Shared My Documents folder not writable by non-root Linux guest

[srackham]

Host: Windows XP Pro SP2, Guest: Xubuntu 8.04

Non-root users can't write to a shared Windows 'My Documents' folder regardless of the 'uid' and 'gid'. Here's a transcript that illustrates the problem (the shared folder named mydocs shares the C:\Documents and Settings\srackham\My Documents folder and the logged on Xubuntu user is 'srackham'):

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$ ls -ld shared/
drwxr-xr-x 2 srackham srackham 4096 2008-09-18 07:59 shared/

$ sudo mount -t vboxsf -o uid=srackham,gid=srackham mydocs shared

$ ls -ld shared/
dr-xr-xr-x 1 srackham srackham 0 2008-09-18 10:15 shared/

$ touch shared/t
touch: cannot touch `shared/t': Permission denied

$ sudo touch shared/t

$ ls shared/t
shared/t

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Note how the user write bit on the mounted directory has been turned off so the user can't write but root can.

The problem seems to be related to the special properties imbued in the 'My Documents' folder by Windows. Same applies to the Windows 'Shared Documents' folder (`C:\Documents and Settings\All Users\Documents`).