summaryrefslogtreecommitdiff
path: root/sysklogd/klogd.c
blob: 4db72110d9d5e51c3a3f38c5b7cfb6ab38463240 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
/* vi: set sw=4 ts=4: */
/*
 * Mini klogd implementation for busybox
 *
 * Copyright (C) 2001 by Gennady Feldman <gfeldman@gena01.com>.
 * Changes: Made this a standalone busybox module which uses standalone
 * syslog() client interface.
 *
 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 *
 * Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
 *
 * "circular buffer" Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
 *
 * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config KLOGD
//config:	bool "klogd"
//config:	default y
//config:	help
//config:	  klogd is a utility which intercepts and logs all
//config:	  messages from the Linux kernel and sends the messages
//config:	  out to the 'syslogd' utility so they can be logged. If
//config:	  you wish to record the messages produced by the kernel,
//config:	  you should enable this option.
//config:
//config:comment "klogd should not be used together with syslog to kernel printk buffer"
//config:	depends on KLOGD && FEATURE_KMSG_SYSLOG
//config:
//config:config FEATURE_KLOGD_KLOGCTL
//config:	bool "Use the klogctl() interface"
//config:	default y
//config:	depends on KLOGD
//config:	select PLATFORM_LINUX
//config:	help
//config:	  The klogd applet supports two interfaces for reading
//config:	  kernel messages. Linux provides the klogctl() interface
//config:	  which allows reading messages from the kernel ring buffer
//config:	  independently from the file system.
//config:
//config:	  If you answer 'N' here, klogd will use the more portable
//config:	  approach of reading them from /proc or a device node.
//config:	  However, this method requires the file to be available.
//config:
//config:	  If in doubt, say 'Y'.

//applet:IF_KLOGD(APPLET(klogd, BB_DIR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_KLOGD) += klogd.o

//usage:#define klogd_trivial_usage
//usage:       "[-c N] [-n]"
//usage:#define klogd_full_usage "\n\n"
//usage:       "Kernel logger\n"
//usage:     "\n	-c N	Print to console messages more urgent than prio N (1-8)"
//usage:     "\n	-n	Run in foreground"

#include "libbb.h"
#include "common_bufsiz.h"
#include <syslog.h>


/* The Linux-specific klogctl(3) interface does not rely on the filesystem and
 * allows us to change the console loglevel. Alternatively, we read the
 * messages from _PATH_KLOG. */

#if ENABLE_FEATURE_KLOGD_KLOGCTL

# include <sys/klog.h>

static void klogd_open(void)
{
	/* "Open the log. Currently a NOP" */
	klogctl(1, NULL, 0);
}

static void klogd_setloglevel(int lvl)
{
	/* "printk() prints a message on the console only if it has a loglevel
	 * less than console_loglevel". Here we set console_loglevel = lvl. */
	klogctl(8, NULL, lvl);
}

static int klogd_read(char *bufp, int len)
{
	return klogctl(2, bufp, len);
}
# define READ_ERROR "klogctl(2) error"

static void klogd_close(void)
{
	/* FYI: cmd 7 is equivalent to setting console_loglevel to 7
	 * via klogctl(8, NULL, 7). */
	klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
	klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
}

#else

# ifndef _PATH_KLOG
#  ifdef __GNU__
#   define _PATH_KLOG "/dev/klog"
#  else
#   error "your system's _PATH_KLOG is unknown"
#  endif
# endif
# define PATH_PRINTK "/proc/sys/kernel/printk"

enum { klogfd = 3 };

static void klogd_open(void)
{
	int fd = xopen(_PATH_KLOG, O_RDONLY);
	xmove_fd(fd, klogfd);
}

static void klogd_setloglevel(int lvl)
{
	FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
	if (fp) {
		/* This changes only first value:
		 * "messages with a higher priority than this
		 * [that is, with numerically lower value]
		 * will be printed to the console".
		 * The other three values in this pseudo-file aren't changed.
		 */
		fprintf(fp, "%u\n", lvl);
		fclose(fp);
	}
}

static int klogd_read(char *bufp, int len)
{
	return read(klogfd, bufp, len);
}
# define READ_ERROR "read error"

static void klogd_close(void)
{
	klogd_setloglevel(7);
	if (ENABLE_FEATURE_CLEAN_UP)
		close(klogfd);
}

#endif

#define log_buffer bb_common_bufsiz1
enum {
	KLOGD_LOGBUF_SIZE = COMMON_BUFSIZE,
	OPT_LEVEL      = (1 << 0),
	OPT_FOREGROUND = (1 << 1),
};

/* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
 * because that's how they interpret word "default"
 * in the openlog() manpage:
 *      LOG_USER (default)
 *              generic user-level messages
 * and the fact that LOG_KERN is a constant 0.
 * glibc interprets it as "0 in openlog() call means 'use default'".
 * I think it means "if openlog wasn't called before syslog() is called,
 * use default".
 * Convincing glibc maintainers otherwise is, as usual, nearly impossible.
 * Should we open-code syslog() here to use correct facility?
 */

int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int klogd_main(int argc UNUSED_PARAM, char **argv)
{
	int i = 0;
	char *opt_c;
	int opt;
	int used;

	setup_common_bufsiz();

	opt = getopt32(argv, "c:n", &opt_c);
	if (opt & OPT_LEVEL) {
		/* Valid levels are between 1 and 8 */
		i = xatou_range(opt_c, 1, 8);
	}
	if (!(opt & OPT_FOREGROUND)) {
		bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
	}

	logmode = LOGMODE_SYSLOG;

	/* klogd_open() before openlog(), since it might use fixed fd 3,
	 * and openlog() also may use the same fd 3 if we swap them:
	 */
	klogd_open();
	openlog("kernel", 0, LOG_KERN);
	/*
	 * glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
	 * above. The logic behind this is that standard
	 * http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
	 * says the following about openlog and syslog:
	 * "LOG_USER
	 *  Messages generated by arbitrary processes.
	 *  This is the default facility identifier if none is specified."
	 *
	 * I believe glibc misinterpreted this text as "if openlog's
	 * third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
	 * Whereas it was meant to say "if *syslog* is called with facility
	 * 0 in its 1st parameter without prior call to openlog, then perform
	 * implicit openlog(LOG_USER)".
	 *
	 * As a result of this, eh, feature, standard klogd was forced
	 * to open-code its own openlog and syslog implementation (!).
	 *
	 * Note that prohibiting openlog(LOG_KERN) on libc level does not
	 * add any security: any process can open a socket to "/dev/log"
	 * and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
	 *
	 * Google code search tells me there is no widespread use of
	 * openlog("foo", 0, 0), thus fixing glibc won't break userspace.
	 *
	 * The bug against glibc was filed:
	 * bugzilla.redhat.com/show_bug.cgi?id=547000
	 */

	if (i)
		klogd_setloglevel(i);

	signal(SIGHUP, SIG_IGN);
	/* We want klogd_read to not be restarted, thus _norestart: */
	bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);

	syslog(LOG_NOTICE, "klogd started: %s", bb_banner);

	write_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");

	used = 0;
	while (!bb_got_signal) {
		int n;
		int priority;
		char *start;

		/* "2 -- Read from the log." */
		start = log_buffer + used;
		n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
		if (n < 0) {
			if (errno == EINTR)
				continue;
			bb_perror_msg(READ_ERROR);
			break;
		}
		start[n] = '\0';

		/* Process each newline-terminated line in the buffer */
		start = log_buffer;
		while (1) {
			char *newline = strchrnul(start, '\n');

			if (*newline == '\0') {
				/* This line is incomplete */

				/* move it to the front of the buffer */
				overlapping_strcpy(log_buffer, start);
				used = newline - start;
				if (used < KLOGD_LOGBUF_SIZE-1) {
					/* buffer isn't full */
					break;
				}
				/* buffer is full, log it anyway */
				used = 0;
				newline = NULL;
			} else {
				*newline++ = '\0';
			}

			/* Extract the priority */
			priority = LOG_INFO;
			if (*start == '<') {
				start++;
				if (*start)
					priority = strtoul(start, &start, 10);
				if (*start == '>')
					start++;
			}
			/* Log (only non-empty lines) */
			if (*start)
				syslog(priority, "%s", start);

			if (!newline)
				break;
			start = newline;
		}
	}

	klogd_close();
	syslog(LOG_NOTICE, "klogd: exiting");
	remove_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");
	if (bb_got_signal)
		kill_myself_with_sig(bb_got_signal);
	return EXIT_FAILURE;
}