linux-kernel - Re: [PATCH] module: invoke kobject uevent before sending LIVE notification

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Date:   Wed, 13 Jan 2021 08:44:47 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Adam Zabrocki <pi3@....com.pl>
Cc:     Jessica Yu <jeyu@...nel.org>,
        Nicolas Morey-Chaisemartin <nmoreychaisemartin@...e.com>,
        linux-kernel@...r.kernel.org, Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH] module: invoke kobject uevent before sending LIVE
 notification

On Wed, Jan 13, 2021 at 01:33:10AM +0100, Adam Zabrocki wrote:
> The recent change "module: delay kobject uevent until after module init
> call", while helping avoid a race between udev/systemd and the module
> loader, made it unnecessarily more difficult to monitor kernel module
> integrity by out-of-tree projects such as Linux Kernel Runtime Guard.

We don't support out-of-tree kernel code, sorry.

> Specifically, that change delayed the kobject uevent unnecessarily too far,
> to until after sending a MODULE_STATE_LIVE notification.  As the uevent
> modifies internal state of the KOBJ itself, this violated the assumption
> (non-guaranteed yet handy while we can maintain it) that the KOBJ remains
> consistent and can be integrity-checked as soon as the module is LIVE.
> 
> To make all of these projects happy at once, move the kobject KOBJ_ADD
> uevent to just before sending the MODULE_STATE_LIVE notification.
> 
> Fixes: 38dc717e9715 ("module: delay kobject uevent until after module init call")
> Signed-off-by: Adam Zabrocki <pi3@....com.pl>
> ---
>  kernel/module.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 4bf30e4b3eaa..7d56b1b07237 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3681,14 +3681,14 @@ static noinline int do_init_module(struct module *mod)
>                 dump_stack();
>         }
> 
> +       /* Delay uevent until module has finished its init routine */
> +       kobject_uevent(&mod->mkobj.kobj, KOBJ_ADD);
> +
>         /* Now it's a first class citizen! */
>         mod->state = MODULE_STATE_LIVE;
>         blocking_notifier_call_chain(&module_notify_list,
>                                      MODULE_STATE_LIVE, mod);
> 
> -       /* Delay uevent until module has finished its init routine */
> -       kobject_uevent(&mod->mkobj.kobj, KOBJ_ADD);
> -

No, the code is correct as-is, userspace should be told _after_ the
kernel itself has handled all of the needed housekeeping of the module
being added.

so consider this:

Nacked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>