linux-kernel - Re: [PATCH 2/2] exec: allow core_pipe recursion check to look for a value of 1 rather than 0 (v2)

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Message-ID: <20100131160030.GB1950@localhost.localdomain>
Date:	Sun, 31 Jan 2010 12:41:48 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jmoskovc@...hat.com, mingo@...hat.com, drbd-dev@...ts.linbit.com,
	benh@...nel.crashing.org, t.sailer@...mni.ethz.ch, abelay@....edu,
	gregkh@...e.de, spock@...too.org, viro@...iv.linux.org.uk,
	neilb@...e.de, mfasheh@...e.com, menage@...gle.com,
	shemminger@...ux-foundation.org, takedakn@...data.co.jp
Subject: Re: [PATCH 2/2] exec: allow core_pipe recursion check to look for a
 value of 1 rather than 0 (v2)

On Sun, Jan 31, 2010 at 04:50:01PM +0100, Oleg Nesterov wrote:
> On 01/29, Neil Horman wrote:
> >
> >  void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> >  {
> > ...
> > -		if (call_usermodehelper_pipe(helper_argv[0], helper_argv, NULL,
> > -				&cprm.file)) {
> > +		cprm.file = NULL;
> 
> it is already NULL,
> 
Are we sure, it was declared on the stack.  I think its safer to ensure that its
NULL.
 
> > +		if (call_usermodehelper_fns(helper_argv[0], helper_argv, NULL,
> > +					    UMH_WAIT_EXEC, umh_pipe_setup,
> > +					    NULL, &cprm)) {
> > +			if (cprm.file)
> > +				filp_close(cprm.file, NULL);
> 
> Hmm. Looks like this change fixes the bug by accident.
> 
> Before this patch, I think we leak info->stdin if kernel_thread() fails
> in __call_usermodehelper() pathes.
> 
I think we did that in call_usermodehelper_pipe.

> 
> 
> Completely off-topic, but I think __call_usermodehelper(UMH_NO_WAIT) is
> buggy. if kernel_thread() failes it should do call_usermodehelper_freeinfo().
> Also, UMH_WAIT_EXEC should set ->retval in this case.
> 
I went down that path last time I changed this code, Andrew and I decided that
yes it was buggy, but someone (can't recall how) smacked me around a bit and
explained how it worked (some odd artifact behavior of the scheduler).  Its in
the lkml archives if you want to get the whole story.

> Cough. And why call_usermodehelper_exec() has this strange ->path[0] == '\0'
> check?
> 
That I can't explain.  I figured I'd let that sleeping dog lie until this got
striaghtened out and fix it separately if it needed it
Neil

> Oleg.
> 
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