pe(certificate_table): reinforce checks when writing aligned attribut…

…e certificates

It's possible that a user may pass an improperly created attribute certificate
and the write will cause all sorts of failure.

We sprinkle some `debug_assert!` to avoid this.

src/pe/certificate_table.rs

@@ -177,10 +177,22 @@ impl<'a> ctx::TryIntoCtx<scroll::Endian> for &AttributeCertificate<'a> {
  /// Writes an aligned attribute certificate in the buffer.
  fn try_into_ctx(self, bytes: &mut [u8], ctx: scroll::Endian) -> Result<usize, Self::Error> {
  let offset = &mut 0;
+ debug_assert!(
+ (self.length - ATTRIBUTE_CERTIFICATE_HEADER_SIZEOF as u32) % 16 == 0,
+ "Attribute certificate's length field is unaligned"
+ );
+ debug_assert!(
+ bytes.len() >= self.length as usize,
+ "Insufficient buffer to write an aligned certificate"
+ );
  bytes.gwrite_with(self.length, offset, ctx)?;
  bytes.gwrite_with(self.revision as u16, offset, ctx)?;
  bytes.gwrite_with(self.certificate_type as u16, offset, ctx)?;
- // Extend by zero the buffer until it is aligned on a quadword (16 bytes).
+ // Extend by zero the buffer until it is aligned on a quadword (16 bytes), according to
+ // spec:
+ // > If the bCertificate content does not end on a quadword boundary, the attribute
+ // > certificate entry is padded with zeros, from the end of bCertificate to the next
+ // > quadword boundary.
  let maybe_certificate_padding = pad(self.certificate.len(), Some(16usize));
  bytes.gwrite(self.certificate, offset)?;
  if let Some(cert_padding) = maybe_certificate_padding {