linux-kernel - Re: [PULL] modules-next

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <87zjagv5rt.fsf@rustcorp.com.au>
Date:	Mon, 22 Dec 2014 11:51:10 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ionut Alexa <ionut.m.alexa@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PULL] modules-next

Linus Torvalds <torvalds@...ux-foundation.org> writes:
> On Thu, Dec 18, 2014 at 4:55 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>
>> The exciting thing here is the getting rid of stop_machine on module
>> removal.  This is possible by using a simple atomic_t for the counter,
>> rather than our fancy per-cpu counter: it turns out that no one is doing
>> a module increment per net packet, so the slowdown should be in the noise.
>
> Famous last words. It may not happen per-packet, but I see
> module_get() in various block drivers and in netfilter code etc, and
> some of them may be pretty bad.
>
> Let's see how it all works out.

Indeed.  The general pattern is "get on open/init"; get-on-every-use was
most useful combined with blocking rmmod, which we removed a few kernels
ago (because no one used it).

I did a random audit until I got bored, and I put a printk-on-module-get
in my kernels for a while, and none of my usecases flood my logs.  But
it's definitely a risk...

Cheers,
Rusty.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/