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From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: Zack Rusin <zackr@vmware.com>,
	linux-graphics-maintainer@vmware.com, airlied@linux.ie,
	daniel@ffwll.ch, maarten.lankhorst@linux.intel.com,
	mripard@kernel.org, tzimmermann@suse.de
Cc: gregkh@linuxfoundation.org, intel-gfx@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	skhan@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Intel-gfx] [PATCH 3/3] drm/vmwgfx: fix potential UAF in vmwgfx_surface.c
Date: Fri, 23 Jul 2021 14:44:35 +0800	[thread overview]
Message-ID: <cb3ea66e-7f59-c057-06ea-7ddca4329a7c@gmail.com> (raw)
In-Reply-To: <b27a2e80-c912-15eb-e78b-c8b6f3993930@vmware.com>

On 23/7/21 3:17 am, Zack Rusin wrote:
> On 7/22/21 5:29 AM, Desmond Cheong Zhi Xi wrote:
>> drm_file.master should be protected by either drm_device.master_mutex
>> or drm_file.master_lookup_lock when being dereferenced. However,
>> drm_master_get is called on unprotected file_priv->master pointers in
>> vmw_surface_define_ioctl and vmw_gb_surface_define_internal.
>>
>> This is fixed by replacing drm_master_get with drm_file_get_master.
>>
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> 
> Reviewed-by: Zack Rusin <zackr@vmware.com>
> 
> Thanks for taking the time to fix this. Apart from the clear logic 
> error, do you happen to know under what circumstances would this be hit? 
> We have someone looking at writing some vmwgfx specific igt tests and I 
> was wondering if I could add this to the list.
> 
> z

Hi Zack,

Thanks for the review.

For some context, the use-after-free happens when there's a race between 
accessing the value of drm_file.master, and a call to 
drm_setmaster_ioctl. If drm_file is not the creator of master, then the 
ioctl allocates a new master for drm_file and puts the old master.

Thus for example, the old value of drm_file.master could be freed in 
between getting the value of file_priv->master, and the call to 
drm_master_get.

I'm not entirely sure whether this scenario is a good candidate for a test?

For further reference, the issue was originally caught by Syzbot here:
https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803

And from the logs it seems that the reproducer set up a race between 
DRM_IOCTL_GET_UNIQUE and DRM_IOCTL_SET_MASTER. So possibly a race 
between VMW_CREATE_SURFACE and DRM_IOCTL_SET_MASTER could trigger the 
same bug.

Best wishes,
Desmond

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  reply	other threads:[~2021-07-23  9:40 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-22  9:29 [Intel-gfx] [PATCH 0/3] drm, drm/vmwgfx: fixes and updates related to drm_master Desmond Cheong Zhi Xi
2021-07-22  9:29 ` [Intel-gfx] [PATCH 1/3] drm: use the lookup lock in drm_is_current_master Desmond Cheong Zhi Xi
2021-07-22 10:38   ` Daniel Vetter
2021-07-22 15:04     ` Boqun Feng
2021-07-22 19:02       ` Daniel Vetter
2021-07-23  7:16         ` Boqun Feng
2021-07-27 14:37     ` Peter Zijlstra
2021-07-29  7:00       ` Daniel Vetter
2021-07-29 14:32         ` Desmond Cheong Zhi Xi
2021-07-29 14:45           ` Peter Zijlstra
2021-07-22  9:29 ` [Intel-gfx] [PATCH 2/3] drm: clarify lifetime/locking for drm_master's lease fields Desmond Cheong Zhi Xi
2021-07-22 10:35   ` Daniel Vetter
2021-07-22 13:02     ` Desmond Cheong Zhi Xi
2021-07-22 14:17       ` Daniel Vetter
2021-07-22  9:29 ` [Intel-gfx] [PATCH 3/3] drm/vmwgfx: fix potential UAF in vmwgfx_surface.c Desmond Cheong Zhi Xi
2021-07-22 10:39   ` Daniel Vetter
2021-07-22 19:17   ` Zack Rusin
2021-07-23  6:44     ` Desmond Cheong Zhi Xi [this message]
2021-07-22 14:05 ` [Intel-gfx] ✗ Fi.CI.SPARSE: warning for drm, drm/vmwgfx: fixes and updates related to drm_master Patchwork
2021-07-22 14:34 ` [Intel-gfx] ✗ Fi.CI.BAT: failure " Patchwork
2021-07-27 17:42 ` [Intel-gfx] ✗ Fi.CI.BUILD: failure for drm, drm/vmwgfx: fixes and updates related to drm_master (rev2) Patchwork

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