Commit 0171c418 authored Jan 10, 2018 by Guillaume Nault Committed by David S. Miller Jan 15, 2018

ppp: unlock all_ppp_mutex before registering device



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: 8cb775bc ("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>

parent 66940f35

drivers/net/ppp/ppp_generic.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -1006,17 +1006,18 @@ static int ppp_unit_register(struct ppp *ppp, int unit, bool ifname_is_set)
		if (!ifname_is_set)
		snprintf(ppp->dev->name, IFNAMSIZ, "ppp%i", ppp->file.index);

		mutex_unlock(&pn->all_ppp_mutex);

		ret = register_netdevice(ppp->dev);
		if (ret < 0)
		goto err_unit;

		atomic_inc(&ppp_unit_count);

		mutex_unlock(&pn->all_ppp_mutex);

		return 0;

		err_unit:
		mutex_lock(&pn->all_ppp_mutex);
		unit_put(&pn->units_idr, ppp->file.index);
		err:
		mutex_unlock(&pn->all_ppp_mutex);