linux-kernel - Re: [PATCH 1/4] module: implement module_inhibit

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

Date:	Tue, 25 Sep 2007 08:18:10 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Jonathan Corbet <corbet@....net>
CC:	ebiederm@...ssion.com, cornelia.huck@...ibm.com, greg@...ah.com,
	stern@...land.harvard.edu, kay.sievers@...y.org,
	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au
Subject: Re: [PATCH 1/4] module: implement module_inhibit_unload()

Jonathan Corbet wrote:
> Hi, Tejun,
> 
> I was just looking over these changes...
> 
>> +	/* Don't proceed till inhibition is lifted. */
>> +	add_wait_queue(&module_unload_wait, &wait);
>> +	set_current_state(TASK_UNINTERRUPTIBLE);
>> +	if (atomic_read(&module_unload_inhibit_cnt))
>> +		schedule();
>> +	__set_current_state(TASK_RUNNING);
>> +	remove_wait_queue(&module_unload_wait, &wait);
>> +
>> +	mutex_lock(&module_mutex);
> 
> Maybe I'm missing something, but this looks racy to me.  There's no
> check after schedule() to see if module_unload_inhibit_cnt is really
> zero, and nothing to keep somebody else from slipping in and raising it
> again afterward.

The unloading can proceed once module_unload_inhibit_cnt reaches zero.
An unloading thread only has to care about inhibition put in effect
before unloading has started, so there's no need to check again.

> Given your description of this tool as a "sledgehammer," might it not be
> easier to just take and hold module_mutex for the duration of the unload
> block?

That would be easier but...

* It would serialize users of the sledgehammer.
* It would block loading modules (which is often more important than
unloading them) when things go south.

-- 
tejun
-
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/