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Date:   Thu, 30 Mar 2023 10:00:40 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Bobby Eshleman <bobby.eshleman@bytedance.com>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Cong Wang <xiyou.wangcong@gmail.com>
Subject: Re: [PATCH net v3] virtio/vsock: fix leaks due to missing skb owner
Message-ID: <p6y6cwfywyi5apvn4cx5edob3n2zvyrmfvj6yss5szd24phgnt@gynsr43tsvan>
References: <20230327-vsock-fix-leak-v3-1-292cfc257531@bytedance.com>
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In-Reply-To: <20230327-vsock-fix-leak-v3-1-292cfc257531@bytedance.com>
Precedence: bulk

On Wed, Mar 29, 2023 at 04:51:58PM +0000, Bobby Eshleman wrote:
>This patch sets the skb owner in the recv and send path for virtio.
>
>For the send path, this solves the leak caused when
>virtio_transport_purge_skbs() finds skb->sk is always NULL and therefore
>never matches it with the current socket. Setting the owner upon
>allocation fixes this.
>
>For the recv path, this ensures correctness of accounting and also
>correct transfer of ownership in vsock_loopback (when skbs are sent from
>one socket and received by another).
>
>Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
>Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
>Reported-by: Cong Wang <xiyou.wangcong@gmail.com>
>Link: https://lore.kernel.org/all/ZCCbATwov4U+GBUv@pop-os.localdomain/
>---
>Changes in v3:
>- virtio/vsock: use skb_set_owner_sk_safe() instead of
>  skb_set_owner_{r,w}
>- virtio/vsock: reject allocating/receiving skb if sk_refcnt==0 and WARN_ONCE
>- Link to v2: https://lore.kernel.org/r/20230327-vsock-fix-leak-v2-1-f6619972dee0@bytedance.com
>
>Changes in v2:
>- virtio/vsock: add skb_set_owner_r to recv_pkt()
>- Link to v1: https://lore.kernel.org/r/20230327-vsock-fix-leak-v1-1-3fede367105f@bytedance.com
>---
> net/vmw_vsock/virtio_transport_common.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 957cdc01c8e8..c927dc302faa 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -94,6 +94,11 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> 					 info->op,
> 					 info->flags);
>
>+	if (info->vsk && !skb_set_owner_sk_safe(skb, sk_vsock(info->vsk))) {
>+		WARN_ONCE(1, "failed to allocate skb on vsock socket with sk_refcnt == 0\n");
>+		goto out;
>+	}
>+
> 	return skb;
>
> out:
>@@ -1294,6 +1299,11 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> 		goto free_pkt;
> 	}
>
>+	if (!skb_set_owner_sk_safe(skb, sk)) {
>+		WARN_ONCE(1, "receiving vsock socket has sk_refcnt == 0\n");
>+		goto free_pkt;
>+	}
>+

LGTM!

I would have put the condition inside WARN_ONCE() because I find it
more readable (e.g. WARN_ONCE(!skb_set_owner_sk_safe(skb, sk), ...),
but I don't have a strong opinion on that, so that's fine too:

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Thanks,
Stefano