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

[Bartosz Golaszewski]

On Mon, Sep 7, 2020 at 1:45 PM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
>
> On Mon, Sep 07, 2020 at 12:28:05PM +0200, Bartosz Golaszewski wrote:
> > On Mon, Sep 7, 2020 at 12:19 PM Andy Shevchenko
> > <andy.shevchenko@xxxxxxxxx> wrote:
> > >
> > > 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
> > >
> >
> > Sure, but this is pretty much what I do in getline_from_user(). If
> > anything we should port mtrr_write() to using getline_from_user() once
> > it's available upstream, no?
>
> But you may provide getline_from_user() as inline in the same header where
> strncpy_from_user() is declared. It will be like 3 LOCs?
>

May be more than that. I'll see what I can do.

Bart