netdev - Re: [PATCH net] sctp: assign assoc_id earlier in __sctp

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Message-Id: <20161107.131925.1448895624986454134.davem@davemloft.net>
Date:   Mon, 07 Nov 2016 13:19:25 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     marcelo.leitner@...il.com
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        vyasevich@...il.com, nhorman@...driver.com,
        syzkaller@...glegroups.com, kcc@...gle.com, glider@...gle.com,
        edumazet@...gle.com, dvyukov@...gle.com, andreyknvl@...gle.com
Subject: Re: [PATCH net] sctp: assign assoc_id earlier in __sctp_connect

From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Date: Thu,  3 Nov 2016 17:03:41 -0200

> sctp_wait_for_connect() currently already holds the asoc to keep it
> alive during the sleep, in case another thread release it. But Andrey
> Konovalov and Dmitry Vyukov reported an use-after-free in such
> situation.
> 
> Problem is that __sctp_connect() doesn't get a ref on the asoc and will
> do a read on the asoc after calling sctp_wait_for_connect(), but by then
> another thread may have closed it and the _put on sctp_wait_for_connect
> will actually release it, causing the use-after-free.
> 
> Fix is, instead of doing the read after waiting for the connect, do it
> before so, and avoid this issue as the socket is still locked by then.
> There should be no issue on returning the asoc id in case of failure as
> the application shouldn't trust on that number in such situations
> anyway.
> 
> This issue doesn't exist in sctp_sendmsg() path.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

Applied and queued up for -stable, thanks.