sysdeps/unix/grantpt.c

   1 /* Copyright (C) 1998, 2000, 2001, 2002 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    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           if (rv != 0)
  53             {
  54               if (rv == ENOTTY)
  55                 /* ptsname_r returns with ENOTTY to indicate
  56                    a descriptor not referring to a pty master.
  57                    For this condition, grantpt must return EINVAL.  */
  58                 rv = EINVAL;
  59               errno = rv;       /* Not necessarily set by __ptsname_r.  */
  60               break;
  61             }
  62
  63           if (memchr (buf, '\0', buf_len))
  64             /* We succeeded and the returned name fit in the buffer.  */
  65             break;
  66
  67           /* Try again with a longer buffer.  */
  68           buf_len += buf_len;   /* Double it */
  69         }
  70       else
  71         /* No initial buffer; start out by mallocing one.  */
  72         buf_len = 128;          /* First time guess.  */
  73
  74       if (buf != *pts)
  75         /* We've already malloced another buffer at least once.  */
  76         new_buf = (char *) realloc (buf, buf_len);
  77       else
  78         new_buf = (char *) malloc (buf_len);
  79       if (! new_buf)
  80         {
  81           rv = -1;
  82           __set_errno (ENOMEM);
  83           break;
  84         }
  85       buf = new_buf;
  86     }
  87
  88   if (rv == 0)
  89     *pts = buf;         /* Return buffer to the user.  */
  90   else if (buf != *pts)
  91     free (buf);         /* Free what we malloced when returning an error.  */
  92
  93   return rv;
  94 }
  95
  96 /* Change the ownership and access permission of the slave pseudo
  97    terminal associated with the master pseudo terminal specified
  98    by FD.  */
  99 int
 100 grantpt (int fd)
 101 {
 102   int retval = -1;
 103 #ifdef PATH_MAX
 104   char _buf[PATH_MAX];
 105 #else
 106   char _buf[512];
 107 #endif
 108   char *buf = _buf;
 109   struct stat64 st;
 110   char *grtmpbuf;
 111   struct group grbuf;
 112   size_t grbuflen = __sysconf (_SC_GETGR_R_SIZE_MAX);
 113   struct group *p;
 114   uid_t uid;
 115   gid_t gid;
 116   pid_t pid;
 117
 118   if (pts_name (fd, &buf, sizeof (_buf)))
 119     return -1;
 120
 121   if (__xstat64 (_STAT_VER, buf, &st) < 0)
 122     goto cleanup;
 123
 124   /* Make sure that we own the device.  */
 125   uid = __getuid ();
 126   if (st.st_uid != uid)
 127     {
 128       if (__chown (buf, uid, st.st_gid) < 0)
 129         goto helper;
 130     }
 131
 132   /* Get the group ID of the special `tty' group.  */
 133   if (grbuflen == (size_t) -1L)
 134     /* `sysconf' does not support _SC_GETGR_R_SIZE_MAX.
 135        Try a moderate value.  */
 136     grbuflen = 1024;
 137   grtmpbuf = (char *) __alloca (grbuflen);
 138   __getgrnam_r (TTY_GROUP, &grbuf, grtmpbuf, grbuflen, &p);
 139   gid = p ? p->gr_gid : __getgid ();
 140
 141   /* Make sure the group of the device is that special group.  */
 142   if (st.st_gid != gid)
 143     {
 144       if (__chown (buf, uid, gid) < 0)
 145         goto helper;
 146     }
 147
 148   /* Make sure the permission mode is set to readable and writable by
 149      the owner, and writable by the group.  */
 150   if ((st.st_mode & ACCESSPERMS) != (S_IRUSR|S_IWUSR|S_IWGRP))
 151     {
 152       if (__chmod (buf, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
 153         goto helper;
 154     }
 155
 156   retval = 0;
 157   goto cleanup;
 158
 159   /* We have to use the helper program.  */
 160  helper:
 161
 162   pid = __fork ();
 163   if (pid == -1)
 164     goto cleanup;
 165   else if (pid == 0)
 166     {
 167       /* Disable core dumps.  */
 168       struct rlimit rl = { 0, 0 };
 169       __setrlimit (RLIMIT_CORE, &rl);
 170
 171       /* We pass the master pseudo terminal as file descriptor PTY_FILENO.  */
 172       if (fd != PTY_FILENO)
 173         if (__dup2 (fd, PTY_FILENO) < 0)
 174           _exit (FAIL_EBADF);
 175
 176       execle (_PATH_PT_CHOWN, basename (_PATH_PT_CHOWN), NULL, NULL);
 177       _exit (FAIL_EXEC);
 178     }
 179   else
 180     {
 181       int w;
 182
 183       if (__waitpid (pid, &w, 0) == -1)
 184         goto cleanup;
 185       if (!WIFEXITED (w))
 186         __set_errno (ENOEXEC);
 187       else
 188         switch (WEXITSTATUS(w))
 189           {
 190           case 0:
 191             retval = 0;
 192             break;
 193           case FAIL_EBADF:
 194             __set_errno (EBADF);
 195             break;
 196           case FAIL_EINVAL:
 197             __set_errno (EINVAL);
 198             break;
 199           case FAIL_EACCES:
 200             __set_errno (EACCES);
 201             break;
 202           case FAIL_EXEC:
 203             __set_errno (ENOEXEC);
 204             break;
 205
 206           default:
 207             assert(! "getpt: internal error: invalid exit code from pt_chown");
 208           }
 209     }
 210
 211  cleanup:
 212   if (buf != _buf)
 213     free (buf);
 214
 215   return retval;
 216 }