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

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Message-ID: <20180315130117.7c2fb761@vmware.local.home>
Date:   Thu, 15 Mar 2018 13:01:17 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid
 pointers

On Thu, 15 Mar 2018 17:03:09 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:

> 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))
> 		....
>

Agreed.

-- Steve