Fixup imported windows media

Samba by default needs executable bit on files for them to be executable by windows.

Only give executable bits to .exe files that are PE32, mitigating the chance the executable bit could mean anything for Linux.
It could still mean something with binfmt misc hooks, but that shouldn't be done much.

confluent_server/confluent/osimage.py

@@ -648,6 +648,32 @@ def fixup_coreos(targpath):
                 bootimg.write(b'\x01')
 
 
+def is_windows_executable(filename):
+    with open(filename, 'rb') as f:
+        header = f.read(2)
+        if header == b'MZ':
+            # seems to be DOS, but let's also make sure it is PE32
+            f.seek(0x3c)
+            pe_offset = f.read(4)
+            offset = int.from_bytes(pe_offset, byteorder='little')
+            f.seek(offset)
+            pe_header = f.read(4)
+            if pe_header == b'PE\x00\x00':
+                return True
+    return False
+
+
+def fixup_windows(targpath):
+    # windows needs the executable file to be executable, which samba
+    # manifests as following the executable bit
+    for root, _, files in os.walk(targpath):
+        for fname in files:
+            if fname.endswith('.exe'):
+                fpath = os.path.join(root, fname)
+                if is_windows_executable(fpath):
+                    st = os.stat(fpath)
+                    os.chmod(fpath, st.st_mode | 0o111)
+
 def check_coreos(isoinfo):
     arch = 'x86_64'  # TODO: would check magic of vmlinuz to see which arch
     if 'zipl.prm' in isoinfo[1]: