netdev - Re: [RFC net] net: stream: don't purge sk_error

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Date:   Tue, 14 Sep 2021 10:55:49 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     willemb@...gle.com, netdev@...r.kernel.org
Subject: Re: [RFC net] net: stream: don't purge sk_error_queue without holding
 its lock



On 9/14/21 9:56 AM, Jakub Kicinski wrote:

> Right, but then inet_sock_destruct() also purges the err queue, again.
> I was afraid of regressions but we could just remove the purging 
> from sk_stream_kill_queues(), and target net-next?
> 

Yes, this would be the safest thing.

>> If you think there is a bug, it must be fixed in another way.
>>
>> IMO, preventing err packets from a prior session being queued after a tcp_disconnect()
>> is rather hard. We should not even try (packets could be stuck for hours in a qdisc)
> 
> Indeed, we could rearrange the SOCK_DEAD check in sock_queue_err_skb()
> to skip queuing and put it under the err queue lock (provided we make
> sk_stream_kill_queues() take that lock as well). But seems like an
> overkill. I'd lean towards the existing patch or removing the purge from
> sk_stream_kill_queues(). LMK what you prefer, this is not urgent.
> 

The issue would really about the tcp_disconnect() case, 
followed by a reuse of the socket to establish another session.

In order to prevent polluting sk_error_queue with notifications
triggered by old packets (from prior flow), this would require
to record the socket cookie in skb, or something like that :/