linux-kernel - Re: [PATCH] drm/vkms: fix use-after-free when drm_gem_handle

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Date:   Mon, 4 Mar 2019 20:23:12 -0300
From:   Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        DRI <dri-devel@...ts.freedesktop.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] drm/vkms: fix use-after-free when
 drm_gem_handle_create() fails

On 02/28, Dmitry Vyukov wrote:
> On Thu, Feb 28, 2019 at 12:12 AM Rodrigo Siqueira
> <rodrigosiqueiramelo@...il.com> wrote:
> >
> > On 02/26, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@...gle.com>
> > >
> > > If drm_gem_handle_create() fails in vkms_gem_create(), then the
> > > vkms_gem_object is freed twice: once when the reference is dropped by
> > > drm_gem_object_put_unlocked(), and again by the extra calls to
> > > drm_gem_object_release() and kfree().
> > >
> > > Fix it by skipping the second release and free.
> > >
> > > This bug was originally found in the vgem driver by syzkaller using
> > > fault injection, but I noticed it's also present in the vkms driver.
> > >
> > > Fixes: 559e50fd34d1 ("drm/vkms: Add dumb operations")
> > > Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
> > > Cc: Haneen Mohammed <hamohammed.sa@...il.com>
> > > Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> > > Cc: Chris Wilson <chris@...is-wilson.co.uk>
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > > ---
> > >  drivers/gpu/drm/vkms/vkms_gem.c | 5 +----
> > >  1 file changed, 1 insertion(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
> > > index 138b0bb325cf9..69048e73377dc 100644
> > > --- a/drivers/gpu/drm/vkms/vkms_gem.c
> > > +++ b/drivers/gpu/drm/vkms/vkms_gem.c
> > > @@ -111,11 +111,8 @@ struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
> > >
> > >       ret = drm_gem_handle_create(file, &obj->gem, handle);
> > >       drm_gem_object_put_unlocked(&obj->gem);
> > > -     if (ret) {
> > > -             drm_gem_object_release(&obj->gem);
> > > -             kfree(obj);
> > > +     if (ret)
> > >               return ERR_PTR(ret);
> > > -     }
> > >
> > >       return &obj->gem;
> > >  }
> > > --
> > > 2.21.0.rc2.261.ga7da99ff1b-goog
> > >
> >
> > Hi,
> >
> > Thanks for your patch! :)
> >
> > The patch looks good for me. I also tested it under the IGT tests on my
> > local VM and everything was fine.

Hi,

Patch applied to drm-misc-fixes.
 
> Hi Rodrigo,
> 
> What are IGT tests? How can I run them?

Hi Dmitry,

IGT is a test suite focused on DRM drivers.

You can clone the project using the link below:

  https://gitlab.freedesktop.org/drm/igt-gpu-tools.git

In the README, you will find the software dependencies. After you
install all the required package, just use:

 mkdir build && meson build && cd build && ninja

Finally, if you want to test VKMS, I recommend you to do it inside a VM.

Best Regards
Rodrigo Siqueira

> >
> > Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
> >
> > --
> > Rodrigo Siqueira
> > https://siqueira.tech
> > Graduate Student
> > Department of Computer Science
> > University of São Paulo
> >
> > --
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-- 
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of São Paulo

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