linux-kernel - Re: [PATCH] tipc: ensure skb->lock is initialised

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Date:   Tue, 9 Jul 2019 09:30:42 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "jon.maloy@...csson.com" <jon.maloy@...csson.com>,
        "ying.xue@...driver.com" <ying.xue@...driver.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tipc: ensure skb->lock is initialised



On 7/8/19 11:13 PM, Chris Packham wrote:
> On 9/07/19 8:43 AM, Chris Packham wrote:
>> On 8/07/19 8:18 PM, Eric Dumazet wrote:
>>>
>>>
>>> On 7/8/19 12:53 AM, Chris Packham wrote:
>>>> tipc_named_node_up() creates a skb list. It passes the list to
>>>> tipc_node_xmit() which has some code paths that can call
>>>> skb_queue_purge() which relies on the list->lock being initialised.
>>>> Ensure tipc_named_node_up() uses skb_queue_head_init() so that the lock
>>>> is explicitly initialised.
>>>>
>>>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>>>
>>> I would rather change the faulty skb_queue_purge() to __skb_queue_purge()
>>>
>>
>> Makes sense. I'll look at that for v2.
>>
> 
> Actually maybe not. tipc_rcast_xmit(), tipc_node_xmit_skb(), 
> tipc_send_group_msg(), __tipc_sendmsg(), __tipc_sendstream(), and 
> tipc_sk_timeout() all use skb_queue_head_init(). So my original change 
> brings tipc_named_node_up() into line with them.
> 
> I think it should be safe for tipc_node_xmit() to use 
> __skb_queue_purge() since all the callers seem to have exclusive access 
> to the list of skbs. It still seems that the callers should all use 
> skb_queue_head_init() for consistency.
> 

No, tipc does not use the list lock (it relies on the socket lock)
 and therefore should consistently use __skb_queue_head_init()
instead of skb_queue_head_init()

Using a spinlock to protect a local list makes no sense really,
it spreads false sense of correctness.

tipc_link_xmit() for example never acquires the spinlock,
yet uses skb_peek() and __skb_dequeue()

It is time to clean all this mess.