Re: [RFC] make thread-safe iface resolution in libnfnetlink

[Pablo Neira Ayuso <pablo@netfilter.org>]

Eric Leblond wrote:
> Hi,
> 
> I've encountered some problems with libnfnetlink iface resolution on a
> system where some interfaces are getting up and down: NuFW which uses
> this feature has crashed during a down/up of an interfaces. One of
> the reason seems that nufw uses one thread is used for iface related
> event treatment and another thread is doing iface name resolution.
> 
> As the hash can be modified or read without any lock, I think the
> problem can be linked with this issue. I thus propose a patch that
> modifies the iface resolution subsystem to make it thread-safe.

Better do the locking in your application. You can define the lock in
NuFW and protect the calls to libnfnetlink's interface API. Adding this
locking to a library does not seem to me like the right thing, see that
other non-threaded clients will have to live with the overhead of this
lock that is completely useless for them. Of course, we can document
that the interface API is not thread-safe.

I'm rewriting libnfnetlink from scratch (libnfnetlink2?) considering
this and other existing issues. I think that we can have better a
thread-safe interface API soon. Stay tuned.

-- 
"Los honestos son inadaptados sociales" -- Les Luthiers