crypto: enforce that key material doesn't overlap with LUKS header

We already check that key material doesn't overlap between key slots,
and that it doesn't overlap with the payload. We didn't check for
overlap with the LUKS header.

Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto/block-luks.c

@@ -595,6 +595,14 @@ qcrypto_block_luks_check_header(const QCryptoBlockLUKS *luks, Error **errp)
             return -1;
         }
 
+        if (start1 < DIV_ROUND_UP(sizeof(QCryptoBlockLUKSHeader),
+                                  QCRYPTO_BLOCK_LUKS_SECTOR_SIZE)) {
+            error_setg(errp,
+                       "Keyslot %zu is overlapping with the LUKS header",
+                       i);
+            return -1;
+        }
+
         if (start1 + len1 > luks->header.payload_offset_sector) {
             error_setg(errp,
                        "Keyslot %zu is overlapping with the encrypted payload",