linux-kernel - Re: [PATCH 3/6] bitmap_parselist: rework input string parser

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Date:   Tue, 26 Mar 2019 21:09:18 +0000
From:   Yuri Norov <ynorov@...vell.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Travis <travis@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/6] bitmap_parselist: rework input string parser

+ Mike Travis <travis@....com>
+ Thomas Gleixner <tglx@...utronix.de>

----------------------------------------------------------------------
On Tue, Mar 26, 2019 at 12:07:45AM +0300, Yury Norov wrote:
>> The requirement for this rework is to keep the __bitmap_parselist()
>> copy-less and single-pass but make it more readable and maintainable by
>> splitting into logical parts and removing explicit nested cycles and
>> opaque local variables.
>>
>> __bitmap_parselist() can parse userspace inputs and therefore we cannot
>> use simple_strtoul() to parse numbers.

> So, all above depends to what memory we access kernel / user space.
> Perhaps we can get copy of memory of a given size and then parse it in kernel space always?

> --
> With Best Regards,
> Andy Shevchenko

What I missed during rework is that we have only one caller of *parselist_user  -
it's write_irq_affinity() introduced by Mike Travis in kernel/irq/proc.c. It doesn't look
like a hot path as it's file operations handler. If no objections from Mike or Thomas,
I think it would make sense to copy_from_user() the userspace data at the beginning
in sake of simplicity of __bitmap_parselist(), as you suggested above.

Yury