On 19/03/2021 19:40, Kees Cook wrote:

On Tue, Mar 16, 2021 at 09:42:42PM +0100, Mickaël Salaün wrote:

quoted

From: Mickaël Salaün <redacted>

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 <redacted>
Signed-off-by: Mickaël Salaün <redacted>
Acked-by: Serge Hallyn <serge@hallyn.com>
Link: https://lore.kernel.org/r/20210316204252.427806-3-mic@digikod.net (local)

(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.)

It is an insurance to not lose history. :)

quoted

[...]
+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.

It does decrement rule->object->usage .

quoted

+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?

Yes, there is builtin checks for all Landlock limits.

quoted

[...]

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. :)

Thanks!

Reviewed-by: Kees Cook <redacted>