linux-kernel - Re: Bug: fio traps into kernel without exiting because futex has a deadloop

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: <1244712980.6691.84.camel@laptop>
Date:	Thu, 11 Jun 2009 11:36:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Darren Hart <dvhltc@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Bug: fio traps into kernel without exiting because futex has a
 deadloop

On Thu, 2009-06-11 at 16:33 +0800, Zhang, Yanmin wrote:
> On Thu, 2009-06-11 at 08:18 +0200, Peter Zijlstra wrote:
> > On Thu, 2009-06-11 at 07:55 +0200, Peter Zijlstra wrote:
> > > On Thu, 2009-06-11 at 11:08 +0800, Zhang, Yanmin wrote:
> > > > I investigate a fio hang issue. When I run fio multi-process
> > > > testing on many disks, fio traps into kernel and doesn't exit
> > > > (mostly hit once after runing sub test cases for hundreds of times).
> > > > 
> > > > Oprofile data shows kernel consumes time with some futex functions.
> > > > Command kill couldn't kill the process and machine reboot also hangs.
> > > > 
> > > > Eventually, I locate the root cause as a bug of futex. Kernel enters
> > > > a deadloop between 'retry' and 'goto retry' in function futex_wake_op.
> > > > By unknown reason (might be an issue of fio or glibc), parameter uaddr2
> > > > points to an area which is READONLY. So futex_atomic_op_inuser returns
> > > > -EFAULT when trying to changing the data at uaddr2, but later get_user
> > > > still succeeds becasue the area is READONLY. Then go back to retry.
> > > > 
> > > > I create a simple test case to trigger it, which just shmat an READONLY
> > > > area for address uaddr2.
> > > > 
> > > > It could be used as a DOS attack.
> > 
> > /me has morning juice and notices he sent the wrong commit...
> > 
> > commit 64d1304a64477629cb16b75491a77bafe6f86963
> > Author: Thomas Gleixner <tglx@...utronix.de>
> > Date:   Mon May 18 21:20:10 2009 +0200
> 2.6.30 includes the new commit. I did a quick testing with my simple
> test case and it traps into kernel without exiting.
> 
> The reason is I use flag FUTEX_PRIVATE_FLAG. So the fshared part in function
> get_futex_key should be deleted. That might hurt performance.

No reason to, the easiest fix would be to simply propagate that -EFAULT
to userspace and let them chew on it, there's really nothing you can do
with a RO mapping.

--
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/