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

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Message-ID: <CACT4Y+bXsD3FjOYMnpfPz3PtUpNNkpLtxqmZPmnQuk=r2OSpDw@mail.gmail.com>
Date:   Thu, 28 Feb 2019 07:41:44 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.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 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 Rodrigo,

What are IGT tests? How can I run them?

>
> 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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