Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure the order in which resources are rele

Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure the order in which resources are rele

[Vasily Averin]

On 4/21/20 11:43 AM, Gerd Hoffmann wrote:
> On Sat, Apr 18, 2020 at 02:39:17PM +0800, Caicai wrote:
>> When a qxl resource is released, the list that needs to be released is
>> fetched from the linked list ring and cleared. When you empty the list,
>> instead of trying to determine whether the ttm buffer object for each
>> qxl in the list is locked, you release the qxl object and remove the
>> element from the list until the list is empty. It was found that the
>> linked list was cleared first, and that the lock on the corresponding
>> ttm Bo for the QXL had not been released, so that the new qxl could not
>> be locked when it used the TTM.
> 
> So the dma_resv_reserve_shared() call in qxl_release_validate_bo() is
> unbalanced?  Because the dma_resv_unlock() call in
> qxl_release_fence_buffer_objects() never happens due to
> qxl_release_free_list() clearing the list beforehand?  Is that correct?

we observe similar issue: RHEL7 guests crashes in 
qxl_draw_opaque_fb()
 qxl_release_fence_buffer_objects() 

crashdump investigation shows that qlx_object was freed and reused,
so its original content was re-written.

At the same time qxl_device have empty release_idr,
ant there are no allocated qxl_bo_list entries.
i.e. qxl_release_free was really called.

> The only way I see for this to happen is that the guest is preempted
> between qxl_push_{cursor,command}_ring_release() and
> qxl_release_fence_buffer_objects() calls.  The host can complete the qxl
> command then, signal the guest, and the IRQ handler calls
> qxl_release_free_list() before qxl_release_fence_buffer_objects() runs.

We think the same: qxl_release was freed by garbage collector before
original thread had called qxl_release_fence_buffer_objects().

> Looking through the code I think it should be safe to simply swap the
> qxl_release_fence_buffer_objects() +
> qxl_push_{cursor,command}_ring_release() calls to close that race
> window.  Can you try that and see if it fixes the bug for you?

I'm going to prepare and test such patch but I have one question here:
qxl_push_*_ring_release can be called with  interruptible=true and fail
How to correctly handle this case? Is the hunk below correct from your POV?

--- a/drivers/gpu/drm/qxl/qxl_ioctl.c
+++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
@@ -261,12 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
                        apply_surf_reloc(qdev, &reloc_info[i]);
        }
 
+       qxl_release_fence_buffer_objects(release);
        ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
-       if (ret)
-               qxl_release_backoff_reserve_list(release);  <<<< ????
-       else
-               qxl_release_fence_buffer_objects(release);
-
 out_free_bos:
 out_free_release:


Thank you,
	Vasily Averin

Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure the order in which resources are rele

[Vasily Averin]

On 4/21/20 11:43 AM, Gerd Hoffmann wrote:
> On Sat, Apr 18, 2020 at 02:39:17PM +0800, Caicai wrote:
>> When a qxl resource is released, the list that needs to be released is
>> fetched from the linked list ring and cleared. When you empty the list,
>> instead of trying to determine whether the ttm buffer object for each
>> qxl in the list is locked, you release the qxl object and remove the
>> element from the list until the list is empty. It was found that the
>> linked list was cleared first, and that the lock on the corresponding
>> ttm Bo for the QXL had not been released, so that the new qxl could not
>> be locked when it used the TTM.
> 
> So the dma_resv_reserve_shared() call in qxl_release_validate_bo() is
> unbalanced?  Because the dma_resv_unlock() call in
> qxl_release_fence_buffer_objects() never happens due to
> qxl_release_free_list() clearing the list beforehand?  Is that correct?

we observe similar issue: RHEL7 guests crashes in 
qxl_draw_opaque_fb()
 qxl_release_fence_buffer_objects() 

crashdump investigation shows that qlx_object was freed and reused,
so its original content was re-written.

At the same time qxl_device have empty release_idr,
ant there are no allocated qxl_bo_list entries.
i.e. qxl_release_free was really called.

> The only way I see for this to happen is that the guest is preempted
> between qxl_push_{cursor,command}_ring_release() and
> qxl_release_fence_buffer_objects() calls.  The host can complete the qxl
> command then, signal the guest, and the IRQ handler calls
> qxl_release_free_list() before qxl_release_fence_buffer_objects() runs.

We think the same: qxl_release was freed by garbage collector before
original thread had called qxl_release_fence_buffer_objects().

> Looking through the code I think it should be safe to simply swap the
> qxl_release_fence_buffer_objects() +
> qxl_push_{cursor,command}_ring_release() calls to close that race
> window.  Can you try that and see if it fixes the bug for you?

I'm going to prepare and test such patch but I have one question here:
qxl_push_*_ring_release can be called with  interruptible=true and fail
How to correctly handle this case? Is the hunk below correct from your POV?

--- a/drivers/gpu/drm/qxl/qxl_ioctl.c
+++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
@@ -261,12 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
                        apply_surf_reloc(qdev, &reloc_info[i]);
        }
 
+       qxl_release_fence_buffer_objects(release);
        ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
-       if (ret)
-               qxl_release_backoff_reserve_list(release);  <<<< ????
-       else
-               qxl_release_fence_buffer_objects(release);
-
 out_free_bos:
 out_free_release:


Thank you,
	Vasily Averin
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Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure the order in which resources are rele

[Gerd Hoffmann]

  Hi,

> > The only way I see for this to happen is that the guest is preempted
> > between qxl_push_{cursor,command}_ring_release() and
> > qxl_release_fence_buffer_objects() calls.  The host can complete the qxl
> > command then, signal the guest, and the IRQ handler calls
> > qxl_release_free_list() before qxl_release_fence_buffer_objects() runs.
> 
> We think the same: qxl_release was freed by garbage collector before
> original thread had called qxl_release_fence_buffer_objects().

Ok, nice, I think we can consider the issue being analyzed then ;)

> > Looking through the code I think it should be safe to simply swap the
> > qxl_release_fence_buffer_objects() +
> > qxl_push_{cursor,command}_ring_release() calls to close that race
> > window.  Can you try that and see if it fixes the bug for you?
> 
> I'm going to prepare and test such patch but I have one question here:
> qxl_push_*_ring_release can be called with  interruptible=true and fail
> How to correctly handle this case? Is the hunk below correct from your POV?

Oh, right, the error code path will be quite different, checking ...

> --- a/drivers/gpu/drm/qxl/qxl_ioctl.c
> +++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
> @@ -261,12 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
>                         apply_surf_reloc(qdev, &reloc_info[i]);
>         }
>  
> +       qxl_release_fence_buffer_objects(release);
>         ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
> -       if (ret)
> -               qxl_release_backoff_reserve_list(release);  <<<< ????
> -       else
> -               qxl_release_fence_buffer_objects(release);
> -
>  out_free_bos:
>  out_free_release:
	if (ret)
		qxl_release_free(qdev, release);

[ code context added ]

qxl_release_free() checks whenever a release is fenced and signals the
fence in case it is so it doesn't wait for the signal forever.  So, yes,
I think qxl_release_free() should cleanup the release properly in any
case and the patch chunk should be correct.

take care,
  Gerd

Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure the order in which resources are rele

[Gerd Hoffmann]

  Hi,

> > The only way I see for this to happen is that the guest is preempted
> > between qxl_push_{cursor,command}_ring_release() and
> > qxl_release_fence_buffer_objects() calls.  The host can complete the qxl
> > command then, signal the guest, and the IRQ handler calls
> > qxl_release_free_list() before qxl_release_fence_buffer_objects() runs.
> 
> We think the same: qxl_release was freed by garbage collector before
> original thread had called qxl_release_fence_buffer_objects().

Ok, nice, I think we can consider the issue being analyzed then ;)

> > Looking through the code I think it should be safe to simply swap the
> > qxl_release_fence_buffer_objects() +
> > qxl_push_{cursor,command}_ring_release() calls to close that race
> > window.  Can you try that and see if it fixes the bug for you?
> 
> I'm going to prepare and test such patch but I have one question here:
> qxl_push_*_ring_release can be called with  interruptible=true and fail
> How to correctly handle this case? Is the hunk below correct from your POV?

Oh, right, the error code path will be quite different, checking ...

> --- a/drivers/gpu/drm/qxl/qxl_ioctl.c
> +++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
> @@ -261,12 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
>                         apply_surf_reloc(qdev, &reloc_info[i]);
>         }
>  
> +       qxl_release_fence_buffer_objects(release);
>         ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
> -       if (ret)
> -               qxl_release_backoff_reserve_list(release);  <<<< ????
> -       else
> -               qxl_release_fence_buffer_objects(release);
> -
>  out_free_bos:
>  out_free_release:
	if (ret)
		qxl_release_free(qdev, release);

[ code context added ]

qxl_release_free() checks whenever a release is fenced and signals the
fence in case it is so it doesn't wait for the signal forever.  So, yes,
I think qxl_release_free() should cleanup the release properly in any
case and the patch chunk should be correct.

take care,
  Gerd

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Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure the order in which resources are rele

[Gerd Hoffmann]

  Hi,

> > The only way I see for this to happen is that the guest is preempted
> > between qxl_push_{cursor,command}_ring_release() and
> > qxl_release_fence_buffer_objects() calls.  The host can complete the qxl
> > command then, signal the guest, and the IRQ handler calls
> > qxl_release_free_list() before qxl_release_fence_buffer_objects() runs.
> 
> We think the same: qxl_release was freed by garbage collector before
> original thread had called qxl_release_fence_buffer_objects().

Ok, nice, I think we can consider the issue being analyzed then ;)

> > Looking through the code I think it should be safe to simply swap the
> > qxl_release_fence_buffer_objects() +
> > qxl_push_{cursor,command}_ring_release() calls to close that race
> > window.  Can you try that and see if it fixes the bug for you?
> 
> I'm going to prepare and test such patch but I have one question here:
> qxl_push_*_ring_release can be called with  interruptible=true and fail
> How to correctly handle this case? Is the hunk below correct from your POV?

Oh, right, the error code path will be quite different, checking ...

> --- a/drivers/gpu/drm/qxl/qxl_ioctl.c
> +++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
> @@ -261,12 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
>                         apply_surf_reloc(qdev, &reloc_info[i]);
>         }
>  
> +       qxl_release_fence_buffer_objects(release);
>         ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
> -       if (ret)
> -               qxl_release_backoff_reserve_list(release);  <<<< ????
> -       else
> -               qxl_release_fence_buffer_objects(release);
> -
>  out_free_bos:
>  out_free_release:
	if (ret)
		qxl_release_free(qdev, release);

[ code context added ]

qxl_release_free() checks whenever a release is fenced and signals the
fence in case it is so it doesn't wait for the signal forever.  So, yes,
I think qxl_release_free() should cleanup the release properly in any
case and the patch chunk should be correct.

take care,
  Gerd

[PATCH] drm/qxl: qxl_release use after free

[Vasily Averin]

qxl_release should not be accesses after qxl_push_*_ring_release() calls:
userspace driver can process submitted command quickly, move qxl_release
into release_ring, generate interrupt and trigger garbage collector.

It can lead to crashes in qxl driver or trigger memory corruption
in some kmalloc-192 slab object

Gerd Hoffmann proposes to swap the qxl_release_fence_buffer_objects() +
qxl_push_{cursor,command}_ring_release() calls to close that race window.

cc: stable@vger.kernel.org
Fixes: f64122c1f6ad ("drm: add new QXL driver. (v1.4)")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 drivers/gpu/drm/qxl/qxl_cmd.c     | 5 ++---
 drivers/gpu/drm/qxl/qxl_display.c | 6 +++---
 drivers/gpu/drm/qxl/qxl_draw.c    | 2 +-
 drivers/gpu/drm/qxl/qxl_ioctl.c   | 5 +----
 4 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/qxl/qxl_cmd.c b/drivers/gpu/drm/qxl/qxl_cmd.c
index fa8762d15d0f..05863b253d68 100644
--- a/drivers/gpu/drm/qxl/qxl_cmd.c
+++ b/drivers/gpu/drm/qxl/qxl_cmd.c
@@ -500,8 +500,8 @@ int qxl_hw_surface_alloc(struct qxl_device *qdev,
 	/* no need to add a release to the fence for this surface bo,
 	   since it is only released when we ask to destroy the surface
 	   and it would never signal otherwise */
-	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
 
 	surf->hw_surf_alloc = true;
 	spin_lock(&qdev->surf_id_idr_lock);
@@ -543,9 +543,8 @@ int qxl_hw_surface_dealloc(struct qxl_device *qdev,
 	cmd->surface_id = id;
 	qxl_release_unmap(qdev, release, &cmd->release_info);
 
-	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
-
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index 09583a08e141..91f398d51cfa 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -510,8 +510,8 @@ static int qxl_primary_apply_cursor(struct drm_plane *plane)
 	cmd->u.set.visible = 1;
 	qxl_release_unmap(qdev, release, &cmd->release_info);
 
-	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 
 	return ret;
 
@@ -652,8 +652,8 @@ static void qxl_cursor_atomic_update(struct drm_plane *plane,
 	cmd->u.position.y = plane->state->crtc_y + fb->hot_y;
 
 	qxl_release_unmap(qdev, release, &cmd->release_info);
-	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 
 	if (old_cursor_bo != NULL)
 		qxl_bo_unpin(old_cursor_bo);
@@ -700,8 +700,8 @@ static void qxl_cursor_atomic_disable(struct drm_plane *plane,
 	cmd->type = QXL_CURSOR_HIDE;
 	qxl_release_unmap(qdev, release, &cmd->release_info);
 
-	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 }
 
 static void qxl_update_dumb_head(struct qxl_device *qdev,
diff --git a/drivers/gpu/drm/qxl/qxl_draw.c b/drivers/gpu/drm/qxl/qxl_draw.c
index f8776d60d08e..3599db096973 100644
--- a/drivers/gpu/drm/qxl/qxl_draw.c
+++ b/drivers/gpu/drm/qxl/qxl_draw.c
@@ -243,8 +243,8 @@ void qxl_draw_dirty_fb(struct qxl_device *qdev,
 	}
 	qxl_bo_kunmap(clips_bo);
 
-	qxl_push_command_ring_release(qdev, release, QXL_CMD_DRAW, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_command_ring_release(qdev, release, QXL_CMD_DRAW, false);
 
 out_release_backoff:
 	if (ret)
diff --git a/drivers/gpu/drm/qxl/qxl_ioctl.c b/drivers/gpu/drm/qxl/qxl_ioctl.c
index 8117a45b3610..72f3f1bbb40c 100644
--- a/drivers/gpu/drm/qxl/qxl_ioctl.c
+++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
@@ -261,11 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
 			apply_surf_reloc(qdev, &reloc_info[i]);
 	}
 
+	qxl_release_fence_buffer_objects(release);
 	ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
-	if (ret)
-		qxl_release_backoff_reserve_list(release);
-	else
-		qxl_release_fence_buffer_objects(release);
 
 out_free_bos:
 out_free_release:
-- 
2.17.1

[PATCH] drm/qxl: qxl_release use after free

[Vasily Averin]

qxl_release should not be accesses after qxl_push_*_ring_release() calls:
userspace driver can process submitted command quickly, move qxl_release
into release_ring, generate interrupt and trigger garbage collector.

It can lead to crashes in qxl driver or trigger memory corruption
in some kmalloc-192 slab object

Gerd Hoffmann proposes to swap the qxl_release_fence_buffer_objects() +
qxl_push_{cursor,command}_ring_release() calls to close that race window.

cc: stable@vger.kernel.org
Fixes: f64122c1f6ad ("drm: add new QXL driver. (v1.4)")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 drivers/gpu/drm/qxl/qxl_cmd.c     | 5 ++---
 drivers/gpu/drm/qxl/qxl_display.c | 6 +++---
 drivers/gpu/drm/qxl/qxl_draw.c    | 2 +-
 drivers/gpu/drm/qxl/qxl_ioctl.c   | 5 +----
 4 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/qxl/qxl_cmd.c b/drivers/gpu/drm/qxl/qxl_cmd.c
index fa8762d15d0f..05863b253d68 100644
--- a/drivers/gpu/drm/qxl/qxl_cmd.c
+++ b/drivers/gpu/drm/qxl/qxl_cmd.c
@@ -500,8 +500,8 @@ int qxl_hw_surface_alloc(struct qxl_device *qdev,
 	/* no need to add a release to the fence for this surface bo,
 	   since it is only released when we ask to destroy the surface
 	   and it would never signal otherwise */
-	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
 
 	surf->hw_surf_alloc = true;
 	spin_lock(&qdev->surf_id_idr_lock);
@@ -543,9 +543,8 @@ int qxl_hw_surface_dealloc(struct qxl_device *qdev,
 	cmd->surface_id = id;
 	qxl_release_unmap(qdev, release, &cmd->release_info);
 
-	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
-
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_command_ring_release(qdev, release, QXL_CMD_SURFACE, false);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index 09583a08e141..91f398d51cfa 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -510,8 +510,8 @@ static int qxl_primary_apply_cursor(struct drm_plane *plane)
 	cmd->u.set.visible = 1;
 	qxl_release_unmap(qdev, release, &cmd->release_info);
 
-	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 
 	return ret;
 
@@ -652,8 +652,8 @@ static void qxl_cursor_atomic_update(struct drm_plane *plane,
 	cmd->u.position.y = plane->state->crtc_y + fb->hot_y;
 
 	qxl_release_unmap(qdev, release, &cmd->release_info);
-	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 
 	if (old_cursor_bo != NULL)
 		qxl_bo_unpin(old_cursor_bo);
@@ -700,8 +700,8 @@ static void qxl_cursor_atomic_disable(struct drm_plane *plane,
 	cmd->type = QXL_CURSOR_HIDE;
 	qxl_release_unmap(qdev, release, &cmd->release_info);
 
-	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
 }
 
 static void qxl_update_dumb_head(struct qxl_device *qdev,
diff --git a/drivers/gpu/drm/qxl/qxl_draw.c b/drivers/gpu/drm/qxl/qxl_draw.c
index f8776d60d08e..3599db096973 100644
--- a/drivers/gpu/drm/qxl/qxl_draw.c
+++ b/drivers/gpu/drm/qxl/qxl_draw.c
@@ -243,8 +243,8 @@ void qxl_draw_dirty_fb(struct qxl_device *qdev,
 	}
 	qxl_bo_kunmap(clips_bo);
 
-	qxl_push_command_ring_release(qdev, release, QXL_CMD_DRAW, false);
 	qxl_release_fence_buffer_objects(release);
+	qxl_push_command_ring_release(qdev, release, QXL_CMD_DRAW, false);
 
 out_release_backoff:
 	if (ret)
diff --git a/drivers/gpu/drm/qxl/qxl_ioctl.c b/drivers/gpu/drm/qxl/qxl_ioctl.c
index 8117a45b3610..72f3f1bbb40c 100644
--- a/drivers/gpu/drm/qxl/qxl_ioctl.c
+++ b/drivers/gpu/drm/qxl/qxl_ioctl.c
@@ -261,11 +261,8 @@ static int qxl_process_single_command(struct qxl_device *qdev,
 			apply_surf_reloc(qdev, &reloc_info[i]);
 	}
 
+	qxl_release_fence_buffer_objects(release);
 	ret = qxl_push_command_ring_release(qdev, release, cmd->type, true);
-	if (ret)
-		qxl_release_backoff_reserve_list(release);
-	else
-		qxl_release_fence_buffer_objects(release);
 
 out_free_bos:
 out_free_release:
-- 
2.17.1

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Re: [PATCH] drm/qxl: qxl_release use after free

[Gerd Hoffmann]

On Wed, Apr 29, 2020 at 12:01:24PM +0300, Vasily Averin wrote:
> qxl_release should not be accesses after qxl_push_*_ring_release() calls:
> userspace driver can process submitted command quickly, move qxl_release
> into release_ring, generate interrupt and trigger garbage collector.
> 
> It can lead to crashes in qxl driver or trigger memory corruption
> in some kmalloc-192 slab object
> 
> Gerd Hoffmann proposes to swap the qxl_release_fence_buffer_objects() +
> qxl_push_{cursor,command}_ring_release() calls to close that race window.
> 
> cc: stable@vger.kernel.org
> Fixes: f64122c1f6ad ("drm: add new QXL driver. (v1.4)")
> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>

Pushed to drm-misc-fixes.

thanks,
  Gerd

Re: [PATCH] drm/qxl: qxl_release use after free

[Gerd Hoffmann]

On Wed, Apr 29, 2020 at 12:01:24PM +0300, Vasily Averin wrote:
> qxl_release should not be accesses after qxl_push_*_ring_release() calls:
> userspace driver can process submitted command quickly, move qxl_release
> into release_ring, generate interrupt and trigger garbage collector.
> 
> It can lead to crashes in qxl driver or trigger memory corruption
> in some kmalloc-192 slab object
> 
> Gerd Hoffmann proposes to swap the qxl_release_fence_buffer_objects() +
> qxl_push_{cursor,command}_ring_release() calls to close that race window.
> 
> cc: stable@vger.kernel.org
> Fixes: f64122c1f6ad ("drm: add new QXL driver. (v1.4)")
> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>

Pushed to drm-misc-fixes.

thanks,
  Gerd

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Re:Re: [PATCH 1/1] drm/qxl: add mutex_lock/mutex_unlock to ensure theorder in which resources are rele

[蔡兆鹏]

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