security: Add hooks to rule on setting a watch

Add security hooks that will allow an LSM to rule on whether or not a watch
may be set.  More than one hook is required as the watches watch different
types of object.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jamorris@linux.microsoft.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
cc: Stephen Smalley <sds@tycho.nsa.gov>
cc: linux-security-module@vger.kernel.org
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 0b5e576..3f1374c 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1446,6 +1446,11 @@
  *	@cred: The event-triggerer's credentials
  *	@n: The notification being posted
  *
+ * @watch_key:
+ *	Check to see if a process is allowed to watch for event notifications
+ *	from a key or keyring.
+ *	@key: The key to watch.
+ *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
  *