linux-kernel - Re: [PATCH] firmware_loader: use kernel credentials when reading firmware

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Date:   Mon, 4 Apr 2022 10:33:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Thiébaud Weksteen <tweek@...gle.com>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Alistair Delva <adelva@...gle.com>,
        Adam Shih <adamshih@...gle.com>, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firmware_loader: use kernel credentials when reading
 firmware

On Mon, Apr 04, 2022 at 03:46:42PM +1000, Thiébaud Weksteen wrote:
> Device drivers may decide to not load firmware when probed to avoid
> slowing down the boot process should the firmware filesystem not be
> available yet. In this case, the firmware loading request may be done
> when a device file associated with the driver is first accessed. The
> credentials of the userspace process accessing the device file may be
> used to validate access to the firmware files requested by the driver.
> Ensure that the kernel assumes the responsibility of reading the
> firmware.
> 
> This was observed on Android for a graphic driver loading their firmware
> when the device file (e.g. /dev/mali0) was first opened by userspace
> (i.e. surfaceflinger). The security context of surfaceflinger was used
> to validate the access to the firmware file (e.g.
> /vendor/firmware/mali.bin).
> 
> Because previous configurations were relying on the userspace fallback
> mechanism, the security context of the userspace daemon (i.e. ueventd)
> was consistently used to read firmware files. More devices are found to
> use the command line argument firmware_class.path which gives the kernel
> the opportunity to read the firmware directly, hence surfacing this
> misattribution.
> 
> Signed-off-by: Thiébaud Weksteen <tweek@...gle.com>
> ---
>  drivers/base/firmware_loader/main.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)

Is this a bugfix?  if so, what commit does this fix?  If not, how has
this never been a problem in the past (i.e. what changed to cause
problems?)

thanks,

greg k-h