ppp: unlock all_ppp_mutex before registering device
commit 0171c41835591e9aa2e384b703ef9a6ae367c610 upstream. 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@syzkaller.appspotmail.com Signed-off-by: Guillaume Nault <g.nault@alphalink.fr> Signed-off-by: David S. Miller <davem@davemloft.net> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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@ -2764,6 +2764,8 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
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ppp->file.index = unit;
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sprintf(dev->name, "ppp%d", unit);
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mutex_unlock(&pn->all_ppp_mutex);
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ret = register_netdevice(dev);
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if (ret != 0) {
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/* register_netdevice() may have called ppp_dev_init()
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@ -2772,6 +2774,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
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*/
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if (dev->qdisc_tx_busylock)
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ppp_dev_priv_destructor(dev);
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mutex_lock(&pn->all_ppp_mutex);
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unit_put(&pn->units_idr, unit);
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netdev_err(ppp->dev, "PPP: couldn't register device %s (%d)\n",
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dev->name, ret);
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@ -2779,7 +2782,6 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
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}
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atomic_inc(&ppp_unit_count);
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mutex_unlock(&pn->all_ppp_mutex);
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rtnl_unlock();
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*retp = 0;
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