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Date: Thu, 15 Mar 2018 17:03:09 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        "Tobin C . Harding" <me@tobin.cc>, Joe Perches <joe@perches.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid
 pointers
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On (03/15/18 16:58), Sergey Senozhatsky wrote:
> On (03/14/18 15:09), Petr Mladek wrote:
> [..]
> > +static const char *check_pointer_access(const void *ptr)
> > +{
> > +	unsigned char byte;
> > +
> > +	if (!ptr)
> > +		return "(null)";
> > +
> > +	if (probe_kernel_read(&byte, ptr, 1))
>                                         ^^^^^
> Why one byte? 			     sizeof(ptr)?

I think there is a shorter version - probe_kernel_address(),
which, seems, was designed for this particular kind of stuff.

	void *p;

	if (probe_kernel_address(ptr, p))
		....

	-ss