linux-kernel - Re: [PATCH 1/12] cpufreq: governor: Close dbs

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:	Fri, 19 Feb 2016 07:57:21 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/12] cpufreq: governor: Close dbs_data update race
 condition

On 18-02-16, 17:20, Rafael J. Wysocki wrote:
> On Thu, Feb 18, 2016 at 6:24 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 18-02-16, 02:19, Rafael J. Wysocki wrote:

> >> @@ -112,7 +112,7 @@ static ssize_t governor_store(struct kob
> >>
> >>       mutex_lock(&dbs_data->mutex);
> >>
> >> -     if (gattr->store)
> >> +     if (dbs_data->usage_count && gattr->store)
> >
> > That's not gonna be enough. The above lock doesn't guarantee
> > protection with any such races.

Oops, I completely misread it. Really sorry about that.

But now that I have read the code again, I wonder why we need this protection at
all. The first thing we do after decrementing the usage_count counter, is we put
the kobject. Which will ensure that the sysfs files are all gone. So, what is
the race we are trying to fix then?

> Yeah, they are quite useless.  But not in this patch.

Sure.

-- 
viresh