linux-kernel - [PATCH 4.9 24/62] vhost/vsock: fix incorrect used length reported to the guest

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Date:   Mon,  6 Dec 2021 15:56:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Halil Pasic <pasic@...ux.ibm.com>,
        Jason Wang <jasowang@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: [PATCH 4.9 24/62] vhost/vsock: fix incorrect used length reported to the guest

From: Stefano Garzarella <sgarzare@...hat.com>

commit 49d8c5ffad07ca014cfae72a1b9b8c52b6ad9cb8 upstream.

The "used length" reported by calling vhost_add_used() must be the
number of bytes written by the device (using "in" buffers).

In vhost_vsock_handle_tx_kick() the device only reads the guest
buffers (they are all "out" buffers), without writing anything,
so we must pass 0 as "used length" to comply virtio spec.

Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
Cc: stable@...r.kernel.org
Reported-by: Halil Pasic <pasic@...ux.ibm.com>
Suggested-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
Link: https://lore.kernel.org/r/20211122163525.294024-2-sgarzare@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>
Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/vhost/vsock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -406,7 +406,7 @@ static void vhost_vsock_handle_tx_kick(s
 		else
 			virtio_transport_free_pkt(pkt);

-		vhost_add_used(vq, head, sizeof(pkt->hdr) + len);
+		vhost_add_used(vq, head, 0);
 		added = true;
 	}