[RFC PATCH 4/6] keys: Add keyring_is_empty() for {fs,dm}-verity

[Jarkko Sakkinen]

fs-verity and dm-verity read assoc_array's nr_leaves_on_tree directly to
check whether a keyring is empty.

Add keyring_is_empty() and use it in the both callers.

Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
 drivers/md/dm-verity-verify-sig.c                      |  2 +-
 fs/verity/signature.c                                  |  2 +-
 include/linux/key.h                                    |  1 +
 security/keys/keyring.c                                | 10 ++++++++++
 .../selftests/dm-verity/test-dm-verity-keyring.sh      |  2 +-
 5 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c
index b2b55c41e2cb..2ccb71bfb3ca 100644
--- a/drivers/md/dm-verity-verify-sig.c
+++ b/drivers/md/dm-verity-verify-sig.c
@@ -153,7 +153,7 @@ int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
 	if (ret != -ENOKEY && ret != -EKEYREJECTED)
 		return ret;
 
-	if (dm_verity_keyring->keys.nr_leaves_on_tree &&
+	if (!keyring_is_empty(dm_verity_keyring) &&
 	    dm_verity_keyring->restrict_link)
 		ret = verify_pkcs7_signature(root_hash, root_hash_len,
 					     sig_data, sig_len,
diff --git a/fs/verity/signature.c b/fs/verity/signature.c
index 0302a4e506ec..890d33b9d812 100644
--- a/fs/verity/signature.c
+++ b/fs/verity/signature.c
@@ -67,7 +67,7 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
 		return 0;
 	}
 
-	if (fsverity_keyring->keys.nr_leaves_on_tree == 0) {
+	if (keyring_is_empty(fsverity_keyring)) {
 		/*
 		 * The ".fs-verity" keyring is empty, due to builtin signatures
 		 * being supported by the kernel but not actually being used.
diff --git a/include/linux/key.h b/include/linux/key.h
index 26139c3adf62..d82253b06c54 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -436,6 +436,7 @@ extern int restrict_link_reject(struct key *keyring,
 				struct key *restriction_key);
 
 extern int keyring_clear(struct key *keyring);
+bool keyring_is_empty(const struct key *keyring);
 
 extern key_ref_t keyring_search(key_ref_t keyring,
 				struct key_type *type,
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 9ccce0db0665..613d1db41611 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -443,6 +443,16 @@ static void keyring_destroy(struct key *keyring)
 	assoc_array_destroy(&keyring->keys, &keyring_assoc_array_ops);
 }
 
+/**
+ * keyring_is_empty - Check whether a keyring contains any links
+ * @keyring: The keyring to check.
+ */
+bool keyring_is_empty(const struct key *keyring)
+{
+	return READ_ONCE(keyring->keys.nr_leaves_on_tree) == 0;
+}
+EXPORT_SYMBOL(keyring_is_empty);
+
 /*
  * Describe a keyring for /proc.
  */
diff --git a/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh b/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh
index 1f9601ef22f8..792449d356cf 100755
--- a/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh
+++ b/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh
@@ -746,7 +746,7 @@ test_keyring_inactive_when_empty() {
     log_info "TEST: Verify dm-verity keyring is inactive when sealed empty"
 
     # When keyring_unsealed=0, the keyring is sealed immediately while empty
-    # This means it should NOT be used for verification (nr_leaves_on_tree=0)
+    # An empty keyring should NOT be used for verification.
 
     log_info "Keyring state (should be empty and sealed):"
     list_keyring_keys
-- 
2.47.3