On Mon, Sep 7, 2020 at 1:45 PM Andy Shevchenko
[off-list ref] wrote:

On Mon, Sep 07, 2020 at 12:28:05PM +0200, Bartosz Golaszewski wrote:

quoted

On Mon, Sep 7, 2020 at 12:19 PM Andy Shevchenko
[off-list ref] wrote:

quoted

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

quoted

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

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

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