Re: [PATCH] vsock/virtio: Fix unsigned integer wrap around in virtio_transport_has_space()

[Stefano Garzarella]

On Mon, Dec 11, 2023 at 05:25:05PM +0300, Nikolay Kuratov wrote:
> We need to do signed arithmetic if we expect condition
> `if (bytes < 0)` to be possible
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE

We should add:

Fixes: 06a8fc78367d ("VSOCK: Introduce virtio_vsock_common.ko")

> Signed-off-by: Nikolay Kuratov <kniv@xxxxxxxxxxxxxx>
> ---
> net/vmw_vsock/virtio_transport_common.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index c8e162c9d1df..6df246b53260 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -843,7 +843,7 @@ static s64 virtio_transport_has_space(struct vsock_sock *vsk)
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> 	s64 bytes;
>
> -	bytes = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
> +	bytes = (s64)vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);

If we respect the credit, this should not happen. It can happen, though,
that the receiver changes its buffer size while we're communicating,
and if it reduces it, this could happen. So yes, we need to fix it!

Thanks!

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>

> 	if (bytes < 0)
> 		bytes = 0;
>
> --
> 2.34.1