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