Re: [PATCH 03/23] lib: uaccess: provide getline_from_user()

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Mon, Sep 7, 2020 at 1:05 PM Bartosz Golaszewski
<bgolaszewski@xxxxxxxxxxxx> wrote:
> On Fri, Sep 4, 2020 at 6:35 PM Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > On Fri, Sep 04, 2020 at 05:45:27PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>

> > Doesn't mm/util.c provides us something like this?
> > strndup_user()?
> >
>
> Yes, there's both strndup_user() as well as strncpy_from_user(). The
> problem is that they rely on the strings being NULL-terminated. This
> is not guaranteed for debugfs file_operations write callbacks. We need
> some helper that takes the minimum of bytes provided by userspace and
> the buffer size and figure out how many bytes to actually copy IMO.

Wouldn't this [1] approach work?

[1]: https://elixir.bootlin.com/linux/v5.9-rc3/source/arch/x86/kernel/cpu/mtrr/if.c#L93


-- 
With Best Regards,
Andy Shevchenko