On Wed, Aug 24, 2022 at 02:04:09PM -0500, Denis Kenzior wrote:
> 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; fix that.
Instead of "fix that" just describe the change.
> Fixes: 299f561a6693 ("x509: Add support for parsing x509 certs with ECDSA keys")
> Signed-off-by: Denis Kenzior <denkenz@xxxxxxxxx>
> ---
> 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
>
The code change lgtm.
BR, Jarkko
