Re: [PATCH net v2] sctp: fix race on protocol/netns initialization

[David Miller <davem@davemloft.net>]

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Thu, 10 Sep 2015 17:31:15 -0300

> Consider sctp module is unloaded and is being requested because an user
> is creating a sctp socket.
> 
> During initialization, sctp will add the new protocol type and then
> initialize pernet subsys:
 ...
> The problem is that after those calls to sctp_v{4,6}_protosw_init(), it
> is possible for userspace to create SCTP sockets like if the module is
> already fully loaded. If that happens, one of the possible effects is
> that we will have readers for net->sctp.local_addr_list list earlier
> than expected and sctp_net_init() does not take precautions while
> dealing with that list, leading to a potential panic but not limited to
> that, as sctp_sock_init() will copy a bunch of blank/partially
> initialized values from net->sctp.
> 
> The race happens like this:
 ...
> Simply inverting the initialization order between
> register_pernet_subsys() and sctp_v4_protosw_init() is not possible
> because register_pernet_subsys() will create a control sctp socket, so
> the protocol must be already visible by then. Deferring the socket
> creation to a work-queue is not good specially because we loose the
> ability to handle its errors.
> 
> So, as suggested by Vlad, the fix is to split netns initialization in
> two moments: defaults and control socket, so that the defaults are
> already loaded by when we register the protocol, while control socket
> initialization is kept at the same moment it is today.
> 
> Fixes: 4db67e808640 ("sctp: Make the address lists per network namespace")
> Signed-off-by: Vlad Yasevich <vyasevich@gmail.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Applied and queued up for -stable, thanks.