netdev - Re: [PATCH net-next] virtio-net: invoke zerocopy callback on xmit path if no tx napi

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Message-Id: <20170822.110108.343109469263087166.davem@davemloft.net>
Date:   Tue, 22 Aug 2017 11:01:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     mst@...hat.com
Cc:     jasowang@...hat.com, willemdebruijn.kernel@...il.com,
        den@...ipeden.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] virtio-net: invoke zerocopy callback on xmit
 path if no tx napi

From: "Michael S. Tsirkin" <mst@...hat.com>
Date: Tue, 22 Aug 2017 20:55:56 +0300

> Which reminds me that skb_linearize in net core seems to be
> fundamentally racy - I suspect that if skb is cloned, and someone is
> trying to use the shared frags while another thread calls skb_linearize,
> we get some use after free bugs which likely mostly go undetected
> because the corrupted packets mostly go on wire and get dropped
> by checksum code.

Indeed, it does assume that the skb from which the clone was made
never has it's geometry changed.

I don't think even the TCP retransmit queue has this guarantee.