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

From: Eric Dumazet <[email-masked]>
Date: Wed, 27 Jun 2018 12:33:19 -0700

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.