netdev - Re: [PATCH net] vxlan: test dev->flags & IFF_UP before calling gro_cells

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Message-Id: <20190310.110642.514976433703549809.davem@davemloft.net>
Date:   Sun, 10 Mar 2019 11:06:42 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] vxlan: test dev->flags & IFF_UP before calling
 gro_cells_receive()

From: Eric Dumazet <edumazet@...gle.com>
Date: Sun, 10 Mar 2019 10:36:40 -0700

> Same reasons than the ones explained in commit 4179cb5a4c92
> ("vxlan: test dev->flags & IFF_UP before calling netif_rx()")
> 
> netif_rx() or gro_cells_receive() must be called under a strict contract.
> 
> At device dismantle phase, core networking clears IFF_UP
> and flush_all_backlogs() is called after rcu grace period
> to make sure no incoming packet might be in a cpu backlog
> and still referencing the device.
> 
> A similar protocol is used for gro_cells infrastructure, as
> gro_cells_destroy() will be called only after a full rcu
> grace period is observed after IFF_UP has been cleared.
> 
> Most drivers call netif_rx() from their interrupt handler,
> and since the interrupts are disabled at device dismantle,
> netif_rx() does not have to check dev->flags & IFF_UP
> 
> Virtual drivers do not have this guarantee, and must
> therefore make the check themselves.
> 
> Otherwise we risk use-after-free and/or crashes.
> 
> Fixes: d342894c5d2f ("vxlan: virtual extensible lan")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable, thanks Eric.