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

[Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>]

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>
> >
> > Provide a uaccess helper that allows callers to copy a single line from
> > user memory. This is useful for debugfs write callbacks.
>
> 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.

Bart