On Wed, Feb 02, 2022 at 10:15:24PM -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@xxxxxxxxxxxx>
> > ---
> > crypto/asymmetric_keys/public_key.c | 15 +++++++++++++--
> > 1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> > index 4fefb219bfdc..3ffbab07ed2a 100644
> > --- a/crypto/asymmetric_keys/public_key.c
> > +++ b/crypto/asymmetric_keys/public_key.c
> > @@ -143,8 +143,19 @@ 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 ||
> > + strncmp(alg_name, "ecdsa-", 6) == 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;
> I don't know about the data size but following my tests this is not enough
> for ECDSA signature size. In ECDSA case the r and s components of the
> signature are encode in asn.1, not 'raw'. So there are 2 bytes at the
> beginning for sequence identifier , 2 bytes asn.1 for the r component, 1
> additional 0-byte to make the r component always a positive number, then the
> r component, then 2 bytes asn.1 for the s component, 1 addition 0-byte to
> make the s component a positive number, then the s component. Phew.
>
> info->max_sig_size = 2 + (2 + 1 + len) * 2;
>
> so for NIST P384 it's: 2 + (2+1+48) * 2 = 104
>
> Then it works for me as well.
Well, another solution, without changing API, is that max_size() should
return bigger size (to fit encoded signature), but in that case keyctl
will think wrongly about key_size.
Just for reference, keyctl_pkey_params_get_2 check that needs to be
passed:
case KEYCTL_PKEY_VERIFY:
if (uparams.in_len > info.max_sig_size ||
uparams.out_len > info.max_data_size)
return -EINVAL;
So we can return arbitrarily big value, in theory.
Thanks,
>
>
> > + } 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 |
