When support for ECDSA keys was added, constraints for data & signature
sizes were never updated. This makes it impossible to use such keys via
keyctl API from userspace.
Update constraint on max_data_size to 64 bytes in order to support
SHA512-based signatures. Also update the signature length constraints
per ECDSA signature encoding described in RFC 5480.
Fixes: 299f561a6693 ("x509: Add support for parsing x509 certs with ECDSA keys")
Signed-off-by: Denis Kenzior <denkenz@xxxxxxxxx>
---
Version History:
v2: Update patch description according to Jarkko's comments. No
functional code changes.
crypto/asymmetric_keys/public_key.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index 2f8352e88860..eca5671ad3f2 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -186,8 +186,28 @@ static int software_key_query(const struct kernel_pkey_params *params,
len = crypto_akcipher_maxsize(tfm);
info->key_size = len * 8;
- info->max_data_size = len;
- info->max_sig_size = len;
+
+ if (strncmp(pkey->pkey_algo, "ecdsa", 5) == 0) {
+ /*
+ * ECDSA key sizes are much smaller than RSA, and thus could
+ * operate on (hashed) inputs that are larger than key size.
+ * For example SHA384-hashed input used with secp256r1
+ * based keys. Set max_data_size to be at least as large as
+ * the largest supported hash size (SHA512)
+ */
+ info->max_data_size = 64;
+
+ /*
+ * Verify takes ECDSA-Sig (described in RFC 5480) as input,
+ * which is actually 2 'key_size'-bit integers encoded in
+ * ASN.1. Account for the ASN.1 encoding overhead here.
+ */
+ info->max_sig_size = 2 * (len + 3) + 2;
+ } else {
+ info->max_data_size = len;
+ info->max_sig_size = len;
+ }
+
info->max_enc_size = len;
info->max_dec_size = len;
info->supported_ops = (KEYCTL_SUPPORTS_ENCRYPT |
--
2.35.1
