+       struct termios slave_attrs;
+       int rc;
+
+       if (su->isterm) {
+               DBG(PTY, ul_debug("create for terminal"));
+
+               /* original setting of the current terminal */
+               if (tcgetattr(STDIN_FILENO, &su->stdin_attrs) != 0)
+                       err(EXIT_FAILURE, _("failed to get terminal attributes"));
+               ioctl(STDIN_FILENO, TIOCGWINSZ, (char *)&su->win);
+               /* create master+slave */
+               rc = openpty(&su->pty_master, &su->pty_slave, NULL, &su->stdin_attrs, &su->win);
+
+               /* set the current terminal to raw mode; pty_cleanup() reverses this change on exit */
+               slave_attrs = su->stdin_attrs;
+               cfmakeraw(&slave_attrs);
+               slave_attrs.c_lflag &= ~ECHO;
+               tcsetattr(STDIN_FILENO, TCSANOW, &slave_attrs);
+       } else {
+               DBG(PTY, ul_debug("create for non-terminal"));
+               rc = openpty(&su->pty_master, &su->pty_slave, NULL, NULL, NULL);
+
+               if (!rc) {
+                       tcgetattr(su->pty_slave, &slave_attrs);
+                       slave_attrs.c_lflag &= ~ECHO;
+                       tcsetattr(su->pty_slave, TCSANOW, &slave_attrs);
+               }
+       }
+
+       if (rc < 0)
+               err(EXIT_FAILURE, _("failed to create pseudo-terminal"));
+
+       DBG(PTY, ul_debug("pty setup done [master=%d, slave=%d]", su->pty_master, su->pty_slave));
+}
+
+static void pty_cleanup(struct su_context *su)
+{
+       struct termios rtt;
+
+       if (su->pty_master == -1 || !su->isterm)
+               return;
+
+       DBG(PTY, ul_debug("cleanup"));
+       rtt = su->stdin_attrs;
+       tcsetattr(STDIN_FILENO, TCSADRAIN, &rtt);
+}
+
+static int write_output(char *obuf, ssize_t bytes)
+{
+       DBG(PTY, ul_debug(" writing output"));
+
+       if (write_all(STDOUT_FILENO, obuf, bytes)) {
+               DBG(PTY, ul_debug("  writing output *failed*"));
+               warn(_("write failed"));
+               return -errno;
+       }
+
+       return 0;
+}
+
+static int write_to_child(struct su_context *su,
+                         char *buf, size_t bufsz)
+{
+       return write_all(su->pty_master, buf, bufsz);
+}
+
+/*
+ * The su(1) is usually faster than shell, so it's a good idea to wait until
+ * the previous message has been already read by shell from slave before we
+ * write to master. This is necessary especially for EOF situation when we can
+ * send EOF to master before shell is fully initialized, to workaround this
+ * problem we wait until slave is empty. For example:
+ *
+ *   echo "date" | su
+ *
+ * Unfortunately, the child (usually shell) can ignore stdin at all, so we
+ * don't wait forever to avoid dead locks...
+ *
+ * Note that su --pty is primarily designed for interactive sessions as it
+ * maintains master+slave tty stuff within the session. Use pipe to write to
+ * su(1) and assume non-interactive (tee-like) behavior is NOT well
+ * supported.
+ */
+static void write_eof_to_child(struct su_context *su)
+{
+       unsigned int tries = 0;
+       struct pollfd fds[] = {
+                  { .fd = su->pty_slave, .events = POLLIN }
+       };
+       char c = DEF_EOF;
+
+       DBG(PTY, ul_debug(" waiting for empty slave"));
+       while (poll(fds, 1, 10) == 1 && tries < 8) {
+               DBG(PTY, ul_debug("   slave is not empty"));
+               xusleep(250000);
+               tries++;
+       }
+       if (tries < 8)
+               DBG(PTY, ul_debug("   slave is empty now"));
+
+       DBG(PTY, ul_debug(" sending EOF to master"));
+       write_to_child(su, &c, sizeof(char));
+}
+
+static int pty_handle_io(struct su_context *su, int fd, int *eof)
+{
+       char buf[BUFSIZ];
+       ssize_t bytes;
+
+       DBG(PTY, ul_debug("%d FD active", fd));
+       *eof = 0;
+
+       /* read from active FD */
+       bytes = read(fd, buf, sizeof(buf));
+       if (bytes < 0) {
+               if (errno == EAGAIN || errno == EINTR)
+                       return 0;
+               return -errno;
+       }
+
+       if (bytes == 0) {
+               *eof = 1;
+               return 0;
+       }
+
+       /* from stdin (user) to command */
+       if (fd == STDIN_FILENO) {
+               DBG(PTY, ul_debug(" stdin --> master %zd bytes", bytes));
+
+               if (write_to_child(su, buf, bytes)) {
+                       warn(_("write failed"));
+                       return -errno;
+               }
+               /* without sync write_output() will write both input &
+                * shell output that looks like double echoing */
+               fdatasync(su->pty_master);
+
+       /* from command (master) to stdout */
+       } else if (fd == su->pty_master) {
+               DBG(PTY, ul_debug(" master --> stdout %zd bytes", bytes));
+               write_output(buf, bytes);
+       }
+
+       return 0;
+}
+
+static int pty_handle_signal(struct su_context *su, int fd)
+{
+       struct signalfd_siginfo info;
+       ssize_t bytes;
+
+       DBG(SIG, ul_debug("signal FD %d active", fd));
+
+       bytes = read(fd, &info, sizeof(info));
+       if (bytes != sizeof(info)) {
+               if (bytes < 0 && (errno == EAGAIN || errno == EINTR))
+                       return 0;
+               return -errno;
+       }
+
+       switch (info.ssi_signo) {
+       case SIGCHLD:
+               DBG(SIG, ul_debug(" get signal SIGCHLD"));
+
+               /* The child terminated or stopped. Note that we ignore SIGCONT
+                * here, because stop/cont semantic is handled by wait_for_child() */
+               if (info.ssi_code == CLD_EXITED
+                   || info.ssi_code == CLD_KILLED
+                   || info.ssi_code == CLD_DUMPED
+                   || info.ssi_status == SIGSTOP)
+                       wait_for_child(su);
+               /* The child is dead, force poll() timeout. */
+               if (su->child == (pid_t) -1)
+                       su->poll_timeout = 10;
+               return 0;
+       case SIGWINCH:
+               DBG(SIG, ul_debug(" get signal SIGWINCH"));
+               if (su->isterm) {
+                       ioctl(STDIN_FILENO, TIOCGWINSZ, (char *)&su->win);
+                       ioctl(su->pty_slave, TIOCSWINSZ, (char *)&su->win);
+               }
+               break;
+       case SIGTERM:
+               /* fallthrough */
+       case SIGINT:
+               /* fallthrough */
+       case SIGQUIT:
+               DBG(SIG, ul_debug(" get signal SIG{TERM,INT,QUIT}"));
+               caught_signal = info.ssi_signo;
+                /* Child termination is going to generate SIGCHILD (see above) */
+                kill(su->child, SIGTERM);
+               break;
+       default:
+               abort();
+       }
+
+       return 0;
+}
+
+static void pty_proxy_master(struct su_context *su)
+{
+       sigset_t ourset;
+       int rc = 0, ret, eof = 0;
+       enum {
+               POLLFD_SIGNAL = 0,
+               POLLFD_MASTER,
+               POLLFD_STDIN
+
+       };
+       struct pollfd pfd[] = {
+               [POLLFD_SIGNAL] = { .fd = -1,             .events = POLLIN | POLLERR | POLLHUP },
+               [POLLFD_MASTER] = { .fd = su->pty_master, .events = POLLIN | POLLERR | POLLHUP },
+               [POLLFD_STDIN]  = { .fd = STDIN_FILENO,   .events = POLLIN | POLLERR | POLLHUP }
+       };
+
+       /* for PTY mode we use signalfd
+        *
+        * TODO: script(1) initializes this FD before fork, good or bad idea?
+        */
+       sigfillset(&ourset);
+       if (sigprocmask(SIG_BLOCK, &ourset, NULL)) {
+               warn(_("cannot block signals"));
+               caught_signal = true;
+               return;
+       }
+
+       sigemptyset(&ourset);
+       sigaddset(&ourset, SIGCHLD);
+       sigaddset(&ourset, SIGWINCH);
+       sigaddset(&ourset, SIGALRM);
+       sigaddset(&ourset, SIGTERM);
+       sigaddset(&ourset, SIGINT);
+       sigaddset(&ourset, SIGQUIT);
+
+       if ((su->pty_sigfd = signalfd(-1, &ourset, SFD_CLOEXEC)) < 0) {
+               warn(("cannot create signal file descriptor"));
+               caught_signal = true;
+               return;
+       }
+
+       pfd[POLLFD_SIGNAL].fd = su->pty_sigfd;
+       su->poll_timeout = -1;
+
+       while (!caught_signal) {
+               size_t i;
+               int errsv;
+
+               DBG(PTY, ul_debug("calling poll()"));
+
+               /* wait for input or signal */
+               ret = poll(pfd, ARRAY_SIZE(pfd), su->poll_timeout);
+               errsv = errno;
+               DBG(PTY, ul_debug("poll() rc=%d", ret));
+
+               if (ret < 0) {
+                       if (errsv == EAGAIN)
+                               continue;
+                       warn(_("poll failed"));
+                       break;
+               }
+               if (ret == 0) {
+                       DBG(PTY, ul_debug("leaving poll() loop [timeout=%d]", su->poll_timeout));
+                       break;
+               }
+
+               for (i = 0; i < ARRAY_SIZE(pfd); i++) {
+                       rc = 0;
+
+                       if (pfd[i].revents == 0)
+                               continue;
+
+                       DBG(PTY, ul_debug(" active pfd[%s].fd=%d %s %s %s",
+                                               i == POLLFD_STDIN  ? "stdin" :
+                                               i == POLLFD_MASTER ? "master" :
+                                               i == POLLFD_SIGNAL ? "signal" : "???",
+                                               pfd[i].fd,
+                                               pfd[i].revents & POLLIN  ? "POLLIN" : "",
+                                               pfd[i].revents & POLLHUP ? "POLLHUP" : "",
+                                               pfd[i].revents & POLLERR ? "POLLERR" : ""));
+                       switch (i) {
+                       case POLLFD_STDIN:
+                       case POLLFD_MASTER:
+                               /* data */
+                               if (pfd[i].revents & POLLIN)
+                                       rc = pty_handle_io(su, pfd[i].fd, &eof);
+                               /* EOF maybe detected by two ways:
+                                *      A) poll() return POLLHUP event after close()
+                                *      B) read() returns 0 (no data) */
+                               if ((pfd[i].revents & POLLHUP) || eof) {
+                                       DBG(PTY, ul_debug(" ignore FD"));
+                                       pfd[i].fd = -1;
+                                       if (i == POLLFD_STDIN) {
+                                               write_eof_to_child(su);
+                                               DBG(PTY, ul_debug("  ignore STDIN"));
+                                       }
+                               }
+                               continue;
+                       case POLLFD_SIGNAL:
+                               rc = pty_handle_signal(su, pfd[i].fd);
+                               break;
+                       }
+                       if (rc)
+                               break;
+               }
+       }
+
+       close(su->pty_sigfd);
+       su->pty_sigfd = -1;
+       DBG(PTY, ul_debug("poll() done [signal=%d, rc=%d]", caught_signal, rc));
+}
+#endif /* USE_PTY */
+
+
 /* Log the fact that someone has run su to the user given by PW;
    if SUCCESSFUL is true, they gave the correct password, etc.  */
 
@@ -191,14 +611,14 @@ static void log_btmp(struct su_context *su)
        DBG(LOG, ul_debug("btmp logging"));
 
        memset(&ut, 0, sizeof(ut));
-       strncpy(ut.ut_user,
+       str2memcpy(ut.ut_user,
                su->pwd && su->pwd->pw_name ? su->pwd->pw_name : "(unknown)",
                sizeof(ut.ut_user));
 
        if (su->tty_number)
-               xstrncpy(ut.ut_id, su->tty_number, sizeof(ut.ut_id));
+               str2memcpy(ut.ut_id, su->tty_number, sizeof(ut.ut_id));
        if (su->tty_name)
-               xstrncpy(ut.ut_line, su->tty_name, sizeof(ut.ut_line));
+               str2memcpy(ut.ut_line, su->tty_name, sizeof(ut.ut_line));
 
        gettimeofday(&tv, NULL);
        ut.ut_tv.tv_sec = tv.tv_sec;
@@ -333,45 +753,6 @@ static void supam_open_session(struct su_context *su)
                su->pam_has_session = 1;
 }
 
-static int wait_for_child(struct su_context *su)
-{
-       pid_t pid = (pid_t) -1;;
-       int status = 0;
-
-       if (su->child != (pid_t) -1) {
-               DBG(SIG, ul_debug("waiting for child [%d]...", su->child));
-               for (;;) {
-                       pid = waitpid(su->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)) {
-                       fprintf(stderr, "%s%s\n",
-                               strsignal(WTERMSIG(status)),
-                               WCOREDUMP(status) ? _(" (core dumped)")
-                               : "");
-                       status = WTERMSIG(status) + 128;
-               } else
-                       status = WEXITSTATUS(status);
-
-               DBG(SIG, ul_debug("child %d is dead", su->child));
-               su->child = (pid_t) -1; /* Don't use the PID anymore! */
-       } else if (caught_signal)
-               status = caught_signal + 128;
-       else
-               status = 1;
-
-       DBG(SIG, ul_debug("status=%d", status));
-       return status;
-}
-
 static void parent_setup_signals(struct su_context *su)
 {
        sigset_t ourset;
@@ -448,10 +829,22 @@ static void create_watching_parent(struct su_context *su)
        int status;
 
        DBG(MISC, ul_debug("forking..."));
+#ifdef USE_PTY
+       /* no-op, just save original signal mask to oldsig */
+       sigprocmask(SIG_BLOCK, NULL, &su->oldsig);
+
+       if (su->pty)
+               pty_create(su);
+#endif
+       fflush(stdout);                 /* ??? */
 
        switch ((int) (su->child = fork())) {
        case -1: /* error */
                supam_cleanup(su, PAM_ABORT);
+#ifdef USE_PTY
+               if (su->pty)
+                       pty_cleanup(su);
+#endif
                err(EXIT_FAILURE, _("cannot create child process"));
                break;
 
@@ -463,6 +856,8 @@ static void create_watching_parent(struct su_context *su)
                break;
        }
 
+       /* free unnecessary stuff */
+       free_getlogindefs_data();
 
        /* In the parent watch the child.  */
 
@@ -470,8 +865,12 @@ static void create_watching_parent(struct su_context *su)
           sitting on any directory so let's go to /.  */
        if (chdir("/") != 0)
                warn(_("cannot change directory to %s"), "/");
-
-       parent_setup_signals(su);
+#ifdef USE_PTY
+       if (su->pty)
+               pty_proxy_master(su);
+       else
+#endif
+               parent_setup_signals(su);
 
        /*
         * Wait for child
@@ -481,6 +880,8 @@ static void create_watching_parent(struct su_context *su)
        else
                status = 1;
 
+       DBG(SIG, ul_debug("final child status=%d", status));
+
        if (caught_signal && su->child != (pid_t)-1) {
                fprintf(stderr, _("\nSession terminated, killing shell..."));
                kill(su->child, SIGTERM);
@@ -523,10 +924,64 @@ static void create_watching_parent(struct su_context *su)
                kill(getpid(), caught_signal);
        }
 
+#ifdef USE_PTY
+       if (su->pty)
+               pty_cleanup(su);
+#endif
        DBG(MISC, ul_debug("exiting [rc=%d]", status));
        exit(status);
 }
 
+/* Adds @name from the current environment to the whitelist. If @name is not
+ * set then nothing is added to the whitelist and returns 1.
+ */
+static int env_whitelist_add(struct su_context *su, const char *name)
+{
+       const char *env = getenv(name);
+
+       if (!env)
+               return 1;
+       if (strv_extend(&su->env_whitelist_names, name))
+                err_oom();
+       if (strv_extend(&su->env_whitelist_vals, env))
+                err_oom();
+       return 0;
+}
+
+static int env_whitelist_setenv(struct su_context *su, int overwrite)
+{
+       char **one;
+       size_t i = 0;
+       int rc;
+
+       STRV_FOREACH(one, su->env_whitelist_names) {
+               rc = setenv(*one, su->env_whitelist_vals[i], overwrite);
+               if (rc)
+                       return rc;
+               i++;
+       }
+
+       return 0;
+}
+
+/* Creates (add to) whitelist from comma delimited string */
+static int env_whitelist_from_string(struct su_context *su, const char *str)
+{
+       char **all = strv_split(str, ",");
+       char **one;
+
+       if (!all) {
+               if (errno == ENOMEM)
+                       err_oom();
+               return -EINVAL;
+       }
+
+       STRV_FOREACH(one, all)
+               env_whitelist_add(su, *one);
+       strv_free(all);
+       return 0;
+}
+
 static void setenv_path(const struct passwd *pw)
 {
        int rc;
@@ -536,8 +991,8 @@ static void setenv_path(const struct passwd *pw)
        if (pw->pw_uid)
                rc = logindefs_setenv("PATH", "ENV_PATH", _PATH_DEFPATH);
 
-       else if ((rc = logindefs_setenv("PATH", "ENV_ROOTPATH", NULL)) != 0)
-               rc = logindefs_setenv("PATH", "ENV_SUPATH", _PATH_DEFPATH_ROOT);
+       else if ((rc = logindefs_setenv("PATH", "ENV_SUPATH", NULL)) != 0)
+               rc = logindefs_setenv("PATH", "ENV_ROOTPATH", _PATH_DEFPATH_ROOT);
 
        if (rc)
                err(EXIT_FAILURE, _("failed to set the PATH environment variable"));
@@ -551,26 +1006,38 @@ static void modify_environment(struct su_context *su, const char *shell)
        DBG(MISC, ul_debug("modify environ[]"));
 
        /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
-        * Unset all other environment variables.
+        *
+        * Unset all other environment variables, but follow
+        * --whitelist-environment if specified.
         */
        if (su->simulate_login) {
-               char *term = getenv("TERM");
-               if (term)
-                       term = xstrdup(term);
-
-               environ = xmalloc((6 + ! !term) * sizeof(char *));
-               environ[0] = NULL;
-               if (term) {
-                       xsetenv("TERM", term, 1);
-                       free(term);
-               }
-
-               xsetenv("HOME", pw->pw_dir, 1);
+               /* leave TERM unchanged */
+               env_whitelist_add(su, "TERM");
+
+               /* Note that original su(1) has allocated environ[] by malloc
+                * to the number of expected variables. This seems unnecessary
+                * optimization as libc later realloc(current_size+2) and for
+                * empty environ[] the curren_size is zero. It seems better to
+                * keep all logic around environment in glibc's hands.
+                *                                           --kzak [Aug 2018]
+                */
+#ifdef HAVE_CLEARENV
+               clearenv();
+#else
+               environ = NULL;
+#endif
+               /* always reset */
                if (shell)
                        xsetenv("SHELL", shell, 1);
+
+               setenv_path(pw);
+
+               xsetenv("HOME", pw->pw_dir, 1);
                xsetenv("USER", pw->pw_name, 1);
                xsetenv("LOGNAME", pw->pw_name, 1);
-               setenv_path(pw);
+
+               /* apply all from whitelist, but no overwrite */
+               env_whitelist_setenv(su, 0);
 
        /* Set HOME, SHELL, and (if not becoming a superuser) USER and LOGNAME.
         */
@@ -638,7 +1105,6 @@ static void run_shell(
        size_t n_args = 1 + su->fast_startup + 2 * ! !command + n_additional_args + 1;
        const char **args = xcalloc(n_args, sizeof *args);
        size_t argno = 1;
-       int rc;
 
        DBG(MISC, ul_debug("starting shell [shell=%s, command=\"%s\"%s%s]",
                                shell, command,
@@ -667,9 +1133,7 @@ static void run_shell(
        memcpy(args + argno, additional_args, n_additional_args * sizeof *args);
        args[argno + n_additional_args] = NULL;
        execv(shell, (char **)args);
-
-       rc = errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE;
-       err(rc, _("failed to execute %s"), shell);
+       errexec(shell);
 }
 
 /* Return true if SHELL is a restricted shell (one not returned by
@@ -694,7 +1158,10 @@ static bool is_restricted_shell(const char *shell)
 
 static void usage_common(void)
 {
-       fputs(_(" -m, -p, --preserve-environment  do not reset environment variables\n"), stdout);
+       fputs(_(" -m, -p, --preserve-environment      do not reset environment variables\n"), stdout);
+       fputs(_(" -w, --whitelist-environment <list>  don't reset specified variables\n"), stdout);
+       fputs(USAGE_SEPARATOR, stdout);
+
        fputs(_(" -g, --group <group>             specify the primary group\n"), stdout);
        fputs(_(" -G, --supp-group <group>        specify a supplemental group\n"), stdout);
        fputs(USAGE_SEPARATOR, stdout);
@@ -705,7 +1172,7 @@ static void usage_common(void)
                "                                   and do not create a new session\n"), stdout);
        fputs(_(" -f, --fast                      pass -f to the shell (for csh or tcsh)\n"), stdout);
        fputs(_(" -s, --shell <shell>             run <shell> if /etc/shells allows it\n"), stdout);
-       fputs(_(" -P, --pty                       create pseudo-terminal session\n"), stdout);
+       fputs(_(" -P, --pty                       create a new pseudo-terminal\n"), stdout);
 
        fputs(USAGE_SEPARATOR, stdout);
        printf(USAGE_HELP_OPTIONS(33));
@@ -764,8 +1231,8 @@ static void load_config(void *data)
        struct su_context *su = (struct su_context *) data;
 
        DBG(MISC, ul_debug("loading logindefs"));
-       logindefs_load_file(su->runuser ? _PATH_LOGINDEFS_RUNUSER : _PATH_LOGINDEFS_SU);
        logindefs_load_file(_PATH_LOGINDEFS);
+       logindefs_load_file(su->runuser ? _PATH_LOGINDEFS_RUNUSER : _PATH_LOGINDEFS_SU);
 }
 
 /*
@@ -809,7 +1276,12 @@ int su_main(int argc, char **argv, int mode)
                .conv                   = { supam_conv, NULL },
                .runuser                = (mode == RUNUSER_MODE ? 1 : 0),
                .change_environment     = 1,
-               .new_user               = DEFAULT_USER
+               .new_user               = DEFAULT_USER,
+#ifdef USE_PTY
+               .pty_master             = -1,
+               .pty_slave              = -1,
+               .pty_sigfd              = -1,
+#endif
        }, *su = &_su;
 
        int optc;
@@ -834,10 +1306,17 @@ int su_main(int argc, char **argv, int mode)
                {"group", required_argument, NULL, 'g'},
                {"supp-group", required_argument, NULL, 'G'},
                {"user", required_argument, NULL, 'u'}, /* runuser only */
+               {"whitelist-environment", required_argument, NULL, 'w'},
                {"help", no_argument, 0, 'h'},
                {"version", no_argument, 0, 'V'},
                {NULL, 0, NULL, 0}
        };
+       static const ul_excl_t excl[] = {       /* rows and cols in ASCII order */
+               { 'm', 'w' },                   /* preserve-environment, whitelist-environment */
+               { 'p', 'w' },                   /* preserve-environment, whitelist-environment */
+               { 0 }
+       };
+       int excl_st[ARRAY_SIZE(excl)] = UL_EXCL_STATUS_INIT;
 
        setlocale(LC_ALL, "");
        bindtextdomain(PACKAGE, LOCALEDIR);
@@ -848,8 +1327,11 @@ int su_main(int argc, char **argv, int mode)
        su->conv.appdata_ptr = (void *) su;
 
        while ((optc =
-               getopt_long(argc, argv, "c:fg:G:lmpPs:u:hV", longopts,
+               getopt_long(argc, argv, "c:fg:G:lmpPs:u:hVw:", longopts,
                            NULL)) != -1) {
+
+               err_exclusive_options(optc, longopts, excl, excl_st);
+
                switch (optc) {
                case 'c':
                        command = optarg;
@@ -883,8 +1365,16 @@ int su_main(int argc, char **argv, int mode)
                        su->change_environment = false;
                        break;
 
+               case 'w':
+                       env_whitelist_from_string(su, optarg);
+                       break;
+
                case 'P':
+#ifdef USE_PTY
                        su->pty = 1;
+#else
+                       errx(EXIT_FAILURE, _("--pty is not supported for your system"));
+#endif
                        break;
 
                case 's':
@@ -1008,9 +1498,14 @@ int su_main(int argc, char **argv, int mode)
        /* Now we're in the child.  */
 
        change_identity(su->pwd);
-       if (!su->same_session)
+       if (!su->same_session || su->pty) {
+               DBG(MISC, ul_debug("call setsid()"));
                setsid();
-
+       }
+#ifdef USE_PTY
+       if (su->pty)
+               pty_init_slave(su);
+#endif
        /* Set environment after pam_open_session, which may put KRB5CCNAME
           into the pam_env, etc.  */