From: Guillaume Nault <g.nault@alphalink.fr>
Date: Wed, 10 Jan 2018 16:24:45 +0100
Subject: ppp: unlock all_ppp_mutex before registering device
Git-commit: 0171c41835591e9aa2e384b703ef9a6ae367c610
Patch-mainline: v4.15-rc9
References: networking-stable-18_01_28
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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
drivers/net/ppp/ppp_generic.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -1002,17 +1002,18 @@ static int ppp_unit_register(struct ppp
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);