Fix issue discovered by honggfuzzGptHeader::header_size is supposed to between, inclusive, 92 and the logical block size.Slice indexing goes out of range and panics if this isn't checked.Also check that it's enough for our GptHeader struct.

Author: DianaNites

Diff for: src/gpt.rs

@@ -78,6 +78,13 @@ fn check_validity<RS: Read + Seek>(
     block_size: u64,
 ) -> Result<(), InnerError> {
     ensure!(header.signature == EFI_PART, Signature);
+    ensure!(header.header_size >= 92, InvalidGptHeader);
+    // FIXME: This one shouldn't be a requirement.
+    ensure!(
+        header.header_size <= std::mem::size_of::<GptHeader>() as u32,
+        InvalidGptHeader
+    );
+    ensure!(header.header_size <= block_size as u32, InvalidGptHeader);
     let old_crc = std::mem::replace(&mut header.header_crc32, 0);
     let crc = calculate_crc(header);
     header.header_crc32 = old_crc;