• Maciej S. Szmigiero's avatar
    X.509: unpack RSA signatureValue field from BIT STRING · b65c32ec
    Maciej S. Szmigiero authored
    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: 's avatarMaciej S. Szmigiero <mail@maciej.szmigiero.name>
    Fixes: c26fd69f ("X.509: Add a crypto key parser for binary (DER) X.509 certificates")
    Cc: stable@vger.kernel.org
    Signed-off-by: 's avatarJames Morris <james.morris@microsoft.com>
    b65c32ec