netdev - Re: [PATCHv2 net] sctp: check and update stream->out_curr when allocating stream

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Message-ID: <20190129120531.GC10665@localhost.localdomain>
Date:   Tue, 29 Jan 2019 10:05:32 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net, Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCHv2 net] sctp: check and update stream->out_curr when
 allocating stream_out

On Thu, Nov 29, 2018 at 02:42:56PM +0800, Xin Long wrote:
> Now when using stream reconfig to add out streams, stream->out
> will get re-allocated, and all old streams' information will
> be copied to the new ones and the old ones will be freed.
> 
> So without stream->out_curr updated, next time when trying to
> send from stream->out_curr stream, a panic would be caused.
> 
> This patch is to check and update stream->out_curr when
> allocating stream_out.
> 
> v1->v2:
>   - define fa_index() to get elem index from stream->out_curr.
> 
> Fixes: 5bbbbe32a431 ("sctp: introduce stream scheduler foundations")
> Reported-by: Ying Xu <yinxu@...hat.com>
> Reported-by: syzbot+e33a3a138267ca119c7d@...kaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@...il.com>

We are sort of mixing things up here. We have a bug on SCTP stack that
triggers panics. As good practices recommends, the code should be as
generic as possible and the SCTP-only was dropped in favor of a more
generic one, fixing rhashtables instead. Okay. But then we discovered
rhashtables are going away and we are now waiting on a restructing
to fix the panic. That's not good, especially because it cannot and
should not be backported into -stable trees.

That said, we should not wait for the restructuring to _implicitly_
fix the bug. We should pursuit both fixes here:
- Apply this patch, to fix SCTP stack and allow it to be easily
  backportable.
- Apply the generic fix, which is the restructuring, whenever it
  actually lands.

Thoughts?

Thanks,
Marcelo