drm/virtio: Ensure cached capset entries are valid before copying.

virtio_gpu_get_caps_ioctl could return success with invalid data if a
second caller to the function occurred after the entry was created in
virtio_gpu_cmd_get_capset but prior to the virtio_gpu_cmd_capset_cb
callback being called.  This could leak contents of memory as well
since the caps_cache allocation is done without zeroing.

Signed-off-by: David Riley <davidriley@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190605234423.11348-1-davidriley@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 8a17ef9..9f43b16 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -524,7 +524,6 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
        list_for_each_entry(cache_ent, &vgdev->cap_cache, head) {
                if (cache_ent->id == args->cap_set_id &&
                    cache_ent->version == args->cap_set_ver) {
-                       ptr = cache_ent->caps_cache;
                        spin_unlock(&vgdev->display_info_lock);
                        goto copy_exit;
                }
@@ -535,6 +534,7 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
        virtio_gpu_cmd_get_capset(vgdev, found_valid, args->cap_set_ver,
                                  &cache_ent);
 
+copy_exit:
        ret = wait_event_timeout(vgdev->resp_wq,
                                 atomic_read(&cache_ent->is_valid), 5 * HZ);
        if (!ret)
@@ -542,7 +542,6 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 
        ptr = cache_ent->caps_cache;
 
-copy_exit:
        if (copy_to_user(u64_to_user_ptr(args->addr), ptr, size))
                return -EFAULT;