linux-kernel - Re: [PATCH] usermodehelper: kill the sub

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Message-ID: <CAKi4VAJfYJ1SJzBj7QwOOu9ZoKqvQUWefGyN8jKzDCTQ7AaqyA@mail.gmail.com>
Date:	Tue, 21 May 2013 22:09:57 -0300
From:	Lucas De Marchi <lucas.de.marchi@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usermodehelper: kill the sub_info->path[0] check

Hi Oleg,

On Mon, May 20, 2013 at 1:55 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> call_usermodehelper_exec() does nothing but returns success if
> path[0] == 0. The only user which needs this strange feature is
> request_module(), it can check modprobe_path[0] itself like other
> users do if they want to detect the "disabled by admin" case.
>
> Kill it. Not only it looks strange, it can confuse other callers.
> And this allows us to revert 264b83c0 "usermodehelper: check
> subprocess_info->path != NULL", do_execve(NULL) is safe.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-By: Lucas De Marchi <lucas.demarchi@...el.com>

But... see below.

> ---
>  kernel/kmod.c |   11 +++--------
>  1 files changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/kmod.c b/kernel/kmod.c
> index 8241906..fb32636 100644
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -147,6 +147,9 @@ int __request_module(bool wait, const char *fmt, ...)
>          */
>         WARN_ON_ONCE(wait && current_is_async());
>
> +       if (!modprobe_path[0])
> +               return 0;
> +

Any reason to not return -EINVAL here except for maintaining the
previous behavior? Checking the callers reveals just a few of them
actually check the return value and IMO this is no different than the
binary not existing and failing later on exec.

>         va_start(args, fmt);
>         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
>         va_end(args);
> @@ -569,14 +572,6 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
>         int retval = 0;
>
>         helper_lock();
> -       if (!sub_info->path) {
> -               retval = -EINVAL;
> -               goto out;
> -       }
> -
> -       if (sub_info->path[0] == '\0')
> -               goto out;
> -
>         if (!khelper_wq || usermodehelper_disabled) {
>                 retval = -EBUSY;
>                 goto out;
> --

Lucas De Marchi
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