linux-kernel - [PATCH v4 5/6] KEYS: CA link restriction

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Date:   Mon,  6 Feb 2023 21:59:57 -0500
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     jarkko@...nel.org, zohar@...ux.ibm.com, dhowells@...hat.com,
        dwmw2@...radead.org
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, pvorel@...e.cz, tadeusz.struk@...el.com,
        eric.snowberg@...cle.com, kanth.ghatraju@...cle.com,
        konrad.wilk@...cle.com, erpalmer@...ux.vnet.ibm.com,
        coxu@...hat.com, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: [PATCH v4 5/6] KEYS: CA link restriction

Add a new link restriction.  Restrict the addition of keys in a keyring
based on the key to be added being a CA.

Signed-off-by: Eric Snowberg <eric.snowberg@...cle.com>
---
 crypto/asymmetric_keys/restrict.c | 38 +++++++++++++++++++++++++++++++
 include/crypto/public_key.h       | 15 ++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 6b1ac5f5896a..48457c6f33f9 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,44 @@ int restrict_link_by_signature(struct key *dest_keyring,
 	return ret;
 }
 
+/**
+ * restrict_link_by_ca - Restrict additions to a ring of CA keys
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @trust_keyring: Unused.
+ *
+ * Check if the new certificate is a CA. If it is a CA, then mark the new
+ * certificate as being ok to link.
+ *
+ * Returns 0 if the new certificate was accepted, -ENOKEY if the
+ * certificate is not a CA. -ENOPKG if the signature uses unsupported
+ * crypto, or some other error if there is a matching certificate but
+ * the signature check cannot be performed.
+ */
+int restrict_link_by_ca(struct key *dest_keyring,
+			const struct key_type *type,
+			const union key_payload *payload,
+			struct key *trust_keyring)
+{
+	const struct public_key *pkey;
+
+	if (type != &key_type_asymmetric)
+		return -EOPNOTSUPP;
+
+	pkey = payload->data[asym_crypto];
+	if (!pkey)
+		return -ENOPKG;
+	if (!test_bit(KEY_EFLAG_CA, &pkey->key_eflags))
+		return -ENOKEY;
+	if (!test_bit(KEY_EFLAG_KEYCERTSIGN, &pkey->key_eflags))
+		return -ENOKEY;
+	if (test_bit(KEY_EFLAG_DIGITALSIG, &pkey->key_eflags))
+		return -ENOKEY;
+
+	return 0;
+}
+
 static bool match_either_id(const struct asymmetric_key_id **pair,
 			    const struct asymmetric_key_id *single)
 {
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 03c3fb990d59..653992a6e941 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -75,6 +75,21 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
 						 const union key_payload *payload,
 						 struct key *trusted);
 
+#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
+extern int restrict_link_by_ca(struct key *dest_keyring,
+			       const struct key_type *type,
+			       const union key_payload *payload,
+			       struct key *trust_keyring);
+#else
+static inline int restrict_link_by_ca(struct key *dest_keyring,
+				      const struct key_type *type,
+				      const union key_payload *payload,
+				      struct key *trust_keyring)
+{
+	return 0;
+}
+#endif
+
 extern int query_asymmetric_key(const struct kernel_pkey_params *,
 				struct kernel_pkey_query *);
 
-- 
2.27.0