sshpty.c

/*
 * Dropbear - a SSH2 server
 *
 * Copied from OpenSSH-3.5p1 source, modified by Matt Johnston 2003
 * 
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Allocating a pseudo-terminal, and making it the controlling tty.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

/*RCSID("OpenBSD: sshpty.c,v 1.7 2002/06/24 17:57:20 deraadt Exp ");*/

#include "includes.h"
#include "dbutil.h"
#include "errno.h"
#include "sshpty.h"

/* Pty allocated with _getpty gets broken if we do I_PUSH:es to it. */
#if defined(HAVE__GETPTY) || defined(HAVE_OPENPTY)
#undef HAVE_DEV_PTMX
#endif

#ifdef HAVE_PTY_H
# include <pty.h>
#endif
#if defined(USE_DEV_PTMX) && defined(HAVE_STROPTS_H)
# include <stropts.h>
#endif

#ifndef O_NOCTTY
#define O_NOCTTY 0
#endif

/*
 * Allocates and opens a pty.  Returns 0 if no pty could be allocated, or
 * nonzero if a pty was successfully allocated.  On success, open file
 * descriptors for the pty and tty sides and the name of the tty side are
 * returned (the buffer must be able to hold at least 64 characters).
 */

int
pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, int namebuflen)
{
#if defined(HAVE_OPENPTY)
      /* exists in recent (4.4) BSDs and OSF/1 */
      char *name;
      int i;

      i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
      if (i < 0) {
            dropbear_log(LOG_WARNING, 
                        "pty_allocate: openpty: %.100s", strerror(errno));
            return 0;
      }
      name = ttyname(*ttyfd);
      if (!name) {
            dropbear_exit("ttyname fails for openpty device");
      }

      strlcpy(namebuf, name, namebuflen); /* possible truncation */
      return 1;
#else /* HAVE_OPENPTY */
#ifdef HAVE__GETPTY
      /*
       * _getpty(3) exists in SGI Irix 4.x, 5.x & 6.x -- it generates more
       * pty's automagically when needed
       */
      char *slave;

      slave = _getpty(ptyfd, O_RDWR, 0622, 0);
      if (slave == NULL) {
            dropbear_log(LOG_WARNING,
                        "pty_allocate: _getpty: %.100s", strerror(errno));
            return 0;
      }
      strlcpy(namebuf, slave, namebuflen);
      /* Open the slave side. */
      *ttyfd = open(namebuf, O_RDWR | O_NOCTTY);
      if (*ttyfd < 0) {
            dropbear_log(LOG_WARNING,
                        "pty_allocate error: ttyftd open error");
            close(*ptyfd);
            return 0;
      }
      return 1;
#else /* HAVE__GETPTY */
#if defined(USE_DEV_PTMX)
      /*
       * This code is used e.g. on Solaris 2.x.  (Note that Solaris 2.3
       * also has bsd-style ptys, but they simply do not work.)
       *
       * Linux systems may have the /dev/ptmx device, but this code won't work.
       */
      int ptm;
      char *pts;

      ptm = open("/dev/ptmx", O_RDWR | O_NOCTTY);
      if (ptm < 0) {
            dropbear_log(LOG_WARNING,
                        "pty_allocate: /dev/ptmx: %.100s", strerror(errno));
            return 0;
      }
      if (grantpt(ptm) < 0) {
            dropbear_log(LOG_WARNING,
                        "grantpt: %.100s", strerror(errno));
            return 0;
      }
      if (unlockpt(ptm) < 0) {
            dropbear_log(LOG_WARNING,
                        "unlockpt: %.100s", strerror(errno));
            return 0;
      }
      pts = ptsname(ptm);
      if (pts == NULL) {
            dropbear_log(LOG_WARNING,
                        "Slave pty side name could not be obtained.");
      }
      strlcpy(namebuf, pts, namebuflen);
      *ptyfd = ptm;

      /* Open the slave side. */
      *ttyfd = open(namebuf, O_RDWR | O_NOCTTY);
      if (*ttyfd < 0) {
            dropbear_log(LOG_ERR,
                  "error opening pts %.100s: %.100s", namebuf, strerror(errno));
            close(*ptyfd);
            return 0;
      }
#ifndef HAVE_CYGWIN
      /*
       * Push the appropriate streams modules, as described in Solaris pts(7).
       * HP-UX pts(7) doesn't have ttcompat module.
       */
      if (ioctl(*ttyfd, I_PUSH, "ptem") < 0) {
            dropbear_log(LOG_WARNING,
                        "ioctl I_PUSH ptem: %.100s", strerror(errno));
      }
      if (ioctl(*ttyfd, I_PUSH, "ldterm") < 0) {
            dropbear_log(LOG_WARNING,
                  "ioctl I_PUSH ldterm: %.100s", strerror(errno));
      }
#ifndef __hpux
      if (ioctl(*ttyfd, I_PUSH, "ttcompat") < 0) {
            dropbear_log(LOG_WARNING,
                  "ioctl I_PUSH ttcompat: %.100s", strerror(errno));
      }
#endif
#endif
      return 1;
#else /* USE_DEV_PTMX */
#ifdef HAVE_DEV_PTS_AND_PTC
      /* AIX-style pty code. */
      const char *name;

      *ptyfd = open("/dev/ptc", O_RDWR | O_NOCTTY);
      if (*ptyfd < 0) {
            dropbear_log(LOG_ERR,
                  "Could not open /dev/ptc: %.100s", strerror(errno));
            return 0;
      }
      name = ttyname(*ptyfd);
      if (!name) {
            dropbear_exit("ttyname fails for /dev/ptc device");
      }
      strlcpy(namebuf, name, namebuflen);
      *ttyfd = open(name, O_RDWR | O_NOCTTY);
      if (*ttyfd < 0) {
            dropbear_log(LOG_ERR,
                  "Could not open pty slave side %.100s: %.100s",
                name, strerror(errno));
            close(*ptyfd);
            return 0;
      }
      return 1;
#else /* HAVE_DEV_PTS_AND_PTC */

      /* BSD-style pty code. */
      char buf[64];
      int i;
      const char *ptymajors = "pqrstuvwxyzabcdefghijklmnoABCDEFGHIJKLMNOPQRSTUVWXYZ";
      const char *ptyminors = "0123456789abcdef";
      int num_minors = strlen(ptyminors);
      int num_ptys = strlen(ptymajors) * num_minors;
      struct termios tio;

      for (i = 0; i < num_ptys; i++) {
            snprintf(buf, sizeof buf, "/dev/pty%c%c", ptymajors[i / num_minors],
                   ptyminors[i % num_minors]);
            snprintf(namebuf, namebuflen, "/dev/tty%c%c",
                ptymajors[i / num_minors], ptyminors[i % num_minors]);

            *ptyfd = open(buf, O_RDWR | O_NOCTTY);
            if (*ptyfd < 0) {
                  /* Try SCO style naming */
                  snprintf(buf, sizeof buf, "/dev/ptyp%d", i);
                  snprintf(namebuf, namebuflen, "/dev/ttyp%d", i);
                  *ptyfd = open(buf, O_RDWR | O_NOCTTY);
                  if (*ptyfd < 0) {
                        continue;
                  }
            }

            /* Open the slave side. */
            *ttyfd = open(namebuf, O_RDWR | O_NOCTTY);
            if (*ttyfd < 0) {
                  dropbear_log(LOG_ERR,
                        "pty_allocate: %.100s: %.100s", namebuf, strerror(errno));
                  close(*ptyfd);
                  return 0;
            }
            /* set tty modes to a sane state for broken clients */
            if (tcgetattr(*ptyfd, &tio) < 0) {
                  dropbear_log(LOG_WARNING,
                        "ptyallocate: tty modes failed: %.100s", strerror(errno));
            } else {
                  tio.c_lflag |= (ECHO | ISIG | ICANON);
                  tio.c_oflag |= (OPOST | ONLCR);
                  tio.c_iflag |= ICRNL;

                  /* Set the new modes for the terminal. */
                  if (tcsetattr(*ptyfd, TCSANOW, &tio) < 0) {
                        dropbear_log(LOG_WARNING,
                              "Setting tty modes for pty failed: %.100s",
                              strerror(errno));
                  }
            }

            return 1;
      }
      dropbear_log(LOG_WARNING, "failed to open any /dev/pty?? devices");
      return 0;
#endif /* HAVE_DEV_PTS_AND_PTC */
#endif /* USE_DEV_PTMX */
#endif /* HAVE__GETPTY */
#endif /* HAVE_OPENPTY */
}

/* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */

void
pty_release(const char *tty_name)
{
      if (chown(tty_name, (uid_t) 0, (gid_t) 0) < 0
                  && (errno != ENOENT)) {
            dropbear_log(LOG_ERR,
                        "chown %.100s 0 0 failed: %.100s", tty_name, strerror(errno));
      }
      if (chmod(tty_name, (mode_t) 0666) < 0
                  && (errno != ENOENT)) {
            dropbear_log(LOG_ERR,
                  "chmod %.100s 0666 failed: %.100s", tty_name, strerror(errno));
      }
}

/* Makes the tty the processes controlling tty and sets it to sane modes. */

void
pty_make_controlling_tty(int *ttyfd, const char *tty_name)
{
      int fd;
#ifdef USE_VHANGUP
      void *old;
#endif /* USE_VHANGUP */

      /* Solaris has a problem with TIOCNOTTY for a bg process, so
       * we disable the signal which would STOP the process - matt */
      signal(SIGTTOU, SIG_IGN);

      /* First disconnect from the old controlling tty. */
#ifdef TIOCNOTTY
      fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
      if (fd >= 0) {
            (void) ioctl(fd, TIOCNOTTY, NULL);
            close(fd);
      }
#endif /* TIOCNOTTY */
      if (setsid() < 0) {
            dropbear_log(LOG_ERR,
                  "setsid: %.100s", strerror(errno));
      }

      /*
       * Verify that we are successfully disconnected from the controlling
       * tty.
       */
      fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
      if (fd >= 0) {
            dropbear_log(LOG_ERR,
                        "Failed to disconnect from controlling tty.\n");
            close(fd);
      }
      /* Make it our controlling tty. */
#ifdef TIOCSCTTY
      if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0) {
            dropbear_log(LOG_ERR,
                  "ioctl(TIOCSCTTY): %.100s", strerror(errno));
      }
#endif /* TIOCSCTTY */
#ifdef HAVE_NEWS4
      if (setpgrp(0,0) < 0) {
            dropbear_log(LOG_ERR,
                  error("SETPGRP %s",strerror(errno)));
      }
#endif /* HAVE_NEWS4 */
#ifdef USE_VHANGUP
      old = mysignal(SIGHUP, SIG_IGN);
      vhangup();
      mysignal(SIGHUP, old);
#endif /* USE_VHANGUP */
      fd = open(tty_name, O_RDWR);
      if (fd < 0) {
            dropbear_log(LOG_ERR,
                  "%.100s: %.100s", tty_name, strerror(errno));
      } else {
#ifdef USE_VHANGUP
            close(*ttyfd);
            *ttyfd = fd;
#else /* USE_VHANGUP */
            close(fd);
#endif /* USE_VHANGUP */
      }
      /* Verify that we now have a controlling tty. */
      fd = open(_PATH_TTY, O_WRONLY);
      if (fd < 0) {
            dropbear_log(LOG_ERR,
                  "open /dev/tty failed - could not set controlling tty: %.100s",
                strerror(errno));
      } else {
            close(fd);
      }
}

/* Changes the window size associated with the pty. */

void
pty_change_window_size(int ptyfd, int row, int col,
      int xpixel, int ypixel)
{
      struct winsize w;

      w.ws_row = row;
      w.ws_col = col;
      w.ws_xpixel = xpixel;
      w.ws_ypixel = ypixel;
      (void) ioctl(ptyfd, TIOCSWINSZ, &w);
}

void
pty_setowner(struct passwd *pw, const char *tty_name)
{
      struct group *grp;
      gid_t gid;
      mode_t mode;
      struct stat st;

      /* Determine the group to make the owner of the tty. */
      grp = getgrnam("tty");
      if (grp) {
            gid = grp->gr_gid;
            mode = S_IRUSR | S_IWUSR | S_IWGRP;
      } else {
            gid = pw->pw_gid;
            mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
      }

      /*
       * Change owner and mode of the tty as required.
       * Warn but continue if filesystem is read-only and the uids match/
       * tty is owned by root.
       */
      if (stat(tty_name, &st)) {
            dropbear_exit("pty_setowner: stat(%.101s) failed: %.100s",
                        tty_name, strerror(errno));
      }

      if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
            if (chown(tty_name, pw->pw_uid, gid) < 0) {
                  if (errno == EROFS &&
                      (st.st_uid == pw->pw_uid || st.st_uid == 0)) {
                        dropbear_log(LOG_ERR,
                              "chown(%.100s, %u, %u) failed: %.100s",
                                    tty_name, (unsigned int)pw->pw_uid, (unsigned int)gid,
                                    strerror(errno));
                  } else {
                        dropbear_exit("chown(%.100s, %u, %u) failed: %.100s",
                            tty_name, (unsigned int)pw->pw_uid, (unsigned int)gid,
                            strerror(errno));
                  }
            }
      }

      if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
            if (chmod(tty_name, mode) < 0) {
                  if (errno == EROFS &&
                      (st.st_mode & (S_IRGRP | S_IROTH)) == 0) {
                        dropbear_log(LOG_ERR,
                              "chmod(%.100s, 0%o) failed: %.100s",
                              tty_name, mode, strerror(errno));
                  } else {
                        dropbear_exit("chmod(%.100s, 0%o) failed: %.100s",
                            tty_name, mode, strerror(errno));
                  }
            }
      }
}