Software Engineering Institute

The Linux kernel logging daemon (klogd) can be forced to hang if it receives a null byte in a log message from the Linux kernel. Please see the following bug report for more information:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=85478

This vulnerability causes klogd to go into an infinite loop, thus preventing further kernel log messages from being written to disk.

Upgrade to latest version of klogd for your Linux distribution.

The following workaround is taken from http://bugs.debian.org/cgi-bin/bugreport.cgi?archive=no&bug=85478:
The patch below contains a possible fix for this, by treating a null byte as a delimiter, equivalent to \. Additionally, the patch prevents LogLine from being invoked with a negative counter as an argument.

diff -u sysklogd-1.3.orig/klogd.c sysklogd-1.3/klogd.c
--- sysklogd-1.3.orig/klogd.c\t\t Sat Feb 10 13:04:06 2001
+++ sysklogd-1.3/klogd.c\t\t Sat Feb 10 12:58:11 2001
@@ -707,7 +707,7 @@
\t\t break; /* full line_buff or end of input buffer */
}

- if( *ptr == '\' ) /* newline */
+ if( *ptr == '\' || *ptr == '\0') /* newline or null terminator */
{
ptr++;\t\t /* skip newline */
space -= 1;
@@ -877,8 +877,10 @@
\t\t fprintf(stderr, "klogd: Error return from sys_sycall: " \
\t\t \t\t "%d - %s\", errno, strerror(errno));
}
-\t\t
-\t\t LogLine(log_buffer, rdcnt);
+ else
+ \t\t LogLine(log_buffer, rdcnt);
+
+
return;
}

@@ -902,8 +904,8 @@
\t\t Syslog(LOG_ERR, "Cannot read proc file system: %d - %s.", \
\t\t errno, strerror(errno));
}
-\t\t
-\t\t LogLine(log_buffer, rdcnt);
+ else
+ \t\t \t\t LogLine(log_buffer, rdcnt);

return;
}