netdev - Re: [PATCH net] ppp: unlock all_ppp_mutex before registering device

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Date:   Mon, 15 Jan 2018 13:23:22 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     g.nault@...halink.fr
Cc:     netdev@...r.kernel.org, paulus@...ba.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH net] ppp: unlock all_ppp_mutex before registering device

From: Guillaume Nault <g.nault@...halink.fr>
Date: Wed, 10 Jan 2018 16:24:45 +0100

> ppp_dev_uninit(), which is the .ndo_uninit() handler of PPP devices,
> needs to lock pn->all_ppp_mutex. Therefore we mustn't call
> register_netdevice() with pn->all_ppp_mutex already locked, or we'd
> deadlock in case register_netdevice() fails and calls .ndo_uninit().
> 
> Fortunately, we can unlock pn->all_ppp_mutex before calling
> register_netdevice(). This lock protects pn->units_idr, which isn't
> used in the device registration process.
> 
> However, keeping pn->all_ppp_mutex locked during device registration
> did ensure that no device in transient state would be published in
> pn->units_idr. In practice, unlocking it before calling
> register_netdevice() doesn't change this property: ppp_unit_register()
> is called with 'ppp_mutex' locked and all searches done in
> pn->units_idr hold this lock too.
> 
> Fixes: 8cb775bc0a34 ("ppp: fix device unregistration upon netns deletion")
> Reported-and-tested-by: syzbot+367889b9c9e279219175@...kaller.appspotmail.com
> Signed-off-by: Guillaume Nault <g.nault@...halink.fr>

Applied and queued up for -stable, thank you.