netdev - Re: [PATCH v2] netlink: do not set cb_running if dump's start() errs

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Message-Id: <20171009.102908.912133092174394094.davem@davemloft.net>
Date:   Mon, 09 Oct 2017 10:29:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     Jason@...c4.com
Cc:     johannes@...solutions.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] netlink: do not set cb_running if dump's start()
 errs

From: "Jason A. Donenfeld" <Jason@...c4.com>
Date: Mon,  9 Oct 2017 14:14:51 +0200

> It turns out that multiple places can call netlink_dump(), which means
> it's still possible to dereference partially initialized values in
> dump() that were the result of a faulty returned start().
> 
> This fixes the issue by calling start() _before_ setting cb_running to
> true, so that there's no chance at all of hitting the dump() function
> through any indirect paths.
> 
> It also moves the call to start() to be when the mutex is held. This has
> the nice side effect of serializing invocations to start(), which is
> likely desirable anyway. It also prevents any possible other races that
> might come out of this logic.
> 
> In testing this with several different pieces of tricky code to trigger
> these issues, this commit fixes all avenues that I'm aware of.
> 
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>

Applied and queued up for -stable.