2018-03-06 19:15:11

by Maciej S. Szmigiero

Subject: [PATCH] X.509: unpack RSA signatureValue field from BIT STRING

The signatureValue field of a X.509 certificate is encoded as a BIT STRING.
For RSA signatures this BIT STRING is of so-called primitive subtype, which
contains a u8 prefix indicating a count of unused bits in the encoding.

We have to strip this prefix from signature data, just as we already do for
key data in x509_extract_key_data() function.

This wasn't noticed earlier because this prefix byte is zero for RSA key
sizes divisible by 8. Since BIT STRING is a big-endian encoding adding zero
prefixes has no bearing on its value.

The signature length, however was incorrect, which is a problem for RSA
implementations that need it to be exactly correct (like AMD CCP).

Signed-off-by: Maciej S. Szmigiero <[email protected]>
Fixes: c26fd69fa009 ("X.509: Add a crypto key parser for binary (DER) X.509 certificates")
Cc: [email protected]
---
This is a resend without changes of a patch that was previously
submitted in one series with CCP driver changes since this particular
patch should go through the security (rather than crypto) tree.

crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index ce2df8c9c583..88c26a4538ae 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -249,6 +249,15 @@ int x509_note_signature(void *context, size_t hdrlen,
return -EINVAL;
}

+ if (!strcmp(ctx->cert->sig->pkey_algo, "rsa")) {
+ /* Discard the BIT STRING metadata */
+ if (vlen < 1 || *(const u8 *)value != 0)
+ return -EBADMSG;
+
+ value++;
+ vlen--;
+ }
+
ctx->cert->raw_sig = value;
ctx->cert->raw_sig_size = vlen;
return 0;

2018-03-07 15:45:34

by David Howells

Subject: Re: [PATCH] X.509: unpack RSA signatureValue field from BIT STRING

Maciej S. Szmigiero <[email protected]> wrote:

> + if (!strcmp(ctx->cert->sig->pkey_algo, "rsa")) {

I'm going to change this to '== 0' rather than '!'.

David

2018-03-07 17:57:55

by Maciej S. Szmigiero

Subject: Re: [PATCH] X.509: unpack RSA signatureValue field from BIT STRING

On 07.03.2018 16:44, David Howells wrote:
> Maciej S. Szmigiero <[email protected]> wrote:
>
>> + if (!strcmp(ctx->cert->sig->pkey_algo, "rsa")) {
>
> I'm going to change this to '== 0' rather than '!'.

No problem.
> David
>

Thanks,
Maciej

2018-03-23 15:26:44

by Maciej S. Szmigiero

Subject: Re: [PATCH] X.509: unpack RSA signatureValue field from BIT STRING

On 07.03.2018 18:56, Maciej S. Szmigiero wrote:
> On 07.03.2018 16:44, David Howells wrote:
>> Maciej S. Szmigiero <[email protected]> wrote:
>>
>>> + if (!strcmp(ctx->cert->sig->pkey_algo, "rsa")) {
>>
>> I'm going to change this to '== 0' rather than '!'.
>
> No problem.

I cannot find this patch in any tree that I have looked at.
Are you going to pick it up later or am I not looking at the right
place?

Thanks,
Maciej