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

[Jon M. <jon...@er...>]

> -----Original Message-----
> From: Eric Dumazet <eri...@gm...>
> Sent: 9-Jul-19 03:31
> To: Chris Packham <Chr...@al...>; Eric Dumazet
> <eri...@gm...>; Jon Maloy <jon...@er...>;
> yin...@wi...; da...@da...
> Cc: ne...@vg...; tip...@li...; linux-
> ke...@vg...
> 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 <chr...@al...>
> >>>
> >>> 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