wmpower/src/open_syslog_on_stderr.c

   1 /***************************************************************************
   2                    open_syslog_on_stderr.c  -  description
   3                              -------------------
   4     begin                : Feb 10 2003
   5     copyright            : (C) 2003,2004,2005 by Noberasco Michele
   6     e-mail               : noberasco.gnu@disi.unige.it
   7 ***************************************************************************/
   8
   9 /***************************************************************************
  10  *                                                                         *
  11  *   This program is free software; you can redistribute it and/or modify  *
  12  *   it under the terms of the GNU General Public License as published by  *
  13  *   the Free Software Foundation; either version 2 of the License, or     *
  14  *   (at your option) any later version.                                   *
  15  *                                                                         *
  16  *   This program is distributed in the hope that it will be useful,       *
  17  *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
  18  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
  19  *   GNU General Public License for more details.                          *
  20  *                                                                         *
  21  *   You should have received a copy of the GNU General Public License     *
  22  *   along with this program; if not, write to the                         *
  23  *   Free Software Foundation, Inc.,                                       *
  24  *   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.              *
  25  *                                                                         *
  26  ***************************************************************************/
  27
  28
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <unistd.h>
  33 #include <pthread.h>
  34 #include <syslog.h>
  35 #include <sys/types.h>
  36 #include <sys/stat.h>
  37
  38
  39
  40 /* this is the thread that will actually read
  41  * from our redirected stderr, forwarding to syslog
  42  */
  43 void syslog_writer(char *filename)
  44 {
  45         FILE *fp = fopen(filename, "r");
  46         char  buf[1024];
  47
  48         if (!fp)
  49         { /* we write this to stdout as stderr is probably compromised at this point */
  50                 printf("wmpower: syslog_writer thread: fatal error: unable to hook to main thread's stderr!\n");
  51                 abort();
  52         }
  53
  54         /* inititalize syslog writer */
  55         openlog("wmpower", 0, LOG_USER);
  56
  57         /* we remove it so that noone will tamper */
  58         unlink(filename);
  59
  60         while (1)
  61         {
  62                 fflush(NULL);
  63
  64                 while (fgets(buf, 1023, fp))
  65                         syslog(LOG_INFO, "%s", buf);
  66
  67                 sleep(1);
  68         }
  69 }
  70
  71 /*
  72  * Redirect writes to sterr on syslog...
  73  * we achieve this by starting a new thread, creating a file
  74  * that the father will write to, and the child read from,
  75  * rewriting it to syslog. Also, we unlink() the file as soon
  76  * as both father and child have it open, so that no other
  77  * process will be able to tamper with it.
  78  */
  79 void open_syslog_on_stderr(void)
  80 {
  81         pthread_t  thread;
  82         char      *filename;
  83         int        fd;
  84
  85         filename = (char*) malloc(19*sizeof(char));
  86
  87         if (!filename)
  88         {
  89                 fprintf(stderr, "wmpower: fatal error: failed allocating memory!\n");
  90                 abort();
  91         }
  92
  93         strcpy(filename, "/tmp/wmpowerXXXXXX");
  94
  95         fd = mkstemp(filename);
  96         if (fd == -1)
  97         {
  98                 fprintf(stderr, "wmpower: fatal error: could not create temporary file!\n");
  99                 abort();
 100         }
 101
 102         /* set file mode to 600 */
 103         if (chmod(filename, S_IRUSR|S_IWUSR))
 104         {
 105                 fprintf(stderr, "wmpower: fatal error: cannot chmod() file!\n");
 106                 abort();
 107         }
 108
 109         if (!freopen(filename, "w", stderr))
 110         {
 111                 fprintf(stderr, "wmpower: fatal error: unable to redirect stderr!\n");
 112                 abort();
 113         }
 114
 115         /* close the file descriptor as we have no need for it */
 116         close(fd);
 117
 118         /* spawn our syslog_writer baby */
 119         if (pthread_create(&thread, NULL, (void*)(&syslog_writer), filename))
 120         {
 121                 fprintf(stderr, "wmpower: fatal error: failed to create syslog-writer thread!\n");
 122                 abort();
 123         }
 124 }