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Commit 9d90c8d9 authored by Kay Sievers's avatar Kay Sievers Committed by Greg Kroah-Hartman
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printk: do not mangle valid userspace syslog prefixes 



printk: do not mangle valid userspace syslog prefixes with /dev/kmsg

Log messages passed to the kernel log by using /dev/kmsg or /dev/ttyprintk
might contain a syslog prefix including the syslog facility value.

This makes printk to recognize these headers properly, extract the real log
level from it to use, and add the prefix as a proper prefix to the
log buffer, instead of wrongly printing it as the log message text.

Before:
  $ echo '<14>text' > /dev/kmsg
  $ dmesg -r
  <4>[135159.594810] <14>text

After:
  $ echo '<14>text' > /dev/kmsg
  $ dmesg -r
  <14>[   50.750654] text

Cc: Lennart Poettering <lennart@poettering.net>
Signed-off-by: default avatarKay Sievers <kay.sievers@vrfy.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 54fad532

kernel/printk.c

+104 −34
Original line number Diff line number Diff line
@@ -498,6 +498,71 @@ static void _call_console_drivers(unsigned start, 
	}

}



/*

 * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the

 * lower 3 bit are the log level, the rest are the log facility. In case

 * userspace passes usual userspace syslog messages to /dev/kmsg or

 * /dev/ttyprintk, the log prefix might contain the facility. Printk needs

 * to extract the correct log level for in-kernel processing, and not mangle

 * the original value.

 *

 * If a prefix is found, the length of the prefix is returned. If 'level' is

 * passed, it will be filled in with the log level without a possible facility

 * value. If 'special' is passed, the special printk prefix chars are accepted

 * and returned. If no valid header is found, 0 is returned and the passed

 * variables are not touched.

 */

static size_t log_prefix(const char *p, unsigned int *level, char *special)

{

	unsigned int lev = 0;

	char sp = '\0';

	size_t len;



	if (p[0] != '<' || !p[1])

		return 0;

	if (p[2] == '>') {

		/* usual single digit level number or special char */

		switch (p[1]) {

		case '0' ... '7':

			lev = p[1] - '0';

			break;

		case 'c': /* KERN_CONT */

		case 'd': /* KERN_DEFAULT */

			sp = p[1];

			break;

		default:

			return 0;

		}

		len = 3;

	} else {

		/* multi digit including the level and facility number */

		char *endp = NULL;



		if (p[1] < '0' && p[1] > '9')

			return 0;



		lev = (simple_strtoul(&p[1], &endp, 10) & 7);

		if (endp == NULL || endp[0] != '>')

			return 0;

		len = (endp + 1) - p;

	}



	/* do not accept special char if not asked for */

	if (sp && !special)

		return 0;



	if (special) {

		*special = sp;

		/* return special char, do not touch level */

		if (sp)

			return len;

	}



	if (level)

		*level = lev;

	return len;

}



/*

 * Call the console drivers, asking them to write out

 * log_buf[start] to log_buf[end - 1].
@@ -513,13 +578,9 @@ static void call_console_drivers(unsigned start, unsigned end) 
	cur_index = start;

	start_print = start;

	while (cur_index != end) {

		if (msg_level < 0 && ((end - cur_index) > 2) &&

				LOG_BUF(cur_index + 0) == '<' &&

				LOG_BUF(cur_index + 1) >= '0' &&

				LOG_BUF(cur_index + 1) <= '7' &&

				LOG_BUF(cur_index + 2) == '>') {

			msg_level = LOG_BUF(cur_index + 1) - '0';

			cur_index += 3;

		if (msg_level < 0 && ((end - cur_index) > 2)) {

			/* strip log prefix */

			cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);

			start_print = cur_index;

		}

		while (cur_index != end) {
@@ -717,6 +778,8 @@ asmlinkage int vprintk(const char *fmt, va_list args) 
	unsigned long flags;

	int this_cpu;

	char *p;

	size_t plen;

	char special;



	boot_delay_msec();

	printk_delay();
@@ -757,45 +820,52 @@ asmlinkage int vprintk(const char *fmt, va_list args) 
	printed_len += vscnprintf(printk_buf + printed_len,

				  sizeof(printk_buf) - printed_len, fmt, args);





	p = printk_buf;



	/* Do we have a loglevel in the string? */

	if (p[0] == '<') {

		unsigned char c = p[1];

		if (c && p[2] == '>') {

			switch (c) {

			case '0' ... '7': /* loglevel */

				current_log_level = c - '0';

			/* Fallthrough - make sure we're on a new line */

			case 'd': /* KERN_DEFAULT */

	/* Read log level and handle special printk prefix */

	plen = log_prefix(p, &current_log_level, &special);

	if (plen) {

		p += plen;



		switch (special) {

		case 'c': /* Strip <c> KERN_CONT, continue line */

			plen = 0;

			break;

		case 'd': /* Strip <d> KERN_DEFAULT, start new line */

			plen = 0;

		default:

			if (!new_text_line) {

				emit_log_char('\n');

				new_text_line = 1;

			}

			/* Fallthrough - skip the loglevel */

			case 'c': /* KERN_CONT */

				p += 3;

				break;

			}

		}

	}



	/*

	 * Copy the output into log_buf. If the caller didn't provide

	 * appropriate log level tags, we insert them here

	 * the appropriate log prefix, we insert them here

	 */

	for (; *p; p++) {

		if (new_text_line) {

			/* Always output the token */

			new_text_line = 0;



			if (plen) {

				/* Copy original log prefix */

				int i;



				for (i = 0; i < plen; i++)

					emit_log_char(printk_buf[i]);

				printed_len += plen;

			} else {

				/* Add log prefix */

				emit_log_char('<');

				emit_log_char(current_log_level + '0');

				emit_log_char('>');

				printed_len += 3;

			new_text_line = 0;

			}



			if (printk_time) {

				/* Follow the token with the time */

				/* Add the current time stamp */

				char tbuf[50], *tp;

				unsigned tlen;

				unsigned long long t;