sysdeps/unix/sysv/linux/ttyname_r.c

   1 /* Copyright (C) 1991-2024 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 <errno.h>
  19 #include <limits.h>
  20 #include <stddef.h>
  21 #include <dirent.h>
  22 #include <sys/types.h>
  23 #include <sys/stat.h>
  24 #include <termios.h>
  25 #include <unistd.h>
  26 #include <string.h>
  27 #include <stdlib.h>
  28
  29 #include <fd_to_filename.h>
  30
  31 #include "ttyname.h"
  32
  33 static int getttyname_r (char *buf, size_t buflen,
  34                          const struct __stat64_t64 *mytty, int save,
  35                          int *dostat);
  36
  37 static int
  38 attribute_compat_text_section
  39 getttyname_r (char *buf, size_t buflen, const struct __stat64_t64 *mytty,
  40               int save, int *dostat)
  41 {
  42   struct __stat64_t64 st;
  43   DIR *dirstream;
  44   struct dirent64 *d;
  45   size_t devlen = strlen (buf);
  46
  47   dirstream = __opendir (buf);
  48   if (dirstream == NULL)
  49     {
  50       *dostat = -1;
  51       return errno;
  52     }
  53
  54   while ((d = __readdir64 (dirstream)) != NULL)
  55     if ((d->d_fileno == mytty->st_ino || *dostat)
  56         && strcmp (d->d_name, "stdin")
  57         && strcmp (d->d_name, "stdout")
  58         && strcmp (d->d_name, "stderr"))
  59       {
  60         char *cp;
  61         size_t needed = _D_EXACT_NAMLEN (d) + 1;
  62
  63         if (needed > buflen)
  64           {
  65             *dostat = -1;
  66             (void) __closedir (dirstream);
  67             __set_errno (ERANGE);
  68             return ERANGE;
  69           }
  70
  71         cp = __stpncpy (buf + devlen, d->d_name, needed);
  72         cp[0] = '\0';
  73
  74         if (__stat64_time64 (buf, &st) == 0
  75             && is_mytty (mytty, &st))
  76           {
  77             (void) __closedir (dirstream);
  78             __set_errno (save);
  79             return 0;
  80           }
  81       }
  82
  83   (void) __closedir (dirstream);
  84   __set_errno (save);
  85   /* It is not clear what to return in this case.  `isatty' says FD
  86      refers to a TTY but no entry in /dev has this inode.  */
  87   return ENOTTY;
  88 }
  89
  90 /* Store at most BUFLEN character of the pathname of the terminal FD is
  91    open on in BUF.  Return 0 on success,  otherwise an error number.  */
  92 int
  93 __ttyname_r (int fd, char *buf, size_t buflen)
  94 {
  95   struct fd_to_filename filename;
  96   struct __stat64_t64 st, st1;
  97   int dostat = 0;
  98   int doispty = 0;
  99   int save = errno;
 100
 101   /* Test for the absolute minimal size.  This makes life easier inside
 102      the loop.  */
 103   if (!buf)
 104     {
 105       __set_errno (EINVAL);
 106       return EINVAL;
 107     }
 108
 109   if (buflen < sizeof ("/dev/pts/"))
 110     {
 111       __set_errno (ERANGE);
 112       return ERANGE;
 113     }
 114
 115   /* isatty check, tcgetattr is used because it sets the correct
 116      errno (EBADF resp. ENOTTY) on error.  */
 117   struct termios term;
 118   if (__glibc_unlikely (__tcgetattr (fd, &term) < 0))
 119     return errno;
 120
 121   if (__fstat64_time64 (fd, &st) < 0)
 122     return errno;
 123
 124   /* We try using the /proc filesystem.  */
 125   ssize_t ret = __readlink (__fd_to_filename (fd, &filename), buf, buflen - 1);
 126   if (__glibc_unlikely (ret == -1 && errno == ENAMETOOLONG))
 127     {
 128       __set_errno (ERANGE);
 129       return ERANGE;
 130     }
 131
 132   if (__glibc_likely (ret != -1))
 133     {
 134 #define UNREACHABLE_LEN strlen ("(unreachable)")
 135       if (ret > UNREACHABLE_LEN
 136           && memcmp (buf, "(unreachable)", UNREACHABLE_LEN) == 0)
 137         {
 138           memmove (buf, buf + UNREACHABLE_LEN, ret - UNREACHABLE_LEN);
 139           ret -= UNREACHABLE_LEN;
 140         }
 141
 142       /* readlink need not terminate the string.  */
 143       buf[ret] = '\0';
 144
 145       /* Verify readlink result, fall back on iterating through devices.  */
 146       if (buf[0] == '/'
 147           && __stat64_time64 (buf, &st1) == 0
 148           && is_mytty (&st, &st1))
 149         return 0;
 150
 151       doispty = 1;
 152     }
 153
 154   /* Prepare the result buffer.  */
 155   memcpy (buf, "/dev/pts/", sizeof ("/dev/pts/"));
 156   buflen -= sizeof ("/dev/pts/") - 1;
 157
 158   if (__stat64_time64 (buf, &st1) == 0 && S_ISDIR (st1.st_mode))
 159     {
 160       ret = getttyname_r (buf, buflen, &st, save,
 161                           &dostat);
 162     }
 163   else
 164     {
 165       __set_errno (save);
 166       ret = ENOENT;
 167     }
 168
 169   if (ret && dostat != -1)
 170     {
 171       buf[sizeof ("/dev/") - 1] = '\0';
 172       buflen += sizeof ("pts/") - 1;
 173       ret = getttyname_r (buf, buflen, &st, save,
 174                           &dostat);
 175     }
 176
 177   if (ret && dostat != -1)
 178     {
 179       buf[sizeof ("/dev/") - 1] = '\0';
 180       dostat = 1;
 181       ret = getttyname_r (buf, buflen, &st,
 182                           save, &dostat);
 183     }
 184
 185   if (ret && doispty && is_pty (&st))
 186     {
 187       /* We failed to figure out the TTY's name, but we can at least
 188          signal that we did verify that it really is a PTY slave.
 189          This happens when we have inherited the file descriptor from
 190          a different mount namespace.  */
 191       __set_errno (ENODEV);
 192       return ENODEV;
 193     }
 194
 195   return ret;
 196 }
 197 libc_hidden_def (__ttyname_r)
 198 weak_alias (__ttyname_r, ttyname_r)