Re: [PATCH nf 1/1] netfilter: xt_IDLETIMER: scope timer reuse to the owning netns

[Florian Westphal <fw@strlen.de>]

Ren Wei <n05ec@lzu.edu.cn> wrote:
> From: Haoze Xie <royenheart@gmail.com>
> 
> IDLETIMER keeps timers in a module-global list and reuses them
> solely by label text.
> 
> The existing rev0 ALARM guard avoids the panic when rev0 reuses
> a rev1 ALARM timer from another netns, but it still lets same
> labels in different netns share the same timer object and the
> same sysfs entry.

Isn't that by design?

> Track the owning netns in struct idletimer_tg and only reuse
> timers when both the label and netns match. For non-init_net
> timers, derive a namespace-scoped sysfs name from the netns
> inode so non-init namespaces no longer collide in the global
> xt_idletimer sysfs directory.

How can that work?  How would userspace daemon relize that the
name has changed?

> This keeps init_net sysfs paths unchanged for ABI compatibility
> and preserves same-netns label reuse, while preventing the
> cross-netns timer-object aliasing that caused refcount, expiry,
> and teardown interference.

I don't think there is a bug here.  Two netns using same
files having same sysfs mount should naturally "conflict".

Maybe one could make a patch to force-detach an idletime
in a non-init userns if init userns asks for "foo" that
is already claimed by different userns (to avoid the "Dos"
angle).

But I'm not sure its worth it.