Fix PE/COFF checksum calculation

Only count the cert_table header once when performing the calculation
and counting buffer sizes.

The problem entered because of a mismerge of multiple signature
support and "be1f3d8 Update the PE checksum field using the
somewhat-underdocumented algorithm, so that we match the Microsoft
implementation in our signature generation.".  Originally
image->cert_table held the full certificate table including the
Microsoft _WINH_CERTIFICATE header and image->sigbuf pointed to the
pkcs11 signature inside, so the two had to be checksummed separately.
After multiple signature support, image->sigbuf points to the full
certificate table because we now need the headers to decide where one
signature ends and the next begins, so the correct checksum only needs
to sum over the entire image->sigbuf.

Signed-off-by: Steve McIntyre <93sam@debian.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/src/image.c b/src/image.c
index 745191f..3ada37b 100644
--- a/src/image.c
+++ b/src/image.c
@@ -162,7 +162,6 @@
 {
 	bool is_signed = image->sigsize && image->sigbuf;
 	uint32_t checksum;
-	struct cert_table_header *cert_table = image->cert_table;
 
 	/* We carefully only include the signature data in the checksum (and
 	 * in the file length) if we're outputting the signature.  Otherwise,
@@ -180,16 +179,13 @@
 			(void *)(image->checksum + 1));
 
 	if (is_signed) {
-		checksum = csum_bytes(checksum,
-				cert_table, sizeof(*cert_table));
-
 		checksum = csum_bytes(checksum, image->sigbuf, image->sigsize);
 	}
 
 	checksum += image->data_size;
 
 	if (is_signed)
-		checksum += sizeof(*cert_table) + image->sigsize;
+		checksum += image->sigsize;
 
 	*(image->checksum) = cpu_to_le32(checksum);
 }