Re: [PATCH 1/5] lib: make bitmap_parselist_user() a wrapper on bitmap_parselist()

Rasmus Villemoes
2019-04-03T12:17:46Z

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