Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid pointers

[kbuild test robot]

Hi Petr,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.16-rc5 next-20180314]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Petr-Mladek/vsprintf-Prevent-crash-when-dereferencing-invalid-pointers/20180315-214100
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)

>> lib/vsprintf.c:533:16: sparse: Using plain integer as NULL pointer
   lib/vsprintf.c:762:18: sparse: Variable length array is used.
   lib/vsprintf.c:765:38: sparse: cannot size expression
   lib/vsprintf.c:1532:23: sparse: incorrect type in assignment (different base types) @@    expected unsigned long [unsigned] [assigned] flags @@    got  long [unsigned] [assigned] flags @@
   lib/vsprintf.c:1532:23:    expected unsigned long [unsigned] [assigned] flags
   lib/vsprintf.c:1532:23:    got restricted gfp_t [usertype] <noident>

vim +533 lib/vsprintf.c

   522	
   523	static const char *check_pointer_access(const void *ptr)
   524	{
   525		unsigned char byte;
   526	
   527		if (!ptr)
   528			return "(null)";
   529	
   530		if (probe_kernel_read(&byte, ptr, 1))
   531			return "(efault)";
   532	
 > 533		return 0;
   534	}
   535	

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