printk: do not mangle valid userspace syslog prefixes (9d90c8d9) · Commits · 戴 / test

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;

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