Bug 589613

This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release.  Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release.  This request is not yet committed for
inclusion.

http://post-office.corp.redhat.com/archives/rhkernel-list/2010-May/msg02057.html

Patch(es) available on kernel-2.6.32-29.el6

I am not probably triggering the bug correctly...

[root@dell-pesc430-03 ~]# uname -r
2.6.32-28.el6.x86_64
[root@dell-pesc430-03 ~]# gcc test.c 
[root@dell-pesc430-03 ~]# ./a.out 
(nil)

[root@dell-pesc430-03 ~]# uname -r
2.6.32-29.el6.x86_64
[root@dell-pesc430-03 ~]# gcc test.c 
[root@dell-pesc430-03 ~]# ./a.out 
(nil)

test.c:
#include <stdio.h>
#include <stdarg.h>

void vout (char * str, char * fmt, ...);

int main()
{
	char str[100];

	vout(str, "%p", NULL);
	printf("%s\n", str);
	return 0;
}

void vout (char * str, char * fmt, ...)
{
	va_list args;

	va_start(args, fmt);
	vsprintf(str, fmt, args);
	va_end(args);
}

It's about kernel internal implementation of vsprintf() not the user-space one from glibc so in my opinion you need to prepare a kernel module.

The changes were made to a kernel library file, which would require
that either a base kernel function, or a kernel module function, pass
a NULL string into one of the functions that would return a string
containing "(null)" instead of "<NULL>".  

But writing a kernel module that does something like that seems a bit
of overkill...  

If you just take the kernel src.rpm file, do an "rpmbuild -bp kernel.spec",
and then simply inspect the "linux-2.6.32.noarch/lib/vsprintf.c" file,
you can verify that the two former instances of "<NULL>" that were in
the string() and vbin_printf() functions have been replaced with "(null)".

VERIFIED Sanity only. 2.6.32-29 src code changed according the patch.
2.6.32-29 /lib/vsprintf.c:
 553  if ((unsigned long)s < PAGE_SIZE)
 554          s = "(null)";
 
1446  if ((unsigned long)save_str > (unsigned long)-PAGE_SIZE
1447                  || (unsigned long)save_str < PAGE_SIZE)
1448          save_str = "(null)";

Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.