linux-kernel - Re: [PATCH 5.8 regression fix] platform/x86: thinkpad_acpi: Revert: Use strndup_user() in dispatch_proc

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Date:   Tue, 14 Jul 2020 11:33:52 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
        Thinkpad-acpi devel ML <ibm-acpi-devel@...ts.sourceforge.net>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5.8 regression fix] platform/x86: thinkpad_acpi: Revert:
 Use strndup_user() in dispatch_proc_write()

Hi,

On 7/14/20 10:27 AM, Andy Shevchenko wrote:
> On Tue, Jul 14, 2020 at 11:21 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
>> On Tue, Jul 14, 2020 at 11:15 AM Hans de Goede <hdegoede@...hat.com> wrote:
>>>
>>> Commit 35d13c7a0512 ("platform/x86: thinkpad_acpi: Use strndup_user()
>>> in dispatch_proc_write()") cleaned up dispatch_proc_write() by replacing
>>> the code to copy the passed in data from userspae with strndup_user().
>>
>> user space

Ack, do you want me to send a v2, or can you fix this up after applying.

>>> But strndup_user() expects a 0 terminated input buffer and the buffer
>>> passed to dispatch_proc_write() is NOT 0 terminated.
> 
> Second though, perhaps it's a simple wrong count parameter?
> strndup_user(..., min(count, PAGE_SIZE)) or so would work?

I honestly have not looked at a better fix and given that you've just come
up with 2 suggestions which may or may not work, combined with
where we are in the 5.8 cycle I believe it would be best to just
play it safe and go with the revert for 5.8.

If you then take a second attempt at cleaning this up for 5.9 and
send it to me, I can test it for you.

Regards,

Hans