netdev - Re: [PATCH net] xen-netback: avoid race that can lead to NULL pointer dereference

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Date:   Thu, 12 Dec 2019 18:10:41 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Paul Durrant <pdurrant@...zon.com>
Cc:     netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, Juergen Gross <jgross@...e.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Wei Liu <wei.liu@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net] xen-netback: avoid race that can lead to NULL
 pointer dereference

On Thu, Dec 12, 2019 at 12:37:23PM +0000, Paul Durrant wrote:
> Commit 2ac061ce97f4 ("xen/netback: cleanup init and deinit code")
> introduced a problem. In function xenvif_disconnect_queue(), the value of
> queue->rx_irq is zeroed *before* queue->task is stopped. Unfortunately that
> task may call notify_remote_via_irq(queue->rx_irq) and calling that
> function with a zero value results in a NULL pointer dereference in
> evtchn_from_irq().
> 
> This patch simply re-orders things, stopping all tasks before zero-ing the
> irq values, thereby avoiding the possibility of the race.
> 
> Signed-off-by: Paul Durrant <pdurrant@...zon.com>

Acked-by: Wei Liu <wei.liu@...nel.org>