sysdeps/unix/grantpt.c

   1 /* Copyright (C) 1998-2022 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <fcntl.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
  31 #include "pty-private.h"
  32
  33
  34 /* Return the result of ptsname_r in the buffer pointed to by PTS,
  35    which should be of length BUF_LEN.  If it is too long to fit in
  36    this buffer, a sufficiently long buffer is allocated using malloc,
  37    and returned in PTS.  0 is returned upon success, -1 otherwise.  */
  38 static int
  39 pts_name (int fd, char **pts, size_t buf_len, struct stat64 *stp)
  40 {
  41   int rv;
  42   char *buf = *pts;
  43
  44   for (;;)
  45     {
  46       char *new_buf;
  47
  48       if (buf_len)
  49         {
  50           rv = __ptsname_internal (fd, buf, buf_len, stp);
  51           if (rv != 0)
  52             {
  53               if (rv == ENOTTY)
  54                 /* ptsname_r returns with ENOTTY to indicate
  55                    a descriptor not referring to a pty master.
  56                    For this condition, grantpt must return EINVAL.  */
  57                 rv = EINVAL;
  58               errno = rv;       /* Not necessarily set by __ptsname_r.  */
  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
 110   if (__glibc_unlikely (pts_name (fd, &buf, sizeof (_buf), &st)))
 111     {
 112       int save_errno = errno;
 113
 114       /* Check, if the file descriptor is valid.  pts_name returns the
 115          wrong errno number, so we cannot use that.  */
 116       if (__libc_fcntl (fd, F_GETFD) == -1 && errno == EBADF)
 117         return -1;
 118
 119        /* If the filedescriptor is no TTY, grantpt has to set errno
 120           to EINVAL.  */
 121        if (save_errno == ENOTTY)
 122          __set_errno (EINVAL);
 123        else
 124          __set_errno (save_errno);
 125
 126        return -1;
 127     }
 128
 129   /* Make sure that we own the device.  */
 130   uid_t uid = __getuid ();
 131   if (st.st_uid != uid)
 132     {
 133       if (__chown (buf, uid, st.st_gid) < 0)
 134         goto helper;
 135     }
 136
 137   static int tty_gid = -1;
 138   if (__glibc_unlikely (tty_gid == -1))
 139     {
 140       char *grtmpbuf;
 141       struct group grbuf;
 142       size_t grbuflen = __sysconf (_SC_GETGR_R_SIZE_MAX);
 143       struct group *p;
 144
 145       /* Get the group ID of the special `tty' group.  */
 146       if (grbuflen == (size_t) -1L)
 147         /* `sysconf' does not support _SC_GETGR_R_SIZE_MAX.
 148            Try a moderate value.  */
 149         grbuflen = 1024;
 150       grtmpbuf = (char *) __alloca (grbuflen);
 151       __getgrnam_r (TTY_GROUP, &grbuf, grtmpbuf, grbuflen, &p);
 152       if (p != NULL)
 153         tty_gid = p->gr_gid;
 154     }
 155   gid_t gid = tty_gid == -1 ? __getgid () : tty_gid;
 156
 157 #if HAVE_PT_CHOWN
 158   /* Make sure the group of the device is that special group.  */
 159   if (st.st_gid != gid)
 160     {
 161       if (__chown (buf, uid, gid) < 0)
 162         goto helper;
 163     }
 164
 165   /* Make sure the permission mode is set to readable and writable by
 166      the owner, and writable by the group.  */
 167   mode_t mode = S_IRUSR|S_IWUSR|S_IWGRP;
 168 #else
 169   /* When built without pt_chown, we have delegated the creation of the
 170      pty node with the right group and permission mode to the kernel, and
 171      non-root users are unlikely to be able to change it. Therefore let's
 172      consider that POSIX enforcement is the responsibility of the whole
 173      system and not only the GNU libc. Thus accept different group or
 174      permission mode.  */
 175
 176   /* Make sure the permission is set to readable and writable by the
 177      owner.  For security reasons, make it writable by the group only
 178      when originally writable and when the group of the device is that
 179      special group.  */
 180   mode_t mode = S_IRUSR|S_IWUSR
 181                 |((st.st_gid == gid) ? (st.st_mode & S_IWGRP) : 0);
 182 #endif
 183
 184   if ((st.st_mode & ACCESSPERMS) != mode)
 185     {
 186       if (__chmod (buf, mode) < 0)
 187         goto helper;
 188     }
 189
 190   retval = 0;
 191   goto cleanup;
 192
 193   /* We have to use the helper program if it is available.  */
 194  helper:;
 195
 196 #if HAVE_PT_CHOWN
 197   pid_t pid = __fork ();
 198   if (pid == -1)
 199     goto cleanup;
 200   else if (pid == 0)
 201     {
 202       /* Disable core dumps.  */
 203       struct rlimit rl = { 0, 0 };
 204       __setrlimit (RLIMIT_CORE, &rl);
 205
 206       /* We pass the master pseudo terminal as file descriptor PTY_FILENO.  */
 207       if (fd != PTY_FILENO)
 208         if (__dup2 (fd, PTY_FILENO) < 0)
 209           _exit (FAIL_EBADF);
 210
 211 # ifdef CLOSE_ALL_FDS
 212       CLOSE_ALL_FDS ();
 213 # endif
 214
 215       execle (_PATH_PT_CHOWN, __basename (_PATH_PT_CHOWN), NULL, NULL);
 216       _exit (FAIL_EXEC);
 217     }
 218   else
 219     {
 220       int w;
 221
 222       if (__waitpid (pid, &w, 0) == -1)
 223         goto cleanup;
 224       if (!WIFEXITED (w))
 225         __set_errno (ENOEXEC);
 226       else
 227         switch (WEXITSTATUS (w))
 228           {
 229           case 0:
 230             retval = 0;
 231             break;
 232           case FAIL_EBADF:
 233             __set_errno (EBADF);
 234             break;
 235           case FAIL_EINVAL:
 236             __set_errno (EINVAL);
 237             break;
 238           case FAIL_EACCES:
 239             __set_errno (EACCES);
 240             break;
 241           case FAIL_EXEC:
 242             __set_errno (ENOEXEC);
 243             break;
 244           case FAIL_ENOMEM:
 245             __set_errno (ENOMEM);
 246             break;
 247
 248           default:
 249             assert(! "grantpt: internal error: invalid exit code from pt_chown");
 250           }
 251     }
 252 #endif
 253
 254  cleanup:
 255   if (buf != _buf)
 256     free (buf);
 257
 258   return retval;
 259 }
 260 libc_hidden_def (grantpt)