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

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Date:   Mon, 11 Feb 2019 12:44:54 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, petrm@...lanox.com,
        idosch@...lanox.com, roopa@...ulusnetworks.com, sbrivio@...hat.com
Subject: Re: [PATCH net] vxlan: test dev->flags & IFF_UP before calling
 netif_rx()

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu,  7 Feb 2019 12:27:38 -0800

> netif_rx() 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.
> 
> 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.
> 
> Note this patch also fixes a small issue that came
> with commit ce6502a8f957 ("vxlan: fix a use after free
> in vxlan_encap_bypass"), since the dev->stats.rx_dropped
> change was done on the wrong device.
> 
> Fixes: d342894c5d2f ("vxlan: virtual extensible lan")
> Fixes: ce6502a8f957 ("vxlan: fix a use after free in vxlan_encap_bypass")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable.