Clearing read-only file attribute from Windows guest result in world writable permission.

[JackieKu]

The shared folders of VirtualBox blindly maps read-only attribute of Windows guest to POSIX write permission. This behavior cause dangerous and undesired file permissions are set in the host system.

Steps to Reproduce

$ umask
0022
$ ls -l a.txt
-rw-r--r-- 1 user1 user1 0 Feb 10 00:00 a.txt

1. Set read-only attribute of the file "a.txt", from a Windows guest with the shared folder mounted.

   $ ls -l a.txt
   -r--r--r-- 1 user1 user1 0 Feb 10 00:00 a.txt
   

2. Unset read-only attribute of the same file, from the same Windows guest.

   $ ls -l a.txt
   -rw-rw-rw- 1 user1 user1 0 Feb 10 00:00 a.txt
   

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VirtualBox respects umask when only creating new files, but it should do the same when mapping read-only attribute (or something similar). Leaving files world writable is simply unacceptable.

[JackieKu]

Proposed fix