netdev - Re: [PATCH net v2] net: sctp: wake up all assocs if sndbuf policy is per socket

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Date:	Tue, 08 Apr 2014 22:50:31 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	vyasevic@...hat.com
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org, tgraf@...g.ch, nhorman@...driver.com
Subject: Re: [PATCH net v2] net: sctp: wake up all assocs if sndbuf policy
 is per socket

On 04/08/2014 09:37 PM, Vlad Yasevich wrote:
> On 04/08/2014 03:04 PM, Daniel Borkmann wrote:
>> On 04/08/2014 08:46 PM, David Miller wrote:
>>>
>>> Daniel and Vlad, I'm about to send Linus a pull request.
>>>
>>> I know that you still need to fixup this SCTP change and it'll be
>>> in there, but I really need to get the changes in my tree staged
>>> so that I can do a set of -stable submissions.
>>>
>>> So please don't freak out, I know that this change still needs work
>>> and shouldn't go to -stable just yet :-)
>>
>> Noted, thanks. I think the issue is that in sctp_association_free()
>> we do a list_del(&asoc->asocs) and then flush sctp_outq_free() which
>> will then access on sctp_wfree() a poisoned entry. I think this
>> should be list_del_init() instead.
>
> Switching to list_del_init() will solve the crash, but will not address
> the issue.  You've just removed an association and need to notify others
> of available space.  You can't do that since you've been unlinked.
>
> We either need a rcu_style unlink, or detect the delete case and loop
> from the beginning.
>
> You can do #2 easily enough by looking at asoc->base.dead to decide
> where to start looping.

Agreed, I think #2 is better, so we can simply call and return with
sctp_write_space() if we see that the assoc is dead; I think SCTP is
doing too much deferring to RCU anyway. ;)
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