On Thu, Nov 12, 2020 at 9:51 PM Mickaël Salaün <mic@xxxxxxxxxxx> 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@xxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: Serge E. Hallyn <serge@xxxxxxxxxx> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> 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?
