[PATCH RFC 03/12] KEYS: CA link restriction

Eric Snowberg
2021-07-07T02:45:20Z

Restrict the addition of keys in a keyring based on the key to be
added being a CA (self-signed) or by being vouched for by a key in
either the built-in or the secondary trusted keyrings.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
certs/system_keyring.c | 18 ++++++++++
crypto/asymmetric_keys/restrict.c | 60 +++++++++++++++++++++++++++++++
include/crypto/public_key.h | 5 +++
include/keys/system_keyring.h | 14 ++++++++
4 files changed, 97 insertions(+)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index f02bc5832684..b4c82276bba5 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -73,6 +73,24 @@ int restrict_link_by_builtin_and_secondary_trusted(
secondary_trusted_keys);
}

+/**
+ * restrict_link_by_secondary_trusted_or_ca - Restrict keyring
+ * addition by being a CA or vouched by the secondary keyrings.
+ *
+ * Restrict the addition of keys in a keyring based on the key-to-be-added
+ * being a CA (self signed) or by being vouched for by a key in either
+ * the built-in or the secondary system keyrings.
+ */
+int restrict_link_by_secondary_trusted_or_ca(
+ struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *restrict_key)
+{
+ return restrict_link_by_ca(dest_keyring, type, payload,
+ secondary_trusted_keys);
+}
+
/**
* Allocate a struct key_restriction for the "builtin and secondary trust"
* keyring. Only for use in system_trusted_keyring_init().
diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 84cefe3b3585..75e4379226e8 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,66 @@ int restrict_link_by_signature(struct key *dest_keyring,
return ret;
}

+/**
+ * restrict_link_by_ca - Restrict additions to a ring of public keys
+ * based on it being a CA
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @trusted: A key or ring of keys that can be used to vouch for the new cert.
+ *
+ * Check if the new certificate is a CA or if they key can be vouched for
+ * by keys already linked in the destination keyring or the trusted
+ * keyring. If one of those is the signing key or it is self signed, then
+ * mark the new certificate as being ok to link.
+ *
+ * Returns 0 if the new certificate was accepted, -ENOKEY if we could not find
+ * a matching parent certificate in the trusted list. -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_signature *sig;
+ const struct public_key *pkey;
+ struct key *key;
+ int ret;
+
+ if (type != &key_type_asymmetric)
+ return -EOPNOTSUPP;
+
+ sig = payload->data[asym_auth];
+ if (!sig)
+ return -ENOPKG;
+
+ if (!sig->auth_ids[0] && !sig->auth_ids[1])
+ return -ENOKEY;
+
+ pkey = payload->data[asym_crypto];
+ if (!pkey)
+ return -ENOPKG;
+
+ ret = public_key_verify_signature(pkey, sig);
+ if (!ret)
+ return 0;
+
+ if (!trust_keyring)
+ return -ENOKEY;
+
+ key = find_asymmetric_key(trust_keyring,
+ sig->auth_ids[0], sig->auth_ids[1],
+ false);
+ if (IS_ERR(key))
+ return -ENOKEY;
+
+ ret = verify_signature(key, sig);
+ key_put(key);
+ return ret;
+}
+
static bool match_either_id(const struct asymmetric_key_ids *pair,
const struct asymmetric_key_id *single)
{
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 47accec68cb0..545af1ea57de 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -71,6 +71,11 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
const union key_payload *payload,
struct key *trusted);

+extern int restrict_link_by_ca(struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *trust_keyring);
+
extern int query_asymmetric_key(const struct kernel_pkey_params *,
struct kernel_pkey_query *);

diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index f40837026d6d..43c76fba9481 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -34,10 +34,24 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
const struct key_type *type,
const union key_payload *payload,
struct key *restriction_key);
+extern int restrict_link_by_secondary_trusted_or_ca(
+ struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *restrict_key);
extern __init int move_to_trusted_secondary_keyring(struct key *key,
struct key *from_keyring);
#else
#define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
+static inline int restrict_link_by_secondary_trusted_or_ca(
+ struct key *dest_keyring,
+ const struct key_type *type,
+ const union key_payload *payload,
+ struct key *restrict_key)
+{
+ return -ENOKEY;
+}
+
static inline __init int move_to_trusted_secondary_keyring(struct key *key,
struct key *from_keyring)
{
--
2.18.4