tdelibs/tdecore/kgrantpty.c

/* kgrantpty - helper program for KPty. */

/* This program is based on the glibc2.1 pt_chmod.
 * It was pulled out from there since both Linux
 * distributors and other OSes are not able to make
 * use of the glibc for different reasons.
 *
 * THIS IS A ROOT SUID PROGRAM
 *
 * Things work as following:
 *
 * In konsole we open a master pty. This can be
 * done by at most one process. Prior to opening the
 * master pty, the slave pty cannot be opened. Then, in
 * grantpty, we fork to this program. The trick is, that
 * the parameter is passed as a file handle, which cannot
 * be faked, so that we get a secure setuid root chmod/chown
 * with this program.
 *
 * We have to chown/chmod the slave pty to prevent eavesdroping.
 *
 * Contributed by Zack Weinberg <zack@rabi.phys.columbia.edu>, 1998.
 * Copyright (c) 1999 by Lars Doelle <lars.doelle@on-line.de>.
 * GPL applies.
 */

#include <config.h>

#include <sys/types.h>
#include <errno.h>
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

#include <sys/param.h>
#if defined(__FreeBSD__) || defined(__DragonFly__)
#  define BSD_PTY_HACK
#  include <paths.h>
#  include <dirent.h>
#endif

#define TTY_GROUP "tty"

int main (int argc, char *argv[])
{
  struct stat   st;
  struct group* p;
  gid_t         gid;
  uid_t         uid;
  mode_t        mod;
  char*         tty;
  int           fd;

  /* check preconditions **************************************************/
  if (argc != 3 || (strcmp(argv[1],"--grant") && strcmp(argv[1],"--revoke")))
  {
    printf("usage: %s (--grant|--revoke) <file descriptor>\n"
           "%s is a helper for the KDE core libraries.\n"
           "It is not intended to be called from the command line.\n"
           "It needs to be installed setuid root to function.\n",
           argv[0], argv[0]);
    return 1; /* FAIL */
  }

  if (geteuid () != 0)
  {
    fprintf(stderr, "%s not installed setuid root\n", argv[0]);
    return 1; /* FAIL */
  }

  fd = atoi(argv[2]);

  /* get slave pty name from master pty file handle *********/
#ifdef HAVE_PTSNAME
  tty = ptsname(fd);
  if (!tty)
#endif
  {
    /* Check that fd is a valid master pseudo terminal.  */
    char *pty = ttyname(fd);

#ifdef BSD_PTY_HACK
    if (pty == NULL)
    {
    /*
      Hack to make kgrantpty work on some versions of FreeBSD (and possibly
      other systems): ttyname(3) does not work with a file descriptor opened
      on a /dev/pty?? device.

      Instead, this code looks through all the devices in /dev for a device
      which has the same inode as our PTY_FILENO descriptor... if found, we
      have the name for our pty.
    */

      struct dirent *dirp;
      DIR *dp;
      struct stat dsb;

      if (fstat(fd, &dsb) != -1) {
        if ((dp = opendir(_PATH_DEV)) != NULL) {
          while ((dirp = readdir(dp))) {
            if (dirp->d_fileno != dsb.st_ino)
              continue;
            pty = malloc(sizeof(_PATH_DEV) + strlen(dirp->d_name));
            if (pty) {
              strcpy(pty, _PATH_DEV);
              strcat(pty, dirp->d_name);
            }
            break;
          }

          (void) closedir(dp);
        }
      }
    }
#endif

    if (pty == NULL)
    {
      fprintf(stderr,"%s: cannot determine pty name.\n",argv[0]);
      return 1; /* FAIL */
    }

    /* matches /dev/pty?? */
    if (memcmp(pty,"/dev/pty",8))
    {
      fprintf(stderr,"%s: determined a strange pty name `%s'.\n",argv[0],pty);
      return 1; /* FAIL */
    }

    tty = malloc(strlen(pty) + 1);
    strcpy(tty,"/dev/tty");
    strcat(tty,pty+8);
  }

  /* Check that the returned slave pseudo terminal is a character device.  */
  if (stat(tty, &st) < 0 || !S_ISCHR(st.st_mode))
  {
    fprintf(stderr,"%s: found `%s' not to be a character device.\n",argv[0],tty);
    return 1; /* FAIL */
  }

  /* setup parameters for the operation ***********************************/

  if (!strcmp(argv[1],"--grant"))
  {
    uid = getuid();
    p = getgrnam(TTY_GROUP);
    if (!p)
      p = getgrnam("wheel");
    gid = p ? p->gr_gid : getgid ();
    mod = S_IRUSR | S_IWUSR | S_IWGRP;
  }
  else
  {
    uid = 0;
    gid = st.st_gid == getgid () ? 0 : -1;
    mod = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
  }

  /* Perform the actual chown/chmod ************************************/

  if (chown(tty, uid, gid) < 0)
  {
    fprintf(stderr,"%s: cannot chown %s: %s\n",argv[0],tty,strerror(errno));
    return 1; /* FAIL */
  }

  if (chmod(tty, mod) < 0)
  {
    fprintf(stderr,"%s: cannot chmod %s: %s\n",argv[0],tty,strerror(errno));
    return 1; /* FAIL */
  }

  return 0; /* OK */
}