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

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Date:   Tue, 9 Jul 2019 13:25:37 +0000
From:   Jon Maloy <jon.maloy@...csson.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        "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



> -----Original Message-----
> From: Eric Dumazet <eric.dumazet@...il.com>
> Sent: 9-Jul-19 03:31
> To: Chris Packham <Chris.Packham@...iedtelesis.co.nz>; Eric Dumazet
> <eric.dumazet@...il.com>; Jon Maloy <jon.maloy@...csson.com>;
> ying.xue@...driver.com; davem@...emloft.net
> Cc: netdev@...r.kernel.org; tipc-discussion@...ts.sourceforge.net; 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.

I agree with that.

> >
> 
> 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()

TIPC is using the list lock at message reception within the scope of tipc_sk_rcv()/tipc_skb_peek_port(), so it is fundamental that the lock always is correctly initialized.

> 
[...]
> 
> tipc_link_xmit() for example never acquires the spinlock, yet uses skb_peek()
> and __skb_dequeue()


You should look at tipc_node_xmit instead. Node local messages are sent directly to tipc_sk_rcv(), and never go through tipc_link_xmit()

Regards
///jon