module: invoke kobject uevent before sending LIVE notification
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Message ID 20210113003310.GA3040@pi3.com.pl
State New, archived
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Series
  • module: invoke kobject uevent before sending LIVE notification
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Commit Message

Adam Zabrocki Jan. 13, 2021, 12:33 a.m. UTC
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.

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@pi3.com.pl>
---
 kernel/module.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Greg Kroah-Hartman Jan. 13, 2021, 7:44 a.m. UTC | #1
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@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@linuxfoundation.org>

Patch
diff mbox series

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);
-
        /*
         * We need to finish all async code before the module init sequence
         * is done.  This has potential to deadlock.  For example, a newly