netdev - Re: [PATCH bpf-next] bpf: test_bpf: add dummy dev->net for flow

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Date:   Thu, 27 Sep 2018 05:58:54 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Song Liu <songliubraving@...com>, netdev@...r.kernel.org
Cc:     daniel@...earbox.net, kernel-team@...com,
        Willem de Bruijn <willemb@...gle.com>,
        Petar Penkov <ppenkov@...gle.com>
Subject: Re: [PATCH bpf-next] bpf: test_bpf: add dummy dev->net for
 flow_dissector



On 09/27/2018 12:15 AM, Song Liu wrote:
> Latest changes in __skb_flow_dissect() assume skb->dev has valid nd_net.
> However, this is not true for test_bpf. As a result, test_bpf.ko crashes
> the system with the following stack trace:
> 

> +	dev_net_set(&dev, &net);

This is yet another fake stuff that will break some day, so many other things would
need to be setup properly in a real "struct net"

What about using the current net_ns ?

dev_net_set(&dev, current->nsproxy->net_ns);

This might be &init_net in the context of test_bpf(), so maybe simply use &init_net
to clearly state that test_bpf is not net ns fully ready.


> +	RCU_INIT_POINTER(net.flow_dissector_prog, NULL);

This really was not needed. Everything is already zero.

>  	skb->dev = &dev;
>  	skb->dev->ifindex = SKB_DEV_IFINDEX;
>  	skb->dev->type = SKB_DEV_TYPE;
>