From: Kay Sievers <kay.sievers@vrfy.org>

Date: Sun, 13 Mar 2011 02:19:51 +0000 (+0100)

Subject: printk: do not mangle valid userspace syslog prefixes

X-Git-Tag: v2.6.39-rc1~471^2

X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=9d90c8d9cde929cbc575098e825d7c29d9f45054

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: Kay Sievers <kay.sievers@vrfy.org>

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---

diff --git a/kernel/printk.c b/kernel/printk.c

index 2ddbdc7..5e3d042 100644

--- a/kernel/printk.c

+++ b/kernel/printk.c

@@ -499,6 +499,71 @@ 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].

  * The console_lock must be held.

@@ -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 */

-				if (!new_text_line) {

-					emit_log_char('\n');

-					new_text_line = 1;

-				}

-			/* Fallthrough - skip the loglevel */

-			case 'c': /* KERN_CONT */

-				p += 3;

-				break;

+	/* 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;

 			}

 		}

 	}

 	/*

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

-	 * appropriate log level tags, we insert them here

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

+	 * the appropriate log prefix, we insert them here

 	 */

-	for ( ; *p; p++) {

+	for (; *p; p++) {

 		if (new_text_line) {

-			/* Always output the token */

-			emit_log_char('<');

-			emit_log_char(current_log_level + '0');

-			emit_log_char('>');

-			printed_len += 3;

 			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;

+			}

+

 			if (printk_time) {

-				/* Follow the token with the time */

+				/* Add the current time stamp */

 				char tbuf[50], *tp;

 				unsigned tlen;

 				unsigned long long t;