sysdeps/unix/grantpt.c

   1 /* Copyright (C) 1998 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Zack Weinberg <zack@rabi.phys.columbia.edu>, 1998.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <grp.h>
  23 #include <limits.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <sys/resource.h>
  27 #include <sys/stat.h>
  28 #include <sys/types.h>
  29 #include <sys/wait.h>
  30 #include <unistd.h>
  31
  32 #include "pty-private.h"
  33
  34
  35 /* Return the result of ptsname_r in the buffer pointed to by PTS,
  36    which should be of length BUF_LEN.  If it is too long to fit in
  37    this buffer, a sufficiently long buffer is allocated using malloc,
  38    and returned in PTS.  0 is returned upon success, -1 otherwise.  */
  39 static int
  40 pts_name (int fd, char **pts, size_t buf_len)
  41 {
  42   int rv;
  43   char *buf = *pts;
  44
  45   for (;;)
  46     {
  47       char *new_buf;
  48
  49       if (buf_len)
  50         {
  51           rv = ptsname_r (fd, buf, buf_len);
  52
  53           if (rv != 0 || memchr (buf, '\0', buf_len))
  54             /* We either got an error, or we succeeded and the
  55                returned name fit in the buffer.  */
  56             break;
  57
  58           /* Try again with a longer buffer.  */
  59           buf_len += buf_len;   /* Double it */
  60         }
  61       else
  62         /* No initial buffer; start out by mallocing one.  */
  63         buf_len = 128;          /* First time guess.  */
  64
  65       if (buf != *pts)
  66         /* We've already malloced another buffer at least once.  */
  67         new_buf = realloc (buf, buf_len);
  68       else
  69         new_buf = malloc (buf_len);
  70       if (! new_buf)
  71         {
  72           rv = -1;
  73           __set_errno (ENOMEM);
  74           break;
  75         }
  76       buf = new_buf;
  77     }
  78
  79   if (rv == 0)
  80     *pts = buf;         /* Return buffer to the user.  */
  81   else if (buf != *pts)
  82     free (buf);         /* Free what we malloced when returning an error.  */
  83
  84   return rv;
  85 }
  86
  87 /* Change the ownership and access permission of the slave pseudo
  88    terminal associated with the master pseudo terminal specified
  89    by FD.  */
  90 int
  91 grantpt (int fd)
  92 {
  93   int retval = -1;
  94 #ifdef PATH_MAX
  95   char _buf[PATH_MAX];
  96 #else
  97   char _buf[512];
  98 #endif
  99   char *buf = _buf;
 100   struct stat st;
 101   char *grtmpbuf;
 102   struct group grbuf;
 103   size_t grbuflen = __sysconf (_SC_GETGR_R_SIZE_MAX);
 104   struct group *p;
 105   uid_t uid;
 106   gid_t gid;
 107   pid_t pid;
 108
 109   if (pts_name (fd, &buf, sizeof (_buf)))
 110     return -1;
 111
 112   if (__xstat (_STAT_VER, buf, &st) < 0)
 113     goto cleanup;
 114
 115   /* Make sure that we own the device.  */
 116   uid = __getuid ();
 117   if (st.st_uid != uid)
 118     {
 119       if (__chown (buf, uid, st.st_gid) < 0)
 120         goto helper;
 121     }
 122
 123   /* Get the group ID of the special `tty' group.  */
 124   if (grbuflen == -1)
 125     /* `sysconf' does not support _SC_GETGR_R_SIZE_MAX.
 126        Try a moderate value.  */
 127     grbuflen = 1024;
 128   grtmpbuf = (char *) __alloca (grbuflen);
 129   getgrnam_r (TTY_GROUP, &grbuf, grtmpbuf, grbuflen, &p);
 130   gid = p ? p->gr_gid : __getgid ();
 131
 132   /* Make sure the group of the device is that special group.  */
 133   if (st.st_gid != gid)
 134     {
 135       if (__chown (buf, uid, gid) < 0)
 136         goto helper;
 137     }
 138
 139   /* Make sure the permission mode is set to readable and writable by
 140      the owner, and writable by the group.  */
 141   if ((st.st_mode & ACCESSPERMS) != (S_IRUSR|S_IWUSR|S_IWGRP))
 142     {
 143       if (__chmod (buf, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
 144         goto helper;
 145     }
 146
 147   retval = 0;
 148   goto cleanup;
 149
 150   /* We have to use the helper program.  */
 151  helper:
 152
 153   pid = __fork ();
 154   if (pid == -1)
 155     goto cleanup;
 156   else if (pid == 0)
 157     {
 158       /* Disable core dumps.  */
 159       struct rlimit rl = { 0, 0 };
 160       setrlimit (RLIMIT_CORE, &rl);
 161
 162       /* We pase the master pseudo terminal as file descriptor PTY_FILENO.  */
 163       if (fd != PTY_FILENO)
 164         if (__dup2 (fd, PTY_FILENO) < 0)
 165           _exit (FAIL_EBADF);
 166
 167       execle (_PATH_PT_CHOWN, basename (_PATH_PT_CHOWN), NULL, NULL);
 168       _exit (FAIL_EXEC);
 169     }
 170   else
 171     {
 172       int w;
 173
 174       if (__waitpid (pid, &w, 0) == -1)
 175         goto cleanup;
 176       if (!WIFEXITED (w))
 177         __set_errno (ENOEXEC);
 178       else
 179         switch (WEXITSTATUS(w))
 180           {
 181           case 0:
 182             retval = 0;
 183             break;
 184           case FAIL_EBADF:
 185             __set_errno (EBADF);
 186             break;
 187           case FAIL_EINVAL:
 188             __set_errno (EINVAL);
 189             break;
 190           case FAIL_EACCES:
 191             __set_errno (EACCES);
 192             break;
 193           case FAIL_EXEC:
 194             __set_errno (ENOEXEC);
 195             break;
 196
 197           default:
 198             assert(! "getpt: internal error: invalid exit code from pt_chown");
 199           }
 200     }
 201
 202  cleanup:
 203   if (buf != _buf)
 204     free (buf);
 205
 206   return retval;
 207 }