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    SubjectRe: [PATCH 03/23] lib: uaccess: provide getline_from_user()
    On Mon, Sep 7, 2020 at 12:19 PM Andy Shevchenko
    <andy.shevchenko@gmail.com> wrote:
    >
    > On Mon, Sep 7, 2020 at 1:05 PM Bartosz Golaszewski
    > <bgolaszewski@baylibre.com> wrote:
    > > On Fri, Sep 4, 2020 at 6:35 PM Andy Shevchenko
    > > <andriy.shevchenko@linux.intel.com> wrote:
    > > > On Fri, Sep 04, 2020 at 05:45:27PM +0200, Bartosz Golaszewski wrote:
    > > > > From: Bartosz Golaszewski <bgolaszewski@baylibre.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?

    Bart

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