netdev - Re: [PATCH net-next] selftests/net: add txring

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Message-Id: <20181124.182248.866035142231867522.davem@davemloft.net>
Date:   Sat, 24 Nov 2018 18:22:48 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, willemb@...gle.com
Subject: Re: [PATCH net-next] selftests/net: add txring_overwrite

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Sat, 24 Nov 2018 21:09:26 -0500

> From: Willem de Bruijn <willemb@...gle.com>
> 
> Packet sockets with PACKET_TX_RING send skbs with user data in frags.
> 
> Before commit 5cd8d46ea156 ("packet: copy user buffers before orphan
> or clone") ring slots could be released prematurely, possibly allowing
> a process to overwrite data still in flight.
> 
> This test opens two packet sockets, one to send and one to read.
> The sender has a tx ring of one slot. It sends two packets with
> different payload, then reads both and verifies their payload.
> 
> Before the above commit, both receive calls return the same data as
> the send calls use the same buffer. From the commit, the clone
> needed for looping onto a packet socket triggers an skb_copy_ubufs
> to create a private copy. The separate sends each arrive correctly.
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Thanks for following up on this, applied.