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

Andy Shevchenko
2019-04-03T12:36:57Z

On Wed, Apr 03, 2019 at 02:17:39PM +0200, Rasmus Villemoes wrote:
> 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.

Missed that. I stand corrected.

> What
> you want is memdup_user_nul() - take a length-delimited user buffer and
> turn it into a nul-terminated string in kernel memory.

Good, we have a helper.

--
With Best Regards,
Andy Shevchenko