linux-kernel - Re: [PATCH 1/5] lib: make bitmap_parselist_user() a wrapper on bitmap

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Date:   Wed, 3 Apr 2019 14:17:39 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Mike Travis <travis@....com>, Yury Norov <ynorov@...vell.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] lib: make bitmap_parselist_user() a wrapper on
 bitmap_parselist()

On 03/04/2019 13.17, Andy Shevchenko wrote:
> On Wed, Apr 03, 2019 at 02:15:22PM +0300, Andy Shevchenko wrote:
>> On Wed, Apr 03, 2019 at 07:45:36AM +0300, Yury Norov wrote:
>>> Currently we parse user data byte after byte which leads to
>>> overcomplification of parsing algorithm. The only user of
>>> bitmap_parselist_user() is not performance-critical, and so we
>>> can copy user data to kernel buffer and simply call
>>> bitmap_parselist(). This rework lets us unify and simplify
>>> bitmap_parselist() and bitmap_parselist_user(), which is done
>>> in the following patch.
>>
>>> +	buf = kmalloc(ulen + 1, GFP_KERNEL);
>>> +	if (!buf)
>>> +		return -ENOMEM;
>>> +
>>> +	buf[ulen] = 0;
>>> +
>>> +	ret = copy_from_user(buf, ubuf, ulen);
>>> +	if (ret)
>>> +		goto out;
>>
>> Why not memdup_user() ?
> 
> Even more precisely (for strings) strndup_user().
> 

But the user buffer is not nul-terminated, i.e. it's not a string. What
you want is memdup_user_nul() - take a length-delimited user buffer and
turn it into a nul-terminated string in kernel memory. And yes, please
use that.

Rasmus