Patch "Fix use after free in get_capset_info callback." has been added to the 4.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    Fix use after free in get_capset_info callback.

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fix-use-after-free-in-get_capset_info-callback.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit cc5451bf54ddb4335b8ca441d3f8c3212d2fb09e
Author: Doug Horn <doughorn@xxxxxxxxxx>
Date:   Wed Sep 2 14:08:25 2020 -0700

    Fix use after free in get_capset_info callback.
    
    [ Upstream commit e219688fc5c3d0d9136f8d29d7e0498388f01440 ]
    
    If a response to virtio_gpu_cmd_get_capset_info takes longer than
    five seconds to return, the callback will access freed kernel memory
    in vg->capsets.
    
    Signed-off-by: Doug Horn <doughorn@xxxxxxxxxx>
    Link: http://patchwork.freedesktop.org/patch/msgid/20200902210847.2689-2-gurchetansingh@xxxxxxxxxxxx
    Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 06496a1281622..476b9993b0682 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -113,8 +113,10 @@ static void virtio_gpu_get_capsets(struct virtio_gpu_device *vgdev,
 					 vgdev->capsets[i].id > 0, 5 * HZ);
 		if (ret == 0) {
 			DRM_ERROR("timed out waiting for cap set %d\n", i);
+			spin_lock(&vgdev->display_info_lock);
 			kfree(vgdev->capsets);
 			vgdev->capsets = NULL;
+			spin_unlock(&vgdev->display_info_lock);
 			return;
 		}
 		DRM_INFO("cap set %d: id %d, max-version %d, max-size %d\n",
diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 772a5a3b0ce1a..18e8fcad6690b 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -596,9 +596,13 @@ static void virtio_gpu_cmd_get_capset_info_cb(struct virtio_gpu_device *vgdev,
 	int i = le32_to_cpu(cmd->capset_index);
 
 	spin_lock(&vgdev->display_info_lock);
-	vgdev->capsets[i].id = le32_to_cpu(resp->capset_id);
-	vgdev->capsets[i].max_version = le32_to_cpu(resp->capset_max_version);
-	vgdev->capsets[i].max_size = le32_to_cpu(resp->capset_max_size);
+	if (vgdev->capsets) {
+		vgdev->capsets[i].id = le32_to_cpu(resp->capset_id);
+		vgdev->capsets[i].max_version = le32_to_cpu(resp->capset_max_version);
+		vgdev->capsets[i].max_size = le32_to_cpu(resp->capset_max_size);
+	} else {
+		DRM_ERROR("invalid capset memory.");
+	}
 	spin_unlock(&vgdev->display_info_lock);
 	wake_up(&vgdev->resp_wq);
 }