On 21/11/2020 08:00, Jann Horn wrote: > 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? > Good catch, a typo indeed.
