netdev - Re: [PATCH net-next] net: preserve sock reference when scrubbing the skb.

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Message-ID: <096ada36-8e05-c330-e5b3-3f6fcc77aea2@gmail.com>
Date:   Wed, 27 Jun 2018 12:33:19 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Flavio Leitner <fbl@...hat.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Miller <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        NetFilter <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: preserve sock reference when scrubbing the
 skb.

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.