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

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Message-ID: <20130307200722.GA22072@redhat.com>
Date:	Thu, 7 Mar 2013 21:07:22 +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

On 03/07, Lucas De Marchi wrote:
>
> On Thu, Mar 7, 2013 at 4:37 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> >> @@ -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.
>
> Even if it's killed, we would just free the resource we allocated
> before.

Yes, and after that ____call_usermodehelper() can do
do_execve(module_name) ?

> It would not be safe if we allocated in the init function and
> freed in the cleanup.

But we do? We free this memory in cleanup ? And I was allocated by us.

sub_info itself can't go away (if you meant this), but
sub_info->path/argv/envp can.

> Or am I missing something?

Or me...

Oleg.

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