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>
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138
kernel/printk.c
138
kernel/printk.c
@ -498,6 +498,71 @@ static void _call_console_drivers(unsigned start,
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}
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}
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}
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}
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/*
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* Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
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* lower 3 bit are the log level, the rest are the log facility. In case
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* userspace passes usual userspace syslog messages to /dev/kmsg or
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* /dev/ttyprintk, the log prefix might contain the facility. Printk needs
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* to extract the correct log level for in-kernel processing, and not mangle
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* the original value.
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*
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* If a prefix is found, the length of the prefix is returned. If 'level' is
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* passed, it will be filled in with the log level without a possible facility
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* value. If 'special' is passed, the special printk prefix chars are accepted
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* and returned. If no valid header is found, 0 is returned and the passed
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* variables are not touched.
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*/
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static size_t log_prefix(const char *p, unsigned int *level, char *special)
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{
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unsigned int lev = 0;
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char sp = '\0';
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size_t len;
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if (p[0] != '<' || !p[1])
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return 0;
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if (p[2] == '>') {
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/* usual single digit level number or special char */
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switch (p[1]) {
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case '0' ... '7':
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lev = p[1] - '0';
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break;
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case 'c': /* KERN_CONT */
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case 'd': /* KERN_DEFAULT */
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sp = p[1];
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break;
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default:
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return 0;
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}
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len = 3;
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} else {
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/* multi digit including the level and facility number */
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char *endp = NULL;
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if (p[1] < '0' && p[1] > '9')
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return 0;
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lev = (simple_strtoul(&p[1], &endp, 10) & 7);
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if (endp == NULL || endp[0] != '>')
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return 0;
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len = (endp + 1) - p;
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}
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/* do not accept special char if not asked for */
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if (sp && !special)
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return 0;
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if (special) {
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*special = sp;
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/* return special char, do not touch level */
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if (sp)
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return len;
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}
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if (level)
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*level = lev;
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return len;
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}
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/*
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/*
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* Call the console drivers, asking them to write out
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* Call the console drivers, asking them to write out
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* log_buf[start] to log_buf[end - 1].
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* log_buf[start] to log_buf[end - 1].
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@ -513,13 +578,9 @@ static void call_console_drivers(unsigned start, unsigned end)
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cur_index = start;
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cur_index = start;
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start_print = start;
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start_print = start;
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while (cur_index != end) {
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while (cur_index != end) {
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if (msg_level < 0 && ((end - cur_index) > 2) &&
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if (msg_level < 0 && ((end - cur_index) > 2)) {
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LOG_BUF(cur_index + 0) == '<' &&
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/* strip log prefix */
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LOG_BUF(cur_index + 1) >= '0' &&
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cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
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LOG_BUF(cur_index + 1) <= '7' &&
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LOG_BUF(cur_index + 2) == '>') {
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msg_level = LOG_BUF(cur_index + 1) - '0';
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cur_index += 3;
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start_print = cur_index;
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start_print = cur_index;
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}
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}
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while (cur_index != end) {
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while (cur_index != end) {
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@ -717,6 +778,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
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unsigned long flags;
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unsigned long flags;
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int this_cpu;
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int this_cpu;
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char *p;
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char *p;
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size_t plen;
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char special;
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boot_delay_msec();
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boot_delay_msec();
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printk_delay();
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printk_delay();
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@ -757,45 +820,52 @@ asmlinkage int vprintk(const char *fmt, va_list args)
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printed_len += vscnprintf(printk_buf + printed_len,
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printed_len += vscnprintf(printk_buf + printed_len,
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sizeof(printk_buf) - printed_len, fmt, args);
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sizeof(printk_buf) - printed_len, fmt, args);
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p = printk_buf;
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p = printk_buf;
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/* Do we have a loglevel in the string? */
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/* Read log level and handle special printk prefix */
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if (p[0] == '<') {
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plen = log_prefix(p, ¤t_log_level, &special);
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unsigned char c = p[1];
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if (plen) {
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if (c && p[2] == '>') {
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p += plen;
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switch (c) {
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case '0' ... '7': /* loglevel */
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switch (special) {
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current_log_level = c - '0';
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case 'c': /* Strip <c> KERN_CONT, continue line */
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/* Fallthrough - make sure we're on a new line */
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plen = 0;
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case 'd': /* KERN_DEFAULT */
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break;
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if (!new_text_line) {
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case 'd': /* Strip <d> KERN_DEFAULT, start new line */
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emit_log_char('\n');
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plen = 0;
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new_text_line = 1;
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default:
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}
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if (!new_text_line) {
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/* Fallthrough - skip the loglevel */
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emit_log_char('\n');
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case 'c': /* KERN_CONT */
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new_text_line = 1;
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p += 3;
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break;
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}
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}
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}
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}
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}
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}
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/*
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/*
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* Copy the output into log_buf. If the caller didn't provide
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* Copy the output into log_buf. If the caller didn't provide
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* appropriate log level tags, we insert them here
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* the appropriate log prefix, we insert them here
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*/
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*/
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for ( ; *p; p++) {
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for (; *p; p++) {
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if (new_text_line) {
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if (new_text_line) {
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/* Always output the token */
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emit_log_char('<');
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emit_log_char(current_log_level + '0');
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emit_log_char('>');
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printed_len += 3;
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new_text_line = 0;
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new_text_line = 0;
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if (plen) {
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/* Copy original log prefix */
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int i;
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for (i = 0; i < plen; i++)
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emit_log_char(printk_buf[i]);
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printed_len += plen;
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} else {
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/* Add log prefix */
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emit_log_char('<');
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emit_log_char(current_log_level + '0');
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emit_log_char('>');
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printed_len += 3;
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}
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if (printk_time) {
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if (printk_time) {
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/* Follow the token with the time */
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/* Add the current time stamp */
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char tbuf[50], *tp;
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char tbuf[50], *tp;
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unsigned tlen;
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unsigned tlen;
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unsigned long long t;
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unsigned long long t;
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