drm/qxl: qxl_release use after free

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>
Link: http://patchwork.freedesktop.org/patch/msgid/fa17b338-66ae-f299-68fe-8d32419d9071@virtuozzo.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/drivers/gpu/drm/qxl/qxl_cmd.c b/drivers/gpu/drm/qxl/qxl_cmd.c
index fa8762d..05863b2 100644 (file)
--- 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 09583a0..91f398d 100644 (file)
--- 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 f8776d6..3599db0 100644 (file)
--- 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 8117a45..72f3f1b 100644 (file)
--- 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: