linux-kernel - Re: [PATCH RESEND] drm/amd/display: avoid using null object of framebuffer

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Message-Id: <20240822073204.1618876-1-make24@iscas.ac.cn>
Date: Thu, 22 Aug 2024 15:32:04 +0800
From: Ma Ke <make24@...as.ac.cn>
To: alexdeucher@...il.com
Cc: HaoPing.Liu@....com,
	Xinhui.Pan@....com,
	airlied@...il.com,
	akpm@...ux-foundation.org,
	alexander.deucher@....com,
	amd-gfx@...ts.freedesktop.org,
	aurabindo.pillai@....com,
	christian.koenig@....com,
	daniel@...ll.ch,
	dri-devel@...ts.freedesktop.org,
	hamza.mahfooz@....com,
	joshua@...ggi.es,
	linux-kernel@...r.kernel.org,
	make24@...as.ac.cn,
	marek.olsak@....com,
	mwen@...lia.com,
	stable@...r.kernel.org
Subject: Re: [PATCH RESEND] drm/amd/display: avoid using null object of framebuffer

Alex Deucher<alexdeucher@...il.com> wrote:
> On Wed, Aug 21, 2024 at 3:45 AM Ma Ke <make24@...as.ac.cn> wrote:
> >
> > Instead of using state->fb->obj[0] directly, get object from framebuffer
> > by calling drm_gem_fb_get_obj() and return error code when object is
> > null to avoid using null object of framebuffer.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: 5d945cbcd4b1 ("drm/amd/display: Create a file dedicated to planes")
> > Signed-off-by: Ma Ke <make24@...as.ac.cn>
> > ---
> >  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> > index a83bd0331c3b..5cb11cc2d063 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> > @@ -28,6 +28,7 @@
> >  #include <drm/drm_blend.h>
> >  #include <drm/drm_gem_atomic_helper.h>
> >  #include <drm/drm_plane_helper.h>
> > +#include <drm/drm_gem_framebuffer_helper.h>
> >  #include <drm/drm_fourcc.h>
> >
> >  #include "amdgpu.h"
> > @@ -935,10 +936,14 @@ static int amdgpu_dm_plane_helper_prepare_fb(struct drm_plane *plane,
> >         }
> >
> >         afb = to_amdgpu_framebuffer(new_state->fb);
> > -       obj = new_state->fb->obj[0];
> > +       obj = drm_gem_fb_get_obj(new_state->fb, 0);
> 
> Is it possible for obj to be NULL here?
> 
> Alex
Thank you for your response to the vulnerability I submitted. Yes, we 
believe there is a similar issue. As described in CVE-2024-41093, the obj 
will return as NULL and lead to a dereferencing problem, and a similar 
issue exists in this code. The discovery of this problem was confirmed 
through manual review of the code and compilation testing.
--
Regards,

Ma Ke