On 10/22/15 at 05:00pm, Jiri Benc wrote: > On Thu, 22 Oct 2015 16:52:13 +0200, Nicolas Dichtel wrote: > > With the proposed scenario: > > 1. create netns 'new_netns' > > 2. in root netns, move the interface with ifindex 2 to new_netns > > 3. in new_netns, delete the interface with ifindex 2 > > 4. in new_netns, create an interface - it will get ifindex 2 > > > > Operation 2 and 4 are done by dev_change_net_namespace() under rtnl_lock(). > > RTM_DELLINK(root netns) and RTM_NEWLINK(new_netns) are sent by this > > function. > > It means that operation 3 has been done before and that > > RTM_DELLINK(new_netns) > > has been sent before. > > Imagine the application trying to configure the interface with ifindex 2 > after your step 2. It constructs a netlink message and sends it to the > kernel; but while doing so, steps 3 and 4 happen. Now the application > ends up configuring a different interface than it intended to. After > that, it polls the netlink socket and receives the notifications about > interface disappearing and a new one appearing. > > I don't see any way the user space application can prevent this. There > will always be a race between receiving netlink notifications and > sending config requests. > > I guess Thomas Haller can elaborate more as he ran into this.
I understand the race but when does it occur? Whoever creates the original interface owns it and is responsible for its lifecycle. *Iff* for some reason multiple entities manipulate the interface, then it's probably a lot safer to just use flock or something similar to serialize access entirely in user space. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
