linux-kernel - Re: [PATCH v30 02/12] landlock: Add ruleset and domain management

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Message-ID: <202103191114.C87C5E2B69@keescook>
Date:   Fri, 19 Mar 2021 11:40:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        David Howells <dhowells@...hat.com>,
        Jeff Dike <jdike@...toit.com>,
        Jonathan Corbet <corbet@....net>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Richard Weinberger <richard@....at>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        linux-security-module@...r.kernel.org, x86@...nel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v30 02/12] landlock: Add ruleset and domain management

On Tue, Mar 16, 2021 at 09:42:42PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@...ux.microsoft.com>
> 
> A Landlock ruleset is mainly a red-black tree with Landlock rules as
> nodes.  This enables quick update and lookup to match a requested
> access, e.g. to a file.  A ruleset is usable through a dedicated file
> descriptor (cf. following commit implementing syscalls) which enables a
> process to create and populate a ruleset with new rules.
> 
> A domain is a ruleset tied to a set of processes.  This group of rules
> defines the security policy enforced on these processes and their future
> children.  A domain can transition to a new domain which is the
> intersection of all its constraints and those of a ruleset provided by
> the current process.  This modification only impact the current process.
> This means that a process can only gain more constraints (i.e. lose
> accesses) over time.
> 
> Cc: James Morris <jmorris@...ei.org>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Acked-by: Serge Hallyn <serge@...lyn.com>
> Link: https://lore.kernel.org/r/20210316204252.427806-3-mic@digikod.net

(Aside: you appear to be self-adding your Link: tags -- AIUI, this is
normally done by whoever pulls your series. I've only seen Link: tags
added when needing to refer to something else not included in the
series.)

> [...]
> +static void put_rule(struct landlock_rule *const rule)
> +{
> +	might_sleep();
> +	if (!rule)
> +		return;
> +	landlock_put_object(rule->object);
> +	kfree(rule);
> +}

I'd expect this to be named "release" rather than "put" since it doesn't
do any lifetime reference counting.

> +static void build_check_ruleset(void)
> +{
> +	const struct landlock_ruleset ruleset = {
> +		.num_rules = ~0,
> +		.num_layers = ~0,
> +	};
> +
> +	BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
> +	BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
> +}

This is checking that the largest possible stored value is correctly
within the LANDLOCK_MAX_* macro value?

> [...]

The locking all looks right, and given your test coverage and syzkaller
work, it's hard for me to think of ways to prove it out any better. :)

Reviewed-by: Kees Cook <keescook@...omium.org>


-- 
Kees Cook