From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next] net: preserve sock reference when scrubbing the
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Date: Wed, 27 Jun 2018 12:33:19 -0700
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Cc: Flavio Leitner <fbl@redhat.com>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        David Miller <davem@davemloft.net>,
        Florian Westphal <fw@strlen.de>,
        NetFilter <netfilter-devel@vger.kernel.org>
To: Cong Wang <xiyou.wangcong@gmail.com>,
        Eric Dumazet <eric.dumazet@gmail.com>
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On 06/27/2018 11:59 AM, Cong Wang wrote:

> 
> IIRC, this skb_orphan() was introduced much earlier than TSQ, probably
> from the beginning of veth.

Sigh

SO_SNDBUF was invented years ago before veth.

You focus on TSQ while it is only one of the many things that are broken.

> 
> Leaving the stack should be effectively equivalent to leaving the host,
> from the view of network isolation.
> 


Having a UDP socket being able to burn a cpu and fill a qdisc is a major bug.

Bu default (blocking send() syscalls) the following loop should
block the thread if socket sk_wmem_alloc hits sk_sndbuf, this is
the beauty of backpressure.

while (1)
    send(fd, ...);  

With skb_orphan(), sk_wmem_alloc will stay around 0, so the loop will burn a cpu
and fill a qdisc, eventually breaking "network isolation", since other sockets
might be unable to send a single packet.

If you have a concrete case where the skb_orphan() is needed, then you will have
to add a parameter to let the admin opt-in for this.