login/login.c

   1 /* Copyright (C) 1996-2023 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 <limits.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <stdlib.h>
  24 #include <utmp.h>
  25 #include <shlib-compat.h>
  26
  27 /* Return the result of ttyname in the buffer pointed to by TTY, which should
  28    be of length BUF_LEN.  If it is too long to fit in this buffer, a
  29    sufficiently long buffer is allocated using malloc, and returned in TTY.
  30    0 is returned upon success, -1 otherwise.  */
  31 static int
  32 tty_name (int fd, char **tty, size_t buf_len)
  33 {
  34   int rv;                       /* Return value.  0 = success.  */
  35   char *buf = *tty;             /* Buffer for ttyname, initially the user's. */
  36
  37   for (;;)
  38     {
  39       char *new_buf;
  40
  41       if (buf_len)
  42         {
  43           rv = __ttyname_r (fd, buf, buf_len);
  44
  45           if (rv != 0 || memchr (buf, '\0', buf_len))
  46             /* We either got an error, or we succeeded and the
  47                returned name fit in the buffer.  */
  48             break;
  49
  50           /* Try again with a longer buffer.  */
  51           buf_len += buf_len;   /* Double it */
  52         }
  53       else
  54         /* No initial buffer; start out by mallocing one.  */
  55         buf_len = 128;          /* First time guess.  */
  56
  57       if (buf != *tty)
  58         /* We've already malloced another buffer at least once.  */
  59         new_buf = realloc (buf, buf_len);
  60       else
  61         new_buf = malloc (buf_len);
  62       if (! new_buf)
  63         {
  64           rv = -1;
  65           __set_errno (ENOMEM);
  66           break;
  67         }
  68       buf = new_buf;
  69     }
  70
  71   if (rv == 0)
  72     *tty = buf;         /* Return buffer to the user.  */
  73   else if (buf != *tty)
  74     free (buf);         /* Free what we malloced when returning an error.  */
  75
  76   return rv;
  77 }
  78 \f
  79 void
  80 __login (const struct utmp *ut)
  81 {
  82 #ifdef PATH_MAX
  83   char _tty[PATH_MAX + UT_LINESIZE];
  84 #else
  85   char _tty[512 + UT_LINESIZE];
  86 #endif
  87   char *tty = _tty;
  88   int found_tty;
  89   const char *ttyp;
  90   struct utmp copy = *ut;
  91
  92   /* Fill in those fields we supply.  */
  93   copy.ut_type = USER_PROCESS;
  94   copy.ut_pid = getpid ();
  95
  96   /* Seek tty.  */
  97   found_tty = tty_name (STDIN_FILENO, &tty, sizeof (_tty));
  98   if (found_tty < 0)
  99     found_tty = tty_name (STDOUT_FILENO, &tty, sizeof (_tty));
 100   if (found_tty < 0)
 101     found_tty = tty_name (STDERR_FILENO, &tty, sizeof (_tty));
 102
 103   if (found_tty >= 0)
 104     {
 105       /* We only want to insert the name of the tty without path.
 106          But take care of name like /dev/pts/3.  */
 107       if (strncmp (tty, "/dev/", 5) == 0)
 108         ttyp = tty + 5;         /* Skip the "/dev/".  */
 109       else
 110         ttyp = basename (tty);
 111
 112       /* Position to record for this tty.  */
 113       strncpy (copy.ut_line, ttyp, UT_LINESIZE);
 114
 115       /* Tell that we want to use the UTMP file.  */
 116       if (__utmpname (_PATH_UTMP) == 0)
 117         {
 118           /* Open UTMP file.  */
 119           __setutent ();
 120
 121           /* Write the entry.  */
 122           __pututline (&copy);
 123
 124           /* Close UTMP file.  */
 125           __endutent ();
 126         }
 127
 128       if (tty != _tty)
 129         free (tty);             /* Free buffer malloced by tty_name.  */
 130     }
 131   else
 132     /* We provide a default value so that the output does not contain
 133        an random bytes in this field.  */
 134     strncpy (copy.ut_line, "???", UT_LINESIZE);
 135
 136   /* Update the WTMP file.  Here we have to add a new entry.  */
 137   __updwtmp (_PATH_WTMP, &copy);
 138 }
 139 versioned_symbol (libc, __login, login, GLIBC_2_34);
 140 libc_hidden_ver (__login, login)
 141
 142 #if OTHER_SHLIB_COMPAT (libutil, GLIBC_2_0, GLIBC_2_34)
 143 compat_symbol (libutil, __login, login, GLIBC_2_0);
 144 #endif