Re: [PATCH net-next 1/3] net: ipvlan: fix potential UAF problem for phy_dev

On Mon, Mar 14, 2022 at 3:54 AM Ziyang Xuan
[off-list ref] wrote:

quoted

Add the reference operation to phy_dev of ipvlan to avoid
the potential UAF problem under the following known scenario:

Someone module puts the NETDEV_UNREGISTER event handler to a
work, and phy_dev is accessed in the work handler. But when
the work is excuted, phy_dev has been destroyed because upper
ipvlan did not get reference to phy_dev correctly.

Can you name the module deferring NETDEV_UNREGISTER to a work queue ?

The one I know is nb_netdevice netdevice notifier of roce_gid_mgmt.
It will trigger vlan's real_dev UAF. It is a syzbot problem.
See details:
https://syzkaller.appspot.com/bug?extid=e4df4e1389e28972e955

This sounds like a bug to me.

quoted

That likes as the scenario occurred by
commit 563bcbae3ba2 ("net: vlan: fix a UAF in vlan_dev_real_dev()").

Mentioning a commit that added a bug and many other commits trying to
fix it is a bit unfortunate.

Yes, I am sorry for that. I will keep improving the quality of my code.

The related problems have solved by the series patches of
commit faab39f63c1f ("net: allow out-of-order netdev unregistration").
So I think it is the right time to fix other modules' potential problem.

Can you instead add a Fixes: tag ?

The potential problem exists since macvlan and ipvlan were added.

Do you have a repro to trigger the bug ?

For macvlan and ipvlan, there are not repros now. I think it is necessary
to give a right logic to cope with the constant evolution of the kernel.

quoted

Signed-off-by: Ziyang Xuan <redacted>
---
 drivers/net/ipvlan/ipvlan_main.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c
index 696e245f6d00..dcdc01403f22 100644
--- a/drivers/net/ipvlan/ipvlan_main.c
+++ b/drivers/net/ipvlan/ipvlan_main.c

@@ -158,6 +158,10 @@ static int ipvlan_init(struct net_device *dev)
        }
        port = ipvlan_port_get_rtnl(phy_dev);
        port->count += 1;
+
+       /* Get ipvlan's reference to phy_dev */
+       dev_hold(phy_dev);
+
        return 0;
 }

@@ -665,6 +669,14 @@ void ipvlan_link_delete(struct net_device *dev, struct list_head *head)
 }
 EXPORT_SYMBOL_GPL(ipvlan_link_delete);

+static void ipvlan_dev_free(struct net_device *dev)
+{
+       struct ipvl_dev *ipvlan = netdev_priv(dev);
+
+       /* Get rid of the ipvlan's reference to phy_dev */
+       dev_put(ipvlan->phy_dev);
+}
+
 void ipvlan_link_setup(struct net_device *dev)
 {
        ether_setup(dev);

@@ -674,6 +686,7 @@ void ipvlan_link_setup(struct net_device *dev)
        dev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
        dev->netdev_ops = &ipvlan_netdev_ops;
        dev->needs_free_netdev = true;
+       dev->priv_destructor = ipvlan_dev_free;
        dev->header_ops = &ipvlan_header_ops;
        dev->ethtool_ops = &ipvlan_ethtool_ops;
 }
--

2.25.1

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