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

Mickaël Salaün
2021-03-19T19:03:52Z

On 19/03/2021 19:40, Kees Cook wrote:
> 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.)

It is an insurance to not lose history. :)

>
>> [...]
>> +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 .

>
>> +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.

>
>> [...]
>
> 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 <keescook@chromium.org>
>
>