netdev - Re: [PATCH net] gro_cells: make sure device is up in gro_cells

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Message-Id: <20190310.110824.1204384723110020616.davem@davemloft.net>
Date:   Sun, 10 Mar 2019 11:08:24 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] gro_cells: make sure device is up in
 gro_cells_receive()

From: Eric Dumazet <edumazet@...gle.com>
Date: Sun, 10 Mar 2019 10:39:37 -0700

> We keep receiving syzbot reports [1] that show that tunnels do not play
> the rcu/IFF_UP rules properly.
> 
> At device dismantle phase, gro_cells_destroy() will be called
> only after a full rcu grace period is observed after IFF_UP
> has been cleared.
> 
> This means that IFF_UP needs to be tested before queueing packets
> into netif_rx() or gro_cells.
> 
> This patch implements the test in gro_cells_receive() because
> too many callers do not seem to bother enough.

Yeah, better to put a safety valve in a common place.

...
> Fixes: c9e6bc644e55 ("net: add gro_cells infrastructure")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
>  Note: The Fixes: tag is somewhat arbitrary, since callers had to
>  implement proper IFF_UP tests before calling netif_rx() anyway,
>  before gro_cells was introduced.

Right.

Applied, thanks Eric.