libc/stdlib/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    see <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <grp.h>
  22 #include <limits.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/resource.h>
  26 #include <sys/stat.h>
  27 #include <sys/types.h>
  28 #include <sys/wait.h>
  29 #include <unistd.h>
  30 #include "pty-private.h"
  31
  32
  33 /* Return the result of ptsname_r in the buffer pointed to by PTS,
  34    which should be of length BUF_LEN.  If it is too long to fit in
  35    this buffer, a sufficiently long buffer is allocated using malloc,
  36    and returned in PTS.  0 is returned upon success, -1 otherwise.  */
  37 static int
  38 pts_name (int fd, char **pts, size_t buf_len)
  39 {
  40   int rv;
  41   char *buf = *pts;
  42
  43   for (;;)
  44     {
  45       char *new_buf;
  46
  47       if (buf_len)
  48         {
  49           rv = ptsname_r (fd, buf, buf_len);
  50
  51           if (rv != 0 || memchr (buf, '\0', buf_len))
  52             /* We either got an error, or we succeeded and the
  53                returned name fit in the buffer.  */
  54             break;
  55
  56           /* Try again with a longer buffer.  */
  57           buf_len += buf_len;   /* Double it */
  58         }
  59       else
  60         /* No initial buffer; start out by mallocing one.  */
  61         buf_len = 128;          /* First time guess.  */
  62
  63       if (buf != *pts)
  64         /* We've already malloced another buffer at least once.  */
  65         new_buf = realloc (buf, buf_len);
  66       else
  67         new_buf = malloc (buf_len);
  68       if (! new_buf)
  69         {
  70           rv = -1;
  71           /* __set_errno(ENOMEM); */
  72           break;
  73         }
  74       buf = new_buf;
  75     }
  76
  77   if (rv == 0)
  78     *pts = buf;         /* Return buffer to the user.  */
  79   else if (buf != *pts)
  80     free (buf);         /* Free what we malloced when returning an error.  */
  81
  82   return rv;
  83 }
  84
  85 /* Change the ownership and access permission of the slave pseudo
  86    terminal associated with the master pseudo terminal specified
  87    by FD.  */
  88 int
  89 grantpt (int fd)
  90 {
  91   int retval = -1;
  92 #ifdef PATH_MAX
  93   char _buf[PATH_MAX];
  94 #else
  95   char _buf[512];
  96 #endif
  97   char *buf = _buf;
  98   struct stat st;
  99   uid_t uid;
 100   gid_t gid;
 101   pid_t pid;
 102
 103   if (pts_name (fd, &buf, sizeof (_buf)))
 104     return -1;
 105
 106   if (stat(buf, &st) < 0)
 107     goto cleanup;
 108
 109   /* Make sure that we own the device.  */
 110   uid = getuid ();
 111   if (st.st_uid != uid)
 112     {
 113       if (chown (buf, uid, st.st_gid) < 0)
 114         goto helper;
 115     }
 116
 117   gid = getgid ();
 118
 119   /* Make sure the group of the device is that special group.  */
 120   if (st.st_gid != gid)
 121     {
 122       if (chown (buf, uid, gid) < 0)
 123         goto helper;
 124     }
 125
 126   /* Make sure the permission mode is set to readable and writable by
 127      the owner, and writable by the group.  */
 128   if ((st.st_mode & ACCESSPERMS) != (S_IRUSR|S_IWUSR|S_IWGRP))
 129     {
 130       if (chmod (buf, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
 131         goto helper;
 132     }
 133
 134   retval = 0;
 135   goto cleanup;
 136
 137   /* We have to use the helper program.  */
 138  helper:
 139
 140   pid = vfork ();
 141   if (pid == -1)
 142     goto cleanup;
 143   else if (pid == 0)
 144     {
 145       /* Disable core dumps.  */
 146       struct rlimit rl = { 0, 0 };
 147       setrlimit (RLIMIT_CORE, &rl);
 148
 149       /* We pase the master pseudo terminal as file descriptor PTY_FILENO.  */
 150       if (fd != PTY_FILENO)
 151         if (dup2 (fd, PTY_FILENO) < 0)
 152           _exit (FAIL_EBADF);
 153
 154       execle (_PATH_PT_CHOWN, _PATH_PT_CHOWN, NULL, NULL);
 155       _exit (FAIL_EXEC);
 156     }
 157   else
 158     {
 159       int w;
 160
 161       if (waitpid (pid, &w, 0) == -1)
 162         goto cleanup;
 163       if (!WIFEXITED (w))
 164         errno = ENOEXEC;
 165       else
 166         switch (WEXITSTATUS(w))
 167           {
 168           case 0:
 169             retval = 0;
 170             break;
 171           case FAIL_EBADF:
 172             errno = EBADF;
 173             break;
 174           case FAIL_EINVAL:
 175             errno = EINVAL;
 176             break;
 177           case FAIL_EACCES:
 178             errno = EACCES;
 179             break;
 180           case FAIL_EXEC:
 181             errno = ENOEXEC;
 182             break;
 183
 184           default:
 185             assert(! "getpt: internal error: invalid exit code from pt_chown");
 186           }
 187     }
 188
 189  cleanup:
 190   if (buf != _buf)
 191     free (buf);
 192
 193   return retval;
 194 }