This is a note to let you know that I've just added the patch titled

ppp: unlock all_ppp_mutex before registering device

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: ppp-unlock-all_ppp_mutex-before-registering-device.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Jan 28 17:37:09 CET 2018

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

From: Guillaume Nault g.nault@alphalink.fr

[ Upstream commit 0171c41835591e9aa2e384b703ef9a6ae367c610 ]

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: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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);

Patches currently in stable-queue which might be from g.nault@alphalink.fr are

queue-4.9/pppoe-take-needed_headroom-of-lower-device-into-account-on-xmit.patch queue-4.9/ppp-unlock-all_ppp_mutex-before-registering-device.patch