linux-kernel - Re: [PATCH 5.10] gpu/i915: fix error return in mmap_offset

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Message-ID: <aN6YVtnJ3Guh43n5@intel.com>
Date: Thu, 2 Oct 2025 18:20:54 +0300
From: Ville Syrjälä <ville.syrjala@...ux.intel.com>
To: Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc: Alexandr Sapozhnkiov <alsp705@...il.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH 5.10] gpu/i915: fix error return in mmap_offset_attach()

On Thu, Oct 02, 2025 at 09:55:58AM -0400, Rodrigo Vivi wrote:
> On Thu, Oct 02, 2025 at 11:48:26AM +0300, Alexandr Sapozhnkiov wrote:
> > From: Alexandr Sapozhnikov <alsp705@...il.com>
> 
> About the subject, this is not just a 5.10 kernel issue.
> This code is the current code in our tip.
> So this needs to target drm-tip branch, and then Cc stable
> and perhaps a Fixes: tag.
> 
> > 
> > In the drm_vma_node_allow function, kmalloc may 
> > return NULL, in which case the file element will not be 
> > added to the mmo->vma_node list. It would be good to 
> > not ignore this event, but at least log an error message.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > Signed-off-by: Alexandr Sapozhnikov <alsp705@...il.com>
> > ---
> >  drivers/gpu/drm/i915/gem/i915_gem_mman.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> > index a2195e28b625..adaef8f09d59 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> > @@ -706,8 +706,11 @@ mmap_offset_attach(struct drm_i915_gem_object *obj,
> >  	mmo = insert_mmo(obj, mmo);
> >  	GEM_BUG_ON(lookup_mmo(obj, mmap_type) != mmo);
> >  out:
> > -	if (file)
> > -		drm_vma_node_allow_once(&mmo->vma_node, file);
> > +	if (file) {
> > +		err = drm_vma_node_allow_once(&mmo->vma_node, file);
> > +		if (err)
> 
> perhaps we also need to drm_vma_offset_remove here?
> I mean... honest question, doubt here. Is there any further clean-up needed?

Yeah, mmo->vma_node has already been linked to varius places here.
So this will lead to use-after-free in short order.

With the current code if this fails then I think all that ends up
happening is that subsequent mmap() will fail. Maybe that's just
fine?

> 
> > +			goto err;
> > +	}
> >  	return mmo;
> >  
> >  err:
> > -- 
> > 2.43.0
> > 

-- 
Ville Syrjälä
Intel