Le 22/10/2015 17:00, Jiri Benc a écrit :
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.
Understood.
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.
Yeah, I'm also starting to think that reducing this window is the way to go.
Thank you,
Nicolas
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