linux-kernel - Re: [PATCH] vsock/virtio: Fix unsigned integer wrap around in virtio_transport_has

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Message-ID: <t6mnn7lyusvwt4knlxkgaajphhs6es5xr6hr7iixtwrfcljw67@foceocwkayk2>
Date:   Mon, 11 Dec 2023 16:45:09 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Nikolay Kuratov <kniv@...dex-team.ru>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        virtualization@...ts.linux.dev, kvm@...r.kernel.org
Subject: Re: [PATCH] vsock/virtio: Fix unsigned integer wrap around in
 virtio_transport_has_space()

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@...dex-team.ru>
>---
> 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@...hat.com>

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