linux-kernel - Re: [PATCH 2/3] lsm: introduce security_lsm_manage

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Message-ID: <CAPhsuW7q1hvOG7-uG2C8d_wWnOhEmvTmwnBcXZYVX-oJ8=5FJQ@mail.gmail.com>
Date: Tue, 6 May 2025 23:19:12 -0700
From: Song Liu <song@...nel.org>
To: Maxime Bélair <maxime.belair@...onical.com>
Cc: linux-security-module@...r.kernel.org, john.johansen@...onical.com, 
	paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com, mic@...ikod.net, 
	kees@...nel.org, stephen.smalley.work@...il.com, casey@...aufler-ca.com, 
	takedakn@...data.co.jp, penguin-kernel@...ove.sakura.ne.jp, 
	linux-api@...r.kernel.org, apparmor@...ts.ubuntu.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] lsm: introduce security_lsm_manage_policy hook

On Tue, May 6, 2025 at 7:40 AM Maxime Bélair
<maxime.belair@...onical.com> wrote:
>
> Define a new LSM hook security_lsm_manage_policy and wire it into the
> lsm_manage_policy() syscall so that LSMs can register a unified interface
> for policy management. This initial, minimal implementation only supports
> the LSM_POLICY_LOAD operation to limit changes.
>
> Signed-off-by: Maxime Bélair <maxime.belair@...onical.com>
[...]
> diff --git a/security/security.c b/security/security.c
> index fb57e8fddd91..256104e338b1 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5883,6 +5883,27 @@ int security_bdev_setintegrity(struct block_device *bdev,
>  }
>  EXPORT_SYMBOL(security_bdev_setintegrity);
>
> +/**
> + * security_lsm_manage_policy() - Manage the policies of LSMs
> + * @lsm_id: id of the lsm to target
> + * @op: Operation to perform (one of the LSM_POLICY_XXX values)
> + * @buf:  userspace pointer to policy data
> + * @size: size of @buf
> + * @flags: lsm policy management flags
> + *
> + * Manage the policies of a LSM. This notably allows to update them even when
> + * the lsmfs is unavailable is restricted. Currently, only LSM_POLICY_LOAD is
> + * supported.
> + *
> + * Return: Returns 0 on success, error on failure.
> + */
> +int security_lsm_manage_policy(u32 lsm_id, u32 op, void __user *buf,
> +                              size_t size, u32 flags)
> +{
> +       return call_int_hook(lsm_manage_policy, lsm_id, op, buf, size, flags);

If the LSM doesn't implement this hook, sys_lsm_manage_policy will return 0
for any inputs, right? This is gonna be so confusing for users.

Thanks,
Song