netdev - Re: [PATCH net v2] xen-netback: avoid race that can lead to NULL pointer dereference

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Message-ID: <20191215114139.34f0d24e@cakuba.netronome.com>
Date:   Sun, 15 Dec 2019 11:41:39 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Paul Durrant <pdurrant@...zon.com>
Cc:     <xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Juergen Gross <jgross@...e.com>,
        Wei Liu <wei.liu@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net v2] xen-netback: avoid race that can lead to NULL
 pointer dereference

On Fri, 13 Dec 2019 13:20:40 +0000, Paul Durrant wrote:
> 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.
> 
> Fixes: 2ac061ce97f4 ("xen/netback: cleanup init and deinit code")
> Signed-off-by: Paul Durrant <pdurrant@...zon.com>

> v2:
>  - Add 'Fixes' tag and re-work commit comment

I've added Wei's Ack from v1, if the code doesn't change substantially
please keep people's Acks.

Applied, thanks.