security: fix the key_permission LSM hook function type

Commit 8c0637e ("keys: Make the KEY_NEED_* perms an enum rather than
a mask") changed the type of the key_permission callback functions, but
didn't change the type of the hook, which trips indirect call checking with
Control-Flow Integrity (CFI). This change fixes the issue by changing the
hook type to match the functions.

Fixes: 8c0637e ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <jmorris@namei.org>

include/linux/lsm_hook_defs.h

@@ -360,7 +360,7 @@ LSM_HOOK(int, 0, key_alloc, struct key *key, const struct cred *cred,
 	 unsigned long flags)
 LSM_HOOK(void, LSM_RET_VOID, key_free, struct key *key)
 LSM_HOOK(int, 0, key_permission, key_ref_t key_ref, const struct cred *cred,
-	 unsigned perm)
+	 enum key_need_perm need_perm)
 LSM_HOOK(int, 0, key_getsecurity, struct key *key, char **_buffer)
 #endif /* CONFIG_KEYS */