Re: [RFC PATCH] KEYS: Double max_size to make keyctl pkey_verify work

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/2/22 17:38, Vitaly Chikunov wrote:
> On Thu, Feb 03, 2022 at 12:24:37AM +0300, Vitaly Chikunov wrote:
>> Stefan,
>>
>> On Wed, Feb 02, 2022 at 07:55:43AM -0500, Stefan Berger wrote:
>>> On 2/2/22 01:59, Vitaly Chikunov wrote:
>>>> Rarely used `keyctl pkey_verify' can verify raw signatures, but was
>>>> failing, because ECDSA/EC-RDSA signature sizes are twice key sizes which
>>>> does not pass in/out sizes check in keyctl_pkey_params_get_2.
>>>> This in turn because these values cannot be distinguished by a single
>>>> `max_size' callback return value.
>>>> Also, `keyctl pkey_query` displays incorrect `max_sig_size' about these
>>>> algorithms.
>>>>
>>>> Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
>>> How do you use pkey_query?
>>>
>>> $ keyctl padd asymmetric testkey %keyring:test < cert.der
>>> 385037223
>> It should be (for RSA key):
>>
>>    keyctl pkey_query 385037223 0 enc=pkcs1 hash=sha256
>>
>> `0` is placeholder for a password.
>>
>> For example, I generated keys with your eckey-testing/generate.sh, and
>> pkey_query after this patch is applied:
>>    
>>    # keyctl padd asymmetric "" @u < ecdsa-ca/ca.crt.der
>>    66509339
>>    # keyctl pkey_query 66509339 0 enc=x962 hash=sha256
>>    key_size=256
>>    max_data_size=64
>>    max_sig_size=64
>>    max_enc_size=32
>>    max_dec_size=32
> I just thought, we can also set these to 0 if encrypt/decrypt is not
> enabled. Currently, there is no way to detect that encrypt is not
> possible, except by extending that if (strcmp...), but if we going to
> have it, why not correct other info too?


Sounds good.

This here works for signature verification for ECDSA now. [max_data_size 
= len * 2 was not enough]

diff --git a/crypto/asymmetric_keys/public_key.c 
b/crypto/asymmetric_keys/public_key.c
index 4fefb219bfdc..9e47a825b418 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -143,8 +143,26 @@ 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 (strcmp(alg_name, "ecrdsa") == 0) {
+               /*
+                * For these algos sig size is twice key size.
+                * keyctl uses max_sig_size as minimum input size, and
+                * max_data_size as minimum output size for a signature.
+                */
+               info->max_data_size = len * 2;
+               info->max_sig_size = len * 2;
+       } else if (strncmp(alg_name, "ecdsa-", 6) == 0) {
+               /*
+                * ECDSA encodes the signature in ASN.1 sequence (2 bytes)
+                * with 2 bytes identifying each integer and 1 byte prefixed
+                * to each integer to make it a positive number.
+                */
+               info->max_sig_size = 2 + (2 + 1 + len) * 2;
+               info->max_data_size = 2 + (2 + 1 + len) * 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 |