release/src/router/busybox/sysklogd/klogd.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini klogd implementation for busybox
   4  *
   5  * Copyright (C) 2001 by Gennady Feldman <gfeldman@gena01.com>.
   6  * Changes: Made this a standalone busybox module which uses standalone
   7  * syslog() client interface.
   8  *
   9  * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
  10  *
  11  * Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
  12  *
  13  * "circular buffer" Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
  14  *
  15  * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
  16  *
  17  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  18  */
  19
  20 #include "libbb.h"
  21 #include <syslog.h>
  22
  23
  24 /* The Linux-specific klogctl(3) interface does not rely on the filesystem and
  25  * allows us to change the console loglevel. Alternatively, we read the
  26  * messages from _PATH_KLOG. */
  27
  28 #if ENABLE_FEATURE_KLOGD_KLOGCTL
  29
  30 # include <sys/klog.h>
  31
  32 static void klogd_open(void)
  33 {
  34         /* "Open the log. Currently a NOP" */
  35         klogctl(1, NULL, 0);
  36 }
  37
  38 static void klogd_setloglevel(int lvl)
  39 {
  40         /* "printk() prints a message on the console only if it has a loglevel
  41          * less than console_loglevel". Here we set console_loglevel = lvl. */
  42         klogctl(8, NULL, lvl);
  43 }
  44
  45 static int klogd_read(char *bufp, int len)
  46 {
  47         return klogctl(2, bufp, len);
  48 }
  49 # define READ_ERROR "klogctl(2) error"
  50
  51 static void klogd_close(void)
  52 {
  53         /* FYI: cmd 7 is equivalent to setting console_loglevel to 7
  54          * via klogctl(8, NULL, 7). */
  55         klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
  56         klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
  57 }
  58
  59 #else
  60
  61 # include <paths.h>
  62 # ifndef _PATH_KLOG
  63 #  ifdef __GNU__
  64 #   define _PATH_KLOG "/dev/klog"
  65 #  else
  66 #   error "your system's _PATH_KLOG is unknown"
  67 #  endif
  68 # endif
  69 # define PATH_PRINTK "/proc/sys/kernel/printk"
  70
  71 enum { klogfd = 3 };
  72
  73 static void klogd_open(void)
  74 {
  75         int fd = xopen(_PATH_KLOG, O_RDONLY);
  76         xmove_fd(fd, klogfd);
  77 }
  78
  79 static void klogd_setloglevel(int lvl)
  80 {
  81         FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
  82         if (fp) {
  83                 /* This changes only first value:
  84                  * "messages with a higher priority than this
  85                  * [that is, with numerically lower value]
  86                  * will be printed to the console".
  87                  * The other three values in this pseudo-file aren't changed.
  88                  */
  89                 fprintf(fp, "%u\n", lvl);
  90                 fclose(fp);
  91         }
  92 }
  93
  94 static int klogd_read(char *bufp, int len)
  95 {
  96         return read(klogfd, bufp, len);
  97 }
  98 # define READ_ERROR "read error"
  99
 100 static void klogd_close(void)
 101 {
 102         klogd_setloglevel(7);
 103         if (ENABLE_FEATURE_CLEAN_UP)
 104                 close(klogfd);
 105 }
 106
 107 #endif
 108
 109 char log_buffer[6 * 1024 + 1];  /* Big enough to not lose msgs at bootup */
 110 enum {
 111         KLOGD_LOGBUF_SIZE = sizeof(log_buffer),
 112         OPT_LEVEL      = (1 << 0),
 113         OPT_FOREGROUND = (1 << 1),
 114 };
 115
 116 /* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
 117  * because that's how they interpret word "default"
 118  * in the openlog() manpage:
 119  *      LOG_USER (default)
 120  *              generic user-level messages
 121  * and the fact that LOG_KERN is a constant 0.
 122  * glibc interprets it as "0 in openlog() call means 'use default'".
 123  * I think it means "if openlog wasn't called before syslog() is called,
 124  * use default".
 125  * Convincing glibc maintainers otherwise is, as usual, nearly impossible.
 126  * Should we open-code syslog() here to use correct facility?
 127  */
 128
 129 int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 130 int klogd_main(int argc UNUSED_PARAM, char **argv)
 131 {
 132         int i = 0;
 133         char *opt_c;
 134         int opt;
 135         int used;
 136         unsigned int cnt;
 137
 138         opt = getopt32(argv, "c:n", &opt_c);
 139         if (opt & OPT_LEVEL) {
 140                 /* Valid levels are between 1 and 8 */
 141                 i = xatou_range(opt_c, 1, 8);
 142         }
 143         if (!(opt & OPT_FOREGROUND)) {
 144                 bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
 145         }
 146
 147         logmode = LOGMODE_SYSLOG;
 148
 149         /* klogd_open() before openlog(), since it might use fixed fd 3,
 150          * and openlog() also may use the same fd 3 if we swap them:
 151          */
 152         klogd_open();
 153         openlog("kernel", 0, LOG_KERN);
 154         /*
 155          * glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
 156          * above. The logic behind this is that standard
 157          * http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
 158          * says the following about openlog and syslog:
 159          * "LOG_USER
 160          *  Messages generated by arbitrary processes.
 161          *  This is the default facility identifier if none is specified."
 162          *
 163          * I believe glibc misinterpreted this text as "if openlog's
 164          * third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
 165          * Whereas it was meant to say "if *syslog* is called with facility
 166          * 0 in its 1st parameter without prior call to openlog, then perform
 167          * implicit openlog(LOG_USER)".
 168          *
 169          * As a result of this, eh, feature, standard klogd was forced
 170          * to open-code its own openlog and syslog implementation (!).
 171          *
 172          * Note that prohibiting openlog(LOG_KERN) on libc level does not
 173          * add any security: any process can open a socket to "/dev/log"
 174          * and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
 175          *
 176          * Google code search tells me there is no widespread use of
 177          * openlog("foo", 0, 0), thus fixing glibc won't break userspace.
 178          *
 179          * The bug against glibc was filed:
 180          * bugzilla.redhat.com/show_bug.cgi?id=547000
 181          */
 182
 183         if (i)
 184                 klogd_setloglevel(i);
 185
 186         signal(SIGHUP, SIG_IGN);
 187         /* We want klogd_read to not be restarted, thus _norestart: */
 188         bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);
 189
 190         syslog(LOG_NOTICE, "klogd started: %s", bb_banner);
 191
 192         used = 0;
 193         cnt = 0;
 194         while (!bb_got_signal) {
 195                 int n;
 196                 int priority;
 197                 char *start;
 198                 char *eor;
 199
 200                 /* "2 -- Read from the log." */
 201                 start = log_buffer + used;
 202                 n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
 203                 if (n < 0) {
 204                         if (errno == EINTR)
 205                                 continue;
 206                         bb_perror_msg(READ_ERROR);
 207                         break;
 208                 }
 209                 start[n] = '\0';
 210                 eor = &start[n];
 211
 212                 /* Process each newline-terminated line in the buffer */
 213                 start = log_buffer;
 214                 while (1) {
 215                         char *newline = strchrnul(start, '\n');
 216
 217                         if (*newline == '\0') {
 218                                 /* This line is incomplete */
 219
 220                                 /* move it to the front of the buffer */
 221                                 overlapping_strcpy(log_buffer, start);
 222                                 used = newline - start;
 223                                 if (used < KLOGD_LOGBUF_SIZE-1) {
 224                                         /* buffer isn't full */
 225                                         break;
 226                                 }
 227                                 /* buffer is full, log it anyway */
 228                                 used = 0;
 229                                 newline = NULL;
 230                         } else {
 231                                 *newline++ = '\0';
 232                         }
 233
 234                         /* Extract the priority */
 235                         priority = LOG_INFO;
 236                         if (*start == '<') {
 237                                 start++;
 238                                 if (*start) {
 239                                         /* kernel never generates multi-digit prios */
 240                                         priority = (*start - '0');
 241                                         start++;
 242                                 }
 243                                 if (*start == '>')
 244                                         start++;
 245                         }
 246                         /* Log (only non-empty lines) */
 247                         if (*start) {
 248                                 syslog(priority, "%s", start);
 249                                 /* give syslog time to catch up */
 250                                 ++cnt;
 251                                 if ((cnt & 0x07) == 0 && (cnt < 300 || (eor - start) > 200))
 252                                         usleep(50 * 1000);
 253                         }
 254
 255                         if (!newline)
 256                                 break;
 257                         start = newline;
 258                 }
 259         }
 260
 261         klogd_close();
 262         syslog(LOG_NOTICE, "klogd: exiting");
 263         if (bb_got_signal)
 264                 kill_myself_with_sig(bb_got_signal);
 265         return EXIT_FAILURE;
 266 }