On 17.05.21 16:01, Jan Beulich wrote:

On 13.05.2021 12:02, Juergen Gross wrote:

quoted

In order to avoid a malicious backend being able to influence the local
copy of a request build the request locally first and then copy it to
the ring page instead of doing it the other way round as today.

Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <redacted>
with one remark/question:

quoted

@@ -703,6 +704,7 @@ static int blkif_queue_rw_req(struct request *req, 

struct blkfront_ring_info *ri

quoted

  {
  	struct blkfront_info *info = rinfo->dev_info;
  	struct blkif_request *ring_req, *extra_ring_req = NULL;
+	struct blkif_request *final_ring_req, *final_extra_ring_req;

Without setting final_extra_ring_req to NULL just like is done for
extra_ring_req, ...

quoted

@@ -840,10 +845,10 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
  	if (setup.segments)
  		kunmap_atomic(setup.segments);
  
-	/* Keep a private copy so we can reissue requests when recovering. */
-	rinfo->shadow[id].req = *ring_req;
+	/* Copy request(s) to the ring page. */
+	*final_ring_req = *ring_req;
  	if (unlikely(require_extra_req))
-		rinfo->shadow[extra_id].req = *extra_ring_req;
+		*final_extra_ring_req = *extra_ring_req;

... are you sure all supported compilers will recognize the
conditional use and not warn about use of a possibly uninitialized
variable?

Hmm, probably better safe than sorry. Will change it.


Juergen