[PATCHES] Two patches for gpfs sharemodes

Christof Schmitt cs at samba.org
Thu Aug 24 17:18:42 UTC 2017

On Thu, Aug 24, 2017 at 12:31:10PM +0200, Ralph Böhme wrote:
> Hi Christof,
> On Wed, Aug 23, 2017 at 01:40:54PM -0700, Christof Schmitt via samba-technical wrote:
> > From 9474f1b1865636c7cc53a302b3225e3197f154c1 Mon Sep 17 00:00:00 2001
> > From: Christof Schmitt <cs at samba.org>
> > Date: Wed, 23 Aug 2017 10:33:42 -0700
> > Subject: [PATCH 1/2] vfs_gpfs: Do not map DELETE sharemode access to WRITE
> > 
> > A SMB client can deny the WRITE sharemode, but still grant the DELETE
> > sharemode. Mapping the requested DELETE access to WRITE access breaks
> > this case. Fix this by removing the incorrect mapping from DELETE access
> > to WRITE access.
> I'b be happy to review, alas I fail to understand gpfs_set_share()
> API/semantics. Would you or anyone else care to explain how the "allow" and
> "deny" parameters are supposed to work? Lacking API documentation for
> gpfs_set_share() makes me feel a bit uncomfortable when reviewing this...
> From looking at the semantics of the existing code set_gpfs_sharemode(), it
> seems as if "allow" is just used to pass the (mapped) access_mask to the
> filesystem. Supposedly GPFS then uses the "allow" parameter in a sense of
> "requested access" to match against possible deny modes from other opens?
> *scratches head*

I have done some extensive testing, so i am confident that this is

Samba can always open() a file and get a file descriptor. For other
applications, the file system will return an error on open() when there
is a conflicting sharemode for the file in the filesystem.

Through the "allow" parameter, Samba is registering the currently
required access to the file. This is somewhat redundant to the flags in
the open() call, but this is the path in the filesystem to prevent
conflicting sharemodes from other applications. As the gpfs_set_share
API is tied to a file descriptor, this does not include requesting
DELETE access, as this is done through unlink() without a file

The "deny" parameter is the inverse of the actual sharemode requested.
If the file is opened to allow only READ access for others, then
DENY_READ is not requested, but DENY_WRITE is.

The main point of the first patch is that when a SMB client is only
requesting READ and DELETE access, Samba should not request WRITE
access. A second access to the same file should be able to deny the
WRITE sharemode. The problem can be seen by running the
smb2.sharemode-access and smb2.access-sharemode tests against Samba
running on a gpfs file system. All combinations tested there are valid
against a Windows file server and a Samba server without the gpfs vfs
module. Loading the gpfs vfs module with gpfs:sharemodes=true results
in a test error that is fixed by the first patch here.


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