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X.509: unpack RSA signatureValue field from BIT STRING

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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 <mail@maciej.szmigiero.name>
Fixes: c26fd69fa0 ("X.509: Add a crypto key parser for binary (DER) X.509 certificates")
Cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.morris@microsoft.com>
This commit is contained in:
Maciej S. Szmigiero 2018-05-19 14:23:54 +02:00 committed by James Morris
parent 7b4e88434c
commit b65c32ec5a
1 changed files with 9 additions and 0 deletions
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9
crypto/asymmetric_keys/x509_cert_parser.c
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@ -249,6 +249,15 @@ int x509_note_signature(void *context, size_t hdrlen,
return -EINVAL;
}
if (strcmp(ctx->cert->sig->pkey_algo, "rsa") == 0) {
/* 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;