A bug in the vfs_gpfs.c module

Richard Sharpe realrichardsharpe at gmail.com
Sat Apr 30 13:21:44 MDT 2011


I was tracking down a weird problem with the GPFS VFS module where I
currently work. The problem manifested itself in the following way:

1. User 1 creates a word file on a GPFS-hosted share. The ACL ends up
a little funky, with a funny special:owner@ ACE that seems to be
inherited from the parent dir. There is also a special:group@ ACE that
gives Domain Users all access, it seems.

2. User 2 edits the same word file and saves it. The ACL changes so
that now the first ACE is no longer special, but is user:User 1: same
permissions as owner@ had above [1]. Then there is the special:group@
ACE as before. The upshot is that User 2 now owns the file but only
has access via the group ACE and the UNIX permissions look like

3. User 2 does some more edits and tries to save the file. This time
around the save fails and User 2 is told that the file is READ ONLY or
in some cases PERMISSION DENIED (I think I have seen both).

After some investigation, and setting 'store dos attributes = yes' in
the smb.conf I found that there is a problem in the vfs_gpfs.c module
in the following way. When smbd/dosmode.c:dos_mode is called (perhaps
as a result of QPATHINFO):

1. in smbd/dosmode.c:get_ea_dos_attribute we find that it expects that
SMB_VFS_GETXATTR will return a blob that it then parses with

2. However, in modules/vfs_gpfs.c:gpfs_get_attr it uses the
compatibility mode for these things and tries to return
   a hex code:

        snprintf(attrstr, size, "0x%x", dosmode & SAMBA_ATTRIBUTES_MASK);
        DEBUG(10, ("gpfs_get_xattr: returning %s\n",attrstr));
        return size;

    Unfortunately, it seems now to create the incorrect info, since I
then see the following DEBUG info in the log file:

    DEBUG(1,("get_ea_dos_attributes: Badly formed DOSATTRIB on " ...);

which results in get_ea_dos_attribute failing and so,
smbd/dosmode.c:dos_mode, it falls back to dos_mode_from_sbuf, which
uses the UNIX permissions for the file, however, the UNIX permissions
are synthesized and in at least the case seen above, the owner of the
file does not have W permission, so Windows gets told that the file is
READONLY even though the ACL on the file would allow the owner access
via the group ACE.

I am still trying to understand whether or not things changed such
that the vfs_gpfs.c module is no longer returning the correct data, or
what. Any help would be appreciated.

Richard Sharpe

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