xen/blkback: correctly respond to unknown, non-native requests

If the frontend is using a non-native protocol (e.g., a 64-bit
frontend with a 32-bit backend) and it sent an unrecognized request,
the request was not translated and the response would have the
incorrect ID.  This may cause the frontend driver to behave
incorrectly or crash.

Since the ID field in the request is always in the same place,
regardless of the request type we can get the correct ID and make a
valid response (which will report BLKIF_RSP_EOPNOTSUPP).

This bug affected 64-bit SLES 11 guests when using a 32-bit backend.
This guest does a BLKIF_OP_RESERVED_1 (BLKIF_OP_PACKET in the SLES
source) and would crash in blkif_int() as the ID in the response would
be invalid.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: stable@vger.kernel.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 27 insertions, 4 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 6d1cc3df2ac6..1a0faf6370ca 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -679,6 +679,16 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
 	return err;
 }
 
+static int dispatch_other_io(struct xen_blkif *blkif,
+			     struct blkif_request *req,
+			     struct pending_req *pending_req)
+{
+	free_req(pending_req);
+	make_response(blkif, req->u.other.id, req->operation,
+		      BLKIF_RSP_EOPNOTSUPP);
+	return -EIO;
+}
+
 static void xen_blk_drain_io(struct xen_blkif *blkif)
 {
 	atomic_set(&blkif->drain, 1);
@@ -800,17 +810,30 @@ __do_block_io_op(struct xen_blkif *blkif)
 
 		/* Apply all sanity checks to /private copy/ of request. */
 		barrier();
-		if (unlikely(req.operation == BLKIF_OP_DISCARD)) {
+
+		switch (req.operation) {
+		case BLKIF_OP_READ:
+		case BLKIF_OP_WRITE:
+		case BLKIF_OP_WRITE_BARRIER:
+		case BLKIF_OP_FLUSH_DISKCACHE:
+			if (dispatch_rw_block_io(blkif, &req, pending_req))
+				goto done;
+			break;
+		case BLKIF_OP_DISCARD:
 			free_req(pending_req);
 			if (dispatch_discard_io(blkif, &req))
-				break;
-		} else if (dispatch_rw_block_io(blkif, &req, pending_req))
+				goto done;
+			break;
+		default:
+			if (dispatch_other_io(blkif, &req, pending_req))
+				goto done;
 			break;
+		}
 
 		/* Yield point for this unbounded loop. */
 		cond_resched();
 	}
-
+done:
 	return more_to_do;
 }