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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