linux-kernel - Re: [PATCH v3] IB/sa: Resolving use-after-free in ib_nl_send

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Message-ID: <20200621071227.GA6698@unreal>
Date:   Sun, 21 Jun 2020 10:12:27 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Divya Indi <divya.indi@...cle.com>, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, Kaike Wan <kaike.wan@...el.com>,
        Gerd Rausch <gerd.rausch@...cle.com>,
        Håkon Bugge <haakon.bugge@...cle.com>,
        Srinivas Eeda <srinivas.eeda@...cle.com>,
        Rama Nichanamatlu <rama.nichanamatlu@...cle.com>,
        Doug Ledford <dledford@...hat.com>
Subject: Re: [PATCH v3] IB/sa: Resolving use-after-free in ib_nl_send_msg

On Wed, Jun 17, 2020 at 03:23:00PM -0300, Jason Gunthorpe wrote:
> On Wed, Jun 17, 2020 at 08:17:39AM +0300, Leon Romanovsky wrote:
> >
> > My thoughts that everything here hints me that state machine and
> > locking are implemented wrongly. In ideal world, the expectation
> > is that REQ message will have a state in it (PREPARED, SENT, ACK
> > e.t.c.) and list manipulations are done accordingly with proper
> > locks, while rdma_nl_multicast() is done outside of the locks.
>
> It can't be done outside the lock without creating races - once
> rdma_nl_multicast happens it is possible for the other leg of the
> operation to begin processing.

It means that the state machine is wrong, not complete.

>
> The list must be updated before this happens.
>
> What is missing here is refcounting - the lifetime model of this data
> is too implicit, but it is not worth adding I think

I have same feeling for now, but it will flip if new fixes be in this area.

Thanks

>
> Jason