linux-kernel - Re: [PATCH 03/23] lib: uaccess: provide getline_from

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Message-ID: <20200907114551.GV1891694@smile.fi.intel.com>
Date:   Mon, 7 Sep 2020 14:45:51 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-doc <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 03/23] lib: uaccess: provide getline_from_user()

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

-- 
With Best Regards,
Andy Shevchenko