netdev - Re: [Patch net] net: saving irq context for peernet2id()

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Message-ID: <CAM_iQpWD3WiX1ZX+3LJ8vbJc42K1jZcZ4-f6MO5kzZY-+Szkqw@mail.gmail.com>
Date:   Thu, 20 Oct 2016 11:29:11 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Elad Raz <e@...draz.com>, Paul Moore <paul@...l-moore.com>,
        Richard Guy Briggs <rgb@...hat.com>
Subject: Re: [Patch net] net: saving irq context for peernet2id()

On Thu, Oct 20, 2016 at 7:58 AM, Stephen Smalley <sds@...ho.nsa.gov> wrote:
> On 10/20/2016 02:52 AM, Cong Wang wrote:
>> A kernel warning inside __local_bh_enable_ip() was reported by people
>> running SELinux, this is caused due to some SELinux functions
>> (indirectly) call peernet2id() with IRQ disabled in process context,
>> when we re-enable BH with IRQ disabled kernel complains. Shut up this
>> warning by saving IRQ context in peernet2id(), BH is still implicitly
>> disabled.
>
> Not sure this suffices; kill_fasync() -> send_sigio() ->
> send_sigio_to_task() -> sigio_perm() -> security_file_send_sigiotask()
> -> selinux_file_send_sigiotask() -> ... -> audit_log() -> ... ->
> peernet2id()

Oh, this is a new one. kill_fasync() is called in IRQ handler, so we actually
do multicast in IRQ context.... It makes no sense, netlink multicast could
be very expensive if we have many listeners.

I am Cc'ing Richard who added that multicast in audit_log_end(). It seems
not easy to just move the multicast to a workqueue, since the skb is copied
from audit_buffer which is freed immediately after that, probably need another
queue like audit_skb_queue.