net: vlan: fix underflow for the real_dev refcnt

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@nvidia.com>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Link: https://lore.kernel.org/r/20211126015942.2918542-1-william.xuanziyang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index a3a0a5e994f5aeae550404701e72253a7e38a991..abaa5d96ded2453c2fb9b44d46e4146a965c9518 100644 (file)
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -184,9 +184,6 @@ 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 ab6dee28536daaaf825dfc22120ca111c6197f4b..a54535cbcf4cf55b81dcd955bf6e2baf79cd755e 100644 (file)
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -615,6 +615,9 @@ 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;
 }