linux-kernel - Re: [PATCH] Module use count must be updated as bridges are created/destroyed

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-next>] [day] [month] [year] [list]

Date:	Thu, 27 Sep 2007 08:40:10 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Stephen Hemminger" <shemminger@...ux-foundation.org>
Cc:	<bridge@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Module use count must be updated as bridges are
	created/destroyed

>>> Stephen Hemminger <shemminger@...ux-foundation.org> 26.09.07 19:12 >>>
>On Wed, 26 Sep 2007 17:08:19 +0100
>"Jan Beulich" <jbeulich@...ell.com> wrote:
>
>> >>> Stephen Hemminger <shemminger@...ux-foundation.org> 26.09.07 17:37 >>>
>> >On Wed, 26 Sep 2007 08:53:27 +0100
>> >"Jan Beulich" <jbeulich@...ell.com> wrote:
>> >
>> >> Otherwise 'modprobe -r' on a module having a dependency on bridge will
>> >> implicitly unload bridge, bringing down all connectivity that was
>> >> using bridges.
>> >> 
>> >> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
>> >>
>> >
>> >No, network devices don't do reference counting.
>> >What is the dependency? Where is the source of the module interacting
>> >with the  bridge?
>> 
>> On a Xen system, I loaded and then unloaded ebtable_broute. The unload
>> implicitly unloaded bridge, destroying the network. The only way I could see
>> to avoid the implicit unload was to bump the reference count on bridge
>> creation. Otherwise I would have to ask why bridge has a zero reference
>> count despite a bridge being configured.
>> 
>> Jan
>
>Sounds like a module utilities problem since unloading one module doesn't
>normally unload others.

I have to disagree here - 'modprobe -r' is specifically unloading all modules the
specified one references as long as they have a use count of zero. The
difference to other networking modules is that the latter normally don't export
symbols, and hence don't have dependent modules (and thus cannot be
subject of implicit unloading). Bridge does have dependents, and hence must
avoid implicit unloading by managing its use count.

Jan

-
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/