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 <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>
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@ -249,6 +249,15 @@ int x509_note_signature(void *context, size_t hdrlen,
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return -EINVAL;
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}
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if (strcmp(ctx->cert->sig->pkey_algo, "rsa") == 0) {
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/* Discard the BIT STRING metadata */
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if (vlen < 1 || *(const u8 *)value != 0)
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return -EBADMSG;
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value++;
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vlen--;
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}
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ctx->cert->raw_sig = value;
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ctx->cert->raw_sig_size = vlen;
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return 0;
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