linux-kernel - Re: [PATCH v3] lockdown,selinux: fix wrong subject in some SELinux lockdown checks

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Message-ID: <8735tdiyc1.ffs@nanos.tec.linutronix.de>
Date:   Sat, 19 Jun 2021 19:00:30 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ondrej Mosnacek <omosnace@...hat.com>,
        linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        selinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        x86@...nel.org, linux-acpi@...r.kernel.org,
        linux-cxl@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-serial@...r.kernel.org,
        bpf@...r.kernel.org, netdev@...r.kernel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v3] lockdown,selinux: fix wrong subject in some SELinux lockdown checks

On Wed, Jun 16 2021 at 10:51, Ondrej Mosnacek wrote:
> diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
> index bda73cb7a044..c43a13241ae8 100644
> --- a/arch/x86/mm/testmmiotrace.c
> +++ b/arch/x86/mm/testmmiotrace.c
> @@ -116,7 +116,7 @@ static void do_test_bulk_ioremapping(void)
>  static int __init init(void)
>  {
>  	unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
> -	int ret = security_locked_down(LOCKDOWN_MMIOTRACE);
> +	int ret = security_locked_down(current_cred(), LOCKDOWN_MMIOTRACE);

I have no real objection to those patches, but it strikes me odd that
out of the 62 changed places 58 have 'current_cred()' and 4 have NULL as
argument.

I can't see why this would ever end up with anything else than
current_cred() or NULL and NULL being the 'special' case. So why not
having security_locked_down_no_cred() and make current_cred() implicit
for security_locked_down() which avoids most of the churn and just makes
the special cases special. I might be missing something though.

Thanks,

        tglx