linux-kernel - Re: possible circular locking dependency in ISDN PPP

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]

Date:	Thu, 22 Oct 2009 10:27:25 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	Tilman Schmidt <tilman@...p.cc>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	isdn4linux <isdn4linux@...tserv.isdn4linux.de>,
	Netdev <netdev@...r.kernel.org>,
	Karsten Keil <isdn@...ux-pingi.de>
Subject: Re: possible circular locking dependency in ISDN PPP

On Thu, Oct 22, 2009 at 12:24 AM, Tilman Schmidt <tilman@...p.cc> wrote:
> Thanks for your analysis. The patch you propose does indeed prevent the
> "circular locking dependency" message, with no noticeable ill effect.
>
> I cannot say why xmit_lock was taken around isdn_net_lp_busy() in the
> first place. The ISDN4Linux people would be the ones to comment on that.
> If none of them objects, I propose you add a Signed-off-by line to your
> patch and submit it to Karsten Keil, the ISDN maintainer, for inclusion.
> You can also add a "Tested-by: Tilman Schmidt <tilman@...p.cc>" line.
>

Sure, I'll prepare a patch and send to Karsten later, Thanks.

> Thanks,
> Tilman
>
> Am 19.10.2009 07:27 schrieb Xiaotian Feng:
>> So there's a circular locking dependency.. Looking into isdn_net_get_locked_lp()
> [...]
>> Why do we need to hold xmit_lock while using
>> isdn_net_lp_busy(nd->queue) ? Can following patch fix this bug?
>>
>> ---
>> diff --git a/drivers/isdn/i4l/isdn_net.h b/drivers/isdn/i4l/isdn_net.h
>> index 74032d0..7511f08 100644
>> --- a/drivers/isdn/i4l/isdn_net.h
>> +++ b/drivers/isdn/i4l/isdn_net.h
>> @@ -83,19 +83,19 @@ static __inline__ isdn_net_local *
>> isdn_net_get_locked_lp(isdn_net_dev *nd)
>>
>>         spin_lock_irqsave(&nd->queue_lock, flags);
>>         lp = nd->queue;         /* get lp on top of queue */
>> -       spin_lock(&nd->queue->xmit_lock);
>>         while (isdn_net_lp_busy(nd->queue)) {
>> -               spin_unlock(&nd->queue->xmit_lock);
>>                 nd->queue = nd->queue->next;
>>                 if (nd->queue == lp) { /* not found -- should never happen */
>>                         lp = NULL;
>>                         goto errout;
>>                 }
>> -               spin_lock(&nd->queue->xmit_lock);
>>         }
>>         lp = nd->queue;
>>         nd->queue = nd->queue->next;
>> +       spin_unlock_irqrestore(&nd->queue_lock, flags);
>> +       spin_lock(&lp->xmit_lock);
>>         local_bh_disable();
>> +       return lp;
>>  errout:
>>         spin_unlock_irqrestore(&nd->queue_lock, flags);
>>         return lp;
>>
>
> --
> Tilman Schmidt                    E-Mail: tilman@...p.cc
> Bonn, Germany
> Diese Nachricht besteht zu 100% aus wiederverwerteten Bits.
> Ungeöffnet mindestens haltbar bis: (siehe Rückseite)
>
>
--
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/