[RFC 1/8] key: add l_key_search

Search for a key by type, keyring name, and description. Returns the
key ID or an error if not found.
---
 ell/ell.sym |  1 +
 ell/key.c   | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 ell/key.h   |  3 +++
 3 files changed, 50 insertions(+)

diff --git a/ell/ell.sym b/ell/ell.sym
index 6df9024..414b288 100644
--- a/ell/ell.sym
+++ b/ell/ell.sym
@@ -387,6 +387,7 @@ global:
 	l_key_decrypt;
 	l_key_sign;
 	l_key_verify;
+	l_key_search;
 	l_keyring_new;
 	l_keyring_restrict;
 	l_keyring_free;
diff --git a/ell/key.c b/ell/key.c
index 24374a5..5a82531 100644
--- a/ell/key.c
+++ b/ell/key.c
@@ -270,6 +270,26 @@ static long kernel_key_verify(int32_t serial,
 	return result >= 0 ? result : -errno;
 }
 
+static long kernel_key_request(const char *type, const char *description)
+{
+	long result;
+
+	result = syscall(__NR_request_key, type, description, NULL, 0);
+
+	return result >= 0 ? result : -errno;
+}
+
+static long kernel_key_search(int32_t keyring_id, const char *type,
+				const char *description)
+{
+	long result;
+
+	result = syscall(__NR_keyctl, KEYCTL_SEARCH, keyring_id, type,
+				description, 0);
+
+	return result >= 0 ? result : -errno;
+}
+
 static bool setup_internal_keyring(void)
 {
 	internal_keyring = kernel_add_key("keyring", "ell-internal", NULL, 0,
@@ -283,6 +303,32 @@ static bool setup_internal_keyring(void)
 	return true;
 }
 
+LIB_EXPORT int32_t l_key_search(enum l_key_type type, const char *keyring,
+					const char *description)
+{
+	long keyring_id;
+	long key_id;
+
+	if (unlikely((size_t)type >= L_ARRAY_SIZE(key_type_names)))
+		return -EINVAL;
+
+	if (unlikely(!keyring || !description))
+		return -EINVAL;
+
+	/* Find the ID of the keyring */
+	keyring_id = kernel_key_request("keyring", keyring);
+	if (keyring_id < 0)
+		return -ENOENT;
+
+	/* Search for the key by type/description */
+	key_id = kernel_key_search(keyring_id, key_type_names[type],
+					description);
+	if (key_id < 0)
+		return -ENOENT;
+
+	return key_id;
+}
+
 LIB_EXPORT struct l_key *l_key_new(enum l_key_type type, const void *payload,
 					size_t payload_length)
 {
diff --git a/ell/key.h b/ell/key.h
index 6897105..5fe8e00 100644
--- a/ell/key.h
+++ b/ell/key.h
@@ -62,6 +62,9 @@ enum l_key_cipher_type {
 struct l_key *l_key_new(enum l_key_type type, const void *payload,
 			size_t payload_length);
 
+int32_t l_key_search(enum l_key_type type, const char *keyring,
+					const char *description);
+
 void l_key_free(struct l_key *key);
 void l_key_free_norevoke(struct l_key *key);
 
-- 
2.34.3