Raise EOF error when needed

Author: rhpvorderman

src/isal/igzip.py

@@ -270,8 +270,9 @@ def _gzip_header_end(data: bytes) -> int:
     if method != 8:
         raise BadGzipFile("Unknown compression method")
     pos = 10
-    failure = False
     if flags & FEXTRA:
+        if len(data) < pos + 2:
+            raise eof_error
         xlen = int.from_bytes(data[pos: pos + 2], "little", signed=False)
         pos += 2 + xlen
     if flags & FNAME:
@@ -286,15 +287,15 @@ def _gzip_header_end(data: bytes) -> int:
             raise eof_error
         pos = fcomment_end
     if flags & FHCRC:
+        if len(data) < pos + 2:
+            raise eof_error
         header_crc = int.from_bytes(data[pos: pos + 2], "little", signed=False)
         # CRC is stored as a 16-bit integer by taking last bits of crc32.
         crc = isal_zlib.crc32(data[:pos]) & 0xFFFF
         if header_crc != crc:
             raise BadGzipFile(f"Corrupted header. Checksums do not "
                               f"match: {crc} != {header_crc}")
         pos += 2
-    if failure or pos > len(data):
-        raise eof_error
     return pos
 
 

tests/test_igzip.py

@@ -272,3 +272,19 @@ def test_header_corrupt():
         igzip.decompress(compressed)
     error.match(f"Corrupted header. "
                 f"Checksums do not match: {true_crc} != {crc}")
+
+
+TRUNCATED_HEADERS = [
+    b"\x1f\x8b\x08\x00\x00\x00\x00\x00\x00",  # Missing OS byte
+    b"\x1f\x8b\x08\x02\x00\x00\x00\x00\x00\xff",  # FHRC, but no checksum
+    b"\x1f\x8b\x08\x04\x00\x00\x00\x00\x00\xff",  # FEXTRA, but no xlen
+    b"\x1f\x8b\x08\x04\x00\x00\x00\x00\x00\xff\xaa\x00",  # FEXTRA, xlen, but no data # noqa: E501
+    b"\x1f\x8b\x08\x08\x00\x00\x00\x00\x00\xff",  # FNAME but no fname
+    b"\x1f\x8b\x08\x10\x00\x00\x00\x00\x00\xff",  # FCOMMENT, but no fcomment
+]
+
+
+@pytest.mark.parametrize("trunc", TRUNCATED_HEADERS)
+def test_truncated_header(trunc):
+    with pytest.raises(EOFError):
+        igzip.decompress(trunc)