netdev - Re: [PATCH net] tun: properly test for IFF

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Date:   Fri, 15 Mar 2019 15:43:28 -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] tun: properly test for IFF_UP

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu, 14 Mar 2019 20:19:47 -0700

> Same reasons than the ones explained in commit 4179cb5a4c92
> ("vxlan: test dev->flags & IFF_UP before calling netif_rx()")
> 
> netif_rx_ni() or napi_gro_frags() 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 layer.
> 
> 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.
> 
> Fixes: 1bd4978a88ac ("tun: honor IFF_UP in tun_get_user()")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable, thanks Eric.