linux-kernel - Re: [PATCH v4 3/9] vsprintf: Do not check address of well-known strings

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Date:   Sat, 07 Apr 2018 17:12:35 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Petr Mladek <pmladek@...e.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/9] vsprintf: Do not check address of well-known
 strings

On Fri, 2018-04-06 at 11:15 +0200, Petr Mladek wrote:
> On Thu 2018-04-05 15:30:51, Rasmus Villemoes wrote:
> > On 2018-04-04 10:58, Petr Mladek wrote:
> > > We are going to check the address using probe_kernel_address(). It
> > > will
> > > be more expensive and it does not make sense for well known
> > > address.
> > > 
> > > This patch splits the string() function. The variant without the
> > > check
> > > is then used on locations that handle string constants or strings
> > > defined
> > > as local variables.
> > > 
> > > This patch does not change the existing behavior.
> > 
> > Please leave string() alone, except for moving the < PAGE_SIZE check
> > to
> > a new helper checked_string (feel free to find a better name), and
> > use
> > checked_string for handling %s and possibly the few other cases
> > where
> > we're passing a user-supplied pointer. That avoids cluttering the
> > entire
> > file with double-underscore calls, and e.g. in the %pO case, it's
> > easier
> > to understand why one uses two different *string() helpers if the
> > name
> > of one somehow conveys how it is different from the other.
> 
> I understand your reasoning. I thought about exactly this as well.
> My problem is that string() will then be unsafe. It might be dangerous
> when porting patches.

I agree with Rasmus, and your argument here from my point of view kinda
weak. Are we really going to backport this patches? Why? We lived w/o
them for a long time. What's changed now?

> Is _string() really that bad? 

I would think so.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy