On Mon, Sep 7, 2020 at 1:05 PM Bartosz Golaszewski
[off-list ref] wrote:

On Fri, Sep 4, 2020 at 6:35 PM Andy Shevchenko
[off-list ref] wrote:

quoted

On Fri, Sep 04, 2020 at 05:45:27PM +0200, Bartosz Golaszewski wrote:

quoted

From: Bartosz Golaszewski <redacted>

quoted

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