linux-kernel - Re: [PATCH] usermodehelper: Fix -ENOMEM return logic

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Date:	Thu, 7 Mar 2013 20:37:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Cc:	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
	James Morris <james.l.morris@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] usermodehelper: Fix -ENOMEM return logic

Hi Lucas,

On 03/06, Lucas De Marchi wrote:
>
> On Mon, Feb 25, 2013 at 3:08 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > So, I hope you will send v2. I'd suggest to split the fixes. 1/3
> > should create/export the new helpers, and 2-3 fix should call_modprobe()
> > and call_usermodehelper_keys(). But this is up to you, I won't insist.
>
> I was implementing this today, but looking into call_modprobe(), it is
> never called with UMH_NO_WAIT.

wait == T means UMH_WAIT_PROC, so we can't simply rely on CLONE_VFORK.
But probably we can rely on sys_wait4.

However,

> @@ -98,12 +93,13 @@ static int call_modprobe(char *module_name, int wait)
>  	argv[3] = module_name;	/* check free_modprobe_argv() */
>  	argv[4] = NULL;
> 
> -	return call_usermodehelper_fns(modprobe_path, argv, envp,
> -		wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
> +	ret = call_usermodehelper(modprobe_path, argv, envp,
> +				  wait | UMH_KILLABLE);
> +	kfree(module_name);

Please note UMH_KILLABLE. call_usermodehelper() can be interrupted
and even UMH_WAIT_EXEC case is not safe. If call_modprobe() is killed
we can return while the workqueue thread still tries to clone/exec/etc.

Oleg.

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