netdev - Re: [PATCH] neighbour: purge nf_bridged skb from foreign device neigh

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Date: Mon, 8 Jan 2024 19:26:09 +0800
From: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To: Florian Westphal <fw@...len.de>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH] neighbour: purge nf_bridged skb from foreign device neigh



On 08/01/2024 19:15, Florian Westphal wrote:
> Pavel Tikhomirov <ptikhomirov@...tuozzo.com> wrote:
>> An skb can be added to a neigh->arp_queue while waiting for an arp
>> reply. Where original skb's skb->dev can be different to neigh's
>> neigh->dev. For instance in case of bridging dnated skb from one veth to
>> another, the skb would be added to a neigh->arp_queue of the bridge.
>>
>> There is no explicit mechanism that prevents the original skb->dev link
>> of such skb from being freed under us. For instance neigh_flush_dev does
>> not cleanup skbs from different device's neigh queue. But that original
>> link can be used and lead to crash on e.g. this stack:
>>
>> arp_process
>>    neigh_update
>>      skb = __skb_dequeue(&neigh->arp_queue)
>>        neigh_resolve_output(..., skb)
>>          ...
>>            br_nf_dev_xmit
>>              br_nf_pre_routing_finish_bridge_slow
>>                skb->dev = nf_bridge->physindev
>>                br_handle_frame_finish
>>
>> So let's improve neigh_flush_dev to also purge skbs when device
>> equal to their skb->nf_bridge->physindev gets destroyed.
> 
> Can we fix this by replacing physindev pointer with plain
> ifindex instead?  There are not too many places that need to
> peek into the original net_device struct, so I don't think
> the additional dev_get_by_index_rcu() would be an issue.

I will work on it, thanks for a good idea!

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.