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]
Message-Id: <200811221247.44558.knikanth@suse.de>
Date:	Sat, 22 Nov 2008 12:47:44 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, Fabio Checconi <fchecconi@...il.com>
Subject: Re: [PATCH] Exiting queue and task might race to free cic

Hi Jens

On Thursday 20 November 2008 10:27:06 Nikanth Karthikesan wrote:
> On Wednesday 19 November 2008 19:45:31 Jens Axboe wrote:
> > On Wed, Nov 19 2008, Nikanth Karthikesan wrote:
> >
> > Not sure this is enough, we probably need to copy the key to ensure that
> > we get a fresh value. How does this look?
>
> Agreed. Read barrier required. But the compiler hint, "likely" can stay?
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 6a062ee..4504b94 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -1318,7 +1318,15 @@ static void cfq_exit_single_io_context(struct
> io_context *ioc,
>  		unsigned long flags;
>
>  		spin_lock_irqsave(q->queue_lock, flags);
> -		__cfq_exit_single_io_context(cfqd, cic);
> +
> +		/*
> +		 * Ensure we get a fresh copy of the ->key to prevent
> +		 * race between exiting task and queue
> +		 */
> +		smp_read_barrier_depends();
> +		if (likely(cic->key))
> +			__cfq_exit_single_io_context(cfqd, cic);
> +
>  		spin_unlock_irqrestore(q->queue_lock, flags);
>  	}
>  }
>
> > Did you actually trigger this, or is it just from code inspection?
>
> No. But I am looking at another bug report on Suse Kernel where the bug is
> triggered during reboot when the kernel thread usb_stor_scan_thread exits.
>

This patch seems to solve the above said bug report on Suse kernel. So, yes it 
is reproducible! Can this be merged?

Thanks
Nikanth

--
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/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ