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 11:27:43 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Hans de Goede <hdegoede@...hat.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()

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
>
> > 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?

> > So this change leads to strndup_user() copying some extra random bytes
> > from userspace till it hits a 0 byte.
> >
> > This commit reverts the change to use strndup_user() fixing the
> > buffer being passed to the ibm_struct.write() call back containing extra
> > junk at the end.
>
> Can we simply use memdup_user()?
> And thanks for catching this up!



-- 
With Best Regards,
Andy Shevchenko