login/login.c

   1 /* Copyright (C) 1996-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <limits.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <stdlib.h>
  25 #include <utmp.h>
  26
  27
  28 /* Return the result of ttyname in the buffer pointed to by TTY, which should
  29    be of length BUF_LEN.  If it is too long to fit in this buffer, a
  30    sufficiently long buffer is allocated using malloc, and returned in TTY.
  31    0 is returned upon success, -1 otherwise.  */
  32 static int
  33 tty_name (int fd, char **tty, size_t buf_len)
  34 {
  35   int rv;                       /* Return value.  0 = success.  */
  36   char *buf = *tty;             /* Buffer for ttyname, initially the user's. */
  37
  38   for (;;)
  39     {
  40       char *new_buf;
  41
  42       if (buf_len)
  43         {
  44           rv = ttyname_r (fd, buf, buf_len);
  45
  46           if (rv != 0 || memchr (buf, '\0', buf_len))
  47             /* We either got an error, or we succeeded and the
  48                returned name fit in the buffer.  */
  49             break;
  50
  51           /* Try again with a longer buffer.  */
  52           buf_len += buf_len;   /* Double it */
  53         }
  54       else
  55         /* No initial buffer; start out by mallocing one.  */
  56         buf_len = 128;          /* First time guess.  */
  57
  58       if (buf != *tty)
  59         /* We've already malloced another buffer at least once.  */
  60         new_buf = realloc (buf, buf_len);
  61       else
  62         new_buf = malloc (buf_len);
  63       if (! new_buf)
  64         {
  65           rv = -1;
  66           __set_errno (ENOMEM);
  67           break;
  68         }
  69       buf = new_buf;
  70     }
  71
  72   if (rv == 0)
  73     *tty = buf;         /* Return buffer to the user.  */
  74   else if (buf != *tty)
  75     free (buf);         /* Free what we malloced when returning an error.  */
  76
  77   return rv;
  78 }
  79 \f
  80 void
  81 login (const struct utmp *ut)
  82 {
  83 #ifdef PATH_MAX
  84   char _tty[PATH_MAX + UT_LINESIZE];
  85 #else
  86   char _tty[512 + UT_LINESIZE];
  87 #endif
  88   char *tty = _tty;
  89   int found_tty;
  90   const char *ttyp;
  91   struct utmp copy = *ut;
  92
  93   /* Fill in those fields we supply.  */
  94 #if _HAVE_UT_TYPE - 0
  95   copy.ut_type = USER_PROCESS;
  96 #endif
  97 #if _HAVE_UT_PID - 0
  98   copy.ut_pid = getpid ();
  99 #endif
 100
 101   /* Seek tty.  */
 102   found_tty = tty_name (STDIN_FILENO, &tty, sizeof (_tty));
 103   if (found_tty < 0)
 104     found_tty = tty_name (STDOUT_FILENO, &tty, sizeof (_tty));
 105   if (found_tty < 0)
 106     found_tty = tty_name (STDERR_FILENO, &tty, sizeof (_tty));
 107
 108   if (found_tty >= 0)
 109     {
 110       /* We only want to insert the name of the tty without path.
 111          But take care of name like /dev/pts/3.  */
 112       if (strncmp (tty, "/dev/", 5) == 0)
 113         ttyp = tty + 5;         /* Skip the "/dev/".  */
 114       else
 115         ttyp = basename (tty);
 116
 117       /* Position to record for this tty.  */
 118       strncpy (copy.ut_line, ttyp, UT_LINESIZE);
 119
 120       /* Tell that we want to use the UTMP file.  */
 121       if (utmpname (_PATH_UTMP) == 0)
 122         {
 123           /* Open UTMP file.  */
 124           setutent ();
 125
 126           /* Write the entry.  */
 127           pututline (&copy);
 128
 129           /* Close UTMP file.  */
 130           endutent ();
 131         }
 132
 133       if (tty != _tty)
 134         free (tty);             /* Free buffer malloced by tty_name.  */
 135     }
 136   else
 137     /* We provide a default value so that the output does not contain
 138        an random bytes in this field.  */
 139     strncpy (copy.ut_line, "???", UT_LINESIZE);
 140
 141   /* Update the WTMP file.  Here we have to add a new entry.  */
 142   updwtmp (_PATH_WTMP, &copy);
 143 }