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

Kees Cook
2021-03-19T18:41:03Z

On Tue, Mar 16, 2021 at 09:42:42PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@linux.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@namei.org>
> Cc: Jann Horn <jannh@google.com>
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
> Acked-by: Serge Hallyn <serge@hallyn.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@chromium.org>

--
Kees Cook