linux-kernel - Re: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution

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Message-ID: <20220123223030.ijdzrunduww76jiq@liuwe-devbox-debian-v2>
Date:   Sun, 23 Jan 2022 22:30:30 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Hu <weh@...rosoft.com>, Dexuan Cui <decui@...rosoft.com>,
        "drawat.floss@...il.com" <drawat.floss@...il.com>,
        hhei <hhei@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution

On Sun, Jan 23, 2022 at 10:27:56PM +0000, Michael Kelley (LINUX) wrote:
> From: Wei Liu <wei.liu@...nel.org> Sent: Sunday, January 23, 2022 1:56 PM
> > 
> > On Sun, Jan 16, 2022 at 09:53:06PM +0000, Haiyang Zhang wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Michael Kelley (LINUX) <mikelley@...rosoft.com>
> > > > Sent: Sunday, January 16, 2022 2:19 PM
> > > > To: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> > <haiyangz@...rosoft.com>; Stephen
> > > > Hemminger <sthemmin@...rosoft.com>; wei.liu@...nel.org; Wei Hu
> > <weh@...rosoft.com>; Dexuan
> > > > Cui <decui@...rosoft.com>; drawat.floss@...il.com; hhei <hhei@...hat.com>;
> > linux-
> > > > kernel@...r.kernel.org; linux-hyperv@...r.kernel.org; linux-
> > fbdev@...r.kernel.org; dri-
> > > > devel@...ts.freedesktop.org
> > > > Cc: Michael Kelley (LINUX) <mikelley@...rosoft.com>
> > > > Subject: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution
> > > >
> > > > In the WIN10 version of the Synthetic Video protocol with Hyper-V,
> > > > Hyper-V reports a list of supported resolutions as part of the protocol
> > > > negotiation. The driver calculates the maximum width and height from
> > > > the list of resolutions, and uses those maximums to validate any screen
> > > > resolution specified in the video= option on the kernel boot line.
> > > >
> > > > This method of validation is incorrect. For example, the list of
> > > > supported resolutions could contain 1600x1200 and 1920x1080, both of
> > > > which fit in an 8 Mbyte frame buffer.  But calculating the max width
> > > > and height yields 1920 and 1200, and 1920x1200 resolution does not fit
> > > > in an 8 Mbyte frame buffer.  Unfortunately, this resolution is accepted,
> > > > causing a kernel fault when the driver accesses memory outside the
> > > > frame buffer.
> > > >
> > > > Instead, validate the specified screen resolution by calculating
> > > > its size, and comparing against the frame buffer size.  Delete the
> > > > code for calculating the max width and height from the list of
> > > > resolutions, since these max values have no use.  Also add the
> > > > frame buffer size to the info message to aid in understanding why
> > > > a resolution might be rejected.
> > > >
> > > > Fixes: 67e7cdb4829d ("video: hyperv: hyperv_fb: Obtain screen resolution from Hyper-V
> > > > host")
> > > > Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> > [...]
> > >
> > > Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
> > >
> > 
> > Applied to hyperv-fixes. Thanks.
> 
> This fix got pulled into the fbdev/for-next tree by a new maintainer, Helge Deller.
> See https://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev.git/commit/?h=for-next&id=bcc48f8d980b12e66a3d59dfa1041667db971d86

OK. I will drop it from hyperv-fixes. Thanks for letting me know!

> 
> Michael