linux-kernel - Re: [PATCH] livepatch: fix race between enabled_store() and klp_unregister

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]

Message-ID: <20151201165703.GC14230@pathway.suse.cz>
Date:	Tue, 1 Dec 2015 17:57:03 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Li Bin <huawei.libin@...wei.com>, sjenning@...hat.com,
	jikos@...nel.org, vojtech@...e.com, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org, guohanjun@...wei.com,
	dingtianhong@...wei.com, xiexiuqi@...wei.com,
	zhouchengming1@...wei.com, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH] livepatch: fix race between enabled_store() and
 klp_unregister_patch()

On Tue 2015-12-01 15:28:19, Jiri Slaby wrote:
> On 12/01/2015, 03:13 PM, Petr Mladek wrote:
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -612,7 +612,19 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
> >  
> >  	patch = container_of(kobj, struct klp_patch, kobj);
> >  
> > -	mutex_lock(&klp_mutex);
> > +	/*
> > +	 * Avoid a deadlock with kobject_put(&patch->kobj) that is
> > +	 * called under klp_mutex. Bail out when the patch is not
> > +	 * longer registered.
> > +	 */
> > +	if (!mutex_trylock(&klp_mutex)) {
>
> This introduces false positives.
> Deleting/enabling/disabling/other_op_under_klp_mutex of an unrelated
> patch may now cause enabled_store to fail. Hence I don't like this
> approach at all.

Ah, there should have been

	while (!mutex_trylock(&klp_mutex)) {
		if (!klp_is_patch_registered(patch))
			return -EINVAL;
		/* Do not spin with trylock that bounce cache lines. */
		while (mutex_is_locked(&klp_mutex) &&
		       klp_is_patch_registered(patch))
			cond_resched();
	}

, so it should not produce false positives.

But I do not have a strong opinion about it.

Best Regards,
Petr
--
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/