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Date: Sat, 21 Nov 2020 08:00:00 +0100
From: Jann Horn <jannh@...gle.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: James Morris <jmorris@...ei.org>, "Serge E . Hallyn" <serge@...lyn.com>,
Al Viro <viro@...iv.linux.org.uk>, Andy Lutomirski <luto@...capital.net>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>, Arnd Bergmann <arnd@...db.de>,
Casey Schaufler <casey@...aufler-ca.com>, Jeff Dike <jdike@...toit.com>,
Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>,
Michael Kerrisk <mtk.manpages@...il.com>, Richard Weinberger <richard@....at>, Shuah Khan <shuah@...nel.org>,
Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>,
kernel list <linux-kernel@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>,
linux-security-module <linux-security-module@...r.kernel.org>,
"the arch/x86 maintainers" <x86@...nel.org>, Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v24 01/12] landlock: Add object management
On Thu, Nov 12, 2020 at 9:51 PM Mickaël Salaün <mic@...ikod.net> wrote:
> A Landlock object enables to identify a kernel object (e.g. an inode).
> A Landlock rule is a set of access rights allowed on an object. Rules
> are grouped in rulesets that may be tied to a set of processes (i.e.
> subjects) to enforce a scoped access-control (i.e. a domain).
>
> Because Landlock's goal is to empower any process (especially
> unprivileged ones) to sandbox themselves, we cannot rely on a
> system-wide object identification such as file extended attributes.
> Indeed, we need innocuous, composable and modular access-controls.
>
> The main challenge with these constraints is to identify kernel objects
> while this identification is useful (i.e. when a security policy makes
> use of this object). But this identification data should be freed once
> no policy is using it. This ephemeral tagging should not and may not be
> written in the filesystem. We then need to manage the lifetime of a
> rule according to the lifetime of its objects. To avoid a global lock,
> this implementation make use of RCU and counters to safely reference
> objects.
>
> A following commit uses this generic object management for inodes.
>
> Cc: James Morris <jmorris@...ei.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Serge E. Hallyn <serge@...lyn.com>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Reviewed-by: Jann Horn <jannh@...gle.com>
Still looks good, except for one comment:
[...]
> + /**
> + * @lock: Guards against concurrent modifications. This lock might be
> + * held from the time @usage drops to zero until any weak references
> + * from @underobj to this object have been cleaned up.
> + *
> + * Lock ordering: inode->i_lock nests inside this.
> + */
> + spinlock_t lock;
Why did you change this to "might be held" (v22 had "must")? Is the
"might" a typo?
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