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From: Eric Biggers <ebiggers@kernel.org>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/vgem: fix use-after-free when drm_gem_handle_create() fails
Date: Tue, 26 Feb 2019 13:30:54 -0800
Message-ID: <20190226213053.GC218103@gmail.com> (raw)
In-Reply-To: <155121487959.17933.15702334870310780013@skylake-alporthouse-com>

On Tue, Feb 26, 2019 at 09:01:29PM +0000, Chris Wilson wrote:
> Quoting Eric Biggers (2019-02-26 20:47:26)
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > If drm_gem_handle_create() fails in vgem_gem_create(), then the
> > drm_vgem_gem_object is freed twice: once when the reference is dropped
> > by drm_gem_object_put_unlocked(), and again by __vgem_gem_destroy().
> > 
> > This was hit by syzkaller using fault injection.
> > 
> > Fix it by skipping the second free.
> > 
> > Reported-by: syzbot+e73f2fb5ed5a5df36d33@syzkaller.appspotmail.com
> > Fixes: 5ba6c9ff961a ("drm/vgem: Fix mmaping")
> 
> That's the wrong fixes line, it's
> Fixes: af33a9190d02 ("drm/vgem: Enable dmabuf import interfaces")
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Laura Abbott <labbott@redhat.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> Sadly I reviewed it so I'm still culpable, but the fix is correct as the
> put purposely frees it on error.
> 

You're right; I misread the code at that commit.
I'll resend with the correct tags.

> > Cc: stable@vger.kernel.org
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> 
> > ---
> >  drivers/gpu/drm/vgem/vgem_drv.c | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> > index 5930facd6d2d8..70646d9da1596 100644
> > --- a/drivers/gpu/drm/vgem/vgem_drv.c
> > +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> > @@ -189,15 +189,13 @@ static struct drm_gem_object *vgem_gem_create(struct drm_device *dev,
> >                 return ERR_CAST(obj);
> >  
> >         ret = drm_gem_handle_create(file, &obj->base, handle);
> > +
> >         drm_gem_object_put_unlocked(&obj->base);
> > +
> 
> The pattern in the other GEM drivers is not to have these extra
> newlines.
> 
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> 
> >         if (ret)
> > -               goto err;
> > +               return ERR_PTR(ret);
> >  
> >         return &obj->base;
> > -
> > -err:
> > -       __vgem_gem_destroy(obj);
> > -       return ERR_PTR(ret);
> >  }
> >  
> >  static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
> > -- 
> > 2.21.0.rc2.261.ga7da99ff1b-goog
> > 

  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <00000000000053fea105791276d8@google.com>
2018-10-29 11:51 ` KASAN: use-after-free Read in drm_gem_object_release Dmitry Vyukov
2019-02-26 20:47   ` [PATCH] drm/vgem: fix use-after-free when drm_gem_handle_create() fails Eric Biggers
2019-02-26 21:01     ` Chris Wilson
2019-02-26 21:30       ` Eric Biggers [this message]
2019-02-26 21:44         ` [PATCH v2] " Eric Biggers
2019-02-27 23:52           ` Laura Abbott
2019-03-04 23:24           ` Rodrigo Siqueira
2019-02-26 22:08         ` [PATCH] drm/vkms: " Eric Biggers
2019-02-26 22:14           ` Chris Wilson
2019-02-27 23:12           ` Rodrigo Siqueira
2019-02-28  6:41             ` Dmitry Vyukov
2019-03-04 23:23               ` Rodrigo Siqueira
2019-03-05 14:25                 ` Dmitry Vyukov
2019-03-10 15:36                   ` Rodrigo Siqueira
2019-02-27 13:23     ` [PATCH] drm/vgem: " Sasha Levin

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