From: Maciej S. Szmigiero mail@maciej.szmigiero.name

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: c26fd69fa009 ("X.509: Add a crypto key parser for binary (DER) X.509 certificates") Cc: stable@vger.kernel.org Signed-off-by: David Howells dhowells@redhat.com ---

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 7d81e6bb461a..b6cabac4b62b 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") == 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;