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To: "Joshua Hudson" <joshudson@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: wait4/waitpid/waitid oddness
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From: ebiederm@xmission.com (Eric W. Biederman)
Date: Fri, 07 Apr 2006 13:19:41 -0600
In-Reply-To: <bda6d13a0604071158x33080de3ya8016dde59c2d97f@mail.gmail.com> (Joshua
 Hudson's message of "Fri, 7 Apr 2006 11:58:40 -0700")
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"Joshua Hudson" <joshudson@gmail.com> writes:

> On 4/7/06, Eric W. Biederman <ebiederm@xmission.com> wrote:
>> "Albert Cahalan" <acahalan@gmail.com> writes:
>>
>> > The kernel prohibits:
>> >
>> > 1. WNOHANG on waitpid/wait4
>>
>> Not 2.6.17-rc1, and not for a lot of earlier kernels.
>> At least not on ingress, and just skimming the code
>> I can't see any deeper checks that would prevent this.
>>
>> > 2. __WALL on waitid
>> >
>> > Why? I need both at once.
>>
>> Which kernel is failing, and how?
>
> LKNL 2.6.16.1 has this check. Haven't checked any others.

So what I see current in wait4 is:
> asmlinkage long sys_wait4(pid_t pid, int __user *stat_addr,
> 			  int options, struct rusage __user *ru)
> {
> 	long ret;
> 
> 	if (options & ~(WNOHANG|WUNTRACED|WCONTINUED|
> 			__WNOTHREAD|__WCLONE|__WALL))
> 		return -EINVAL;

This denies access if you use other flags but it should allow
__WALL and WNOHANG together.  I didn't see anything in do_wait,
that would prohibit this.

> 	ret = do_wait(pid, options | WEXITED, NULL, stat_addr, ru);
> 
> 	/* avoid REGPARM breakage on x86: */
> 	prevent_tail_call(ret);
> 	return ret;
> }

So where are you seeing the check in 2.6.16.1?

Eric