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

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Message-ID: <20180317012935.GA6691@tigerII.localdomain>
Date:   Sat, 17 Mar 2018 10:29:35 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.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 (03/16/18 09:55), Petr Mladek wrote:
[..]
> I am not sure if it is worth it. I think that we would catch 99% of
> problems by checking the first byte.
> 
> This patch was motivated by a code clean up rather than bug reports.

OK. Then I think we really need this "the patch is just good enough" line
in the commit message and a big comment in the source code.

Another idea (just an idea) - for some pointers we know the address range
we are going to access and can check the first and the last byte. E.g. for
UUID it's check_access(ptr) and check_access(ptr + len), and so on. Won't
work for string() in general case, tho.

	-ss