linux-kernel - Re: Q: sys_futex() && timespec

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Date:	Mon, 28 Jun 2010 16:37:15 +0200
From:	Jakub Jelinek <jakub@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ulrich Drepper <drepper@...hat.com>,
	Darren Hart <dvhltc@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andreas Schwab <schwab@...hat.com>,
	Danny Feng <dfeng@...hat.com>, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: Q: sys_futex() && timespec_valid()

On Mon, Jun 28, 2010 at 03:58:25PM +0200, Oleg Nesterov wrote:
> Honestly, it looks a bit strange to me that you blame the correct code,

Whether that is correct or not is what is being disputed.

> and at the same time you ignore the test-case which hangs because the
> kernel returns -EFAULT saying that this is the caller's problem.

The userspace code reads the abstime->tv_nsec value, so if it wouldn't
be valid address, the code would already segfault.  And that's fine, POSIX
certainly allows that, reporting EFAULT isn't required.  Well, it doesn't
read abstime->tv_sec in the assembly version, so if you try hard, you can
avoid the segfault, yet get EFAULT from futex syscall by putting abstime
8 bytes before start of some page with previous page not mmapped.

	Jakub
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