This is a note to let you know that I've just added the patch titled net: vlan: fix underflow for the real_dev refcnt to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-vlan-fix-underflow-for-the-real_dev-refcnt.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 682ca560fcf34921a453347a0c4f07ea6a81399f Author: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx> Date: Fri Nov 26 09:59:42 2021 +0800 net: vlan: fix underflow for the real_dev refcnt [ Upstream commit 01d9cc2dea3fde3bad6d27f464eff463496e2b00 ] Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute the following testcase: ip link add dev dummy1 type dummy ip link add name dummy1.100 link dummy1 type vlan id 100 ip link del dev dummy1 When the dummy netdevice is removed, we will get a WARNING as following: ======================================================================= refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 and an endless loop of: ======================================================================= unregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824 That is because dev_put(real_dev) in vlan_dev_free() be called without dev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev underflow. Move the dev_hold(real_dev) to vlan_dev_init() which is the call-back of ndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev symmetrical. Fixes: 563bcbae3ba2 ("net: vlan: fix a UAF in vlan_dev_real_dev()") Reported-by: Petr Machata <petrm@xxxxxxxxxx> Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx> Link: https://lore.kernel.org/r/20211126015942.2918542-1-william.xuanziyang@xxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index ad3780067a7d8..d12c9a8a9953e 100644 --- a/net/8021q/vlan.c +++ b/net/8021q/vlan.c @@ -181,9 +181,6 @@ int register_vlan_dev(struct net_device *dev, struct netlink_ext_ack *extack) if (err) goto out_unregister_netdev; - /* Account for reference in struct vlan_dev_priv */ - dev_hold(real_dev); - vlan_stacked_transfer_operstate(real_dev, dev, vlan); linkwatch_fire_event(dev); /* _MUST_ call rfc2863_policy() */ diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c index c7eba7dab0938..86a1c99025ea0 100644 --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c @@ -606,6 +606,9 @@ static int vlan_dev_init(struct net_device *dev) if (!vlan->vlan_pcpu_stats) return -ENOMEM; + /* Get vlan's reference to real_dev */ + dev_hold(real_dev); + return 0; }