Commit b65c32ec authored by Maciej S. Szmigiero's avatar Maciej S. Szmigiero Committed by James Morris
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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: default avatarMaciej S. Szmigiero <>
Fixes: c26fd69f

 ("X.509: Add a crypto key parser for binary (DER) X.509 certificates")
Signed-off-by: default avatarJames Morris <>
parent 7b4e8843
......@@ -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;
ctx->cert->raw_sig = value;
ctx->cert->raw_sig_size = vlen;
return 0;
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