[PATCH][WIP] Make vfs_acl_xattr use hash of the posix ACL

[Andrew Bartlett]

On Fri, 2012-10-12 at 17:15 +0200, Alexander Werth wrote:
> 
> On Fri, 2012-10-12 at 14:18 +0200, Christian Ambach wrote:
> > Hi Andrew,
> > 
> > On 10/12/2012 01:26 PM, Andrew Bartlett wrote:
> > > By defining this interface, vfs_acl_common does not need to know what
> > > the system ACL is, be it posix or nfsv4 or AFS.  It can (if returned)
> > > just hash the contents of the data_blob and store it.
> > >
> > > At a later time, if the contents matches, then the exact NT ACL that
> > > the windows client set is returned.  If the hash does not match, the
> > > the posix, NFSv4 or AFS ACL must have been changed outside Samba,
> > > and an imperfect mapping to an NT ACL is returned instead. [...] I
> > > would welcome patches to linearise NFSv4 into NDR in the same way I
> > > did for posix ACLs in smb_acl.idl
> > 
> > Shouldn't we better have one datatype that fits all variants instead of
> > having datatypes for each style of ACL? And the common denominator here
> > would be the general Windows SD format (as it has all fidelity).
> 
> Using the xattr module on top of NFS4 can be useful to store local SIDs
> and to support some appliances that store arbitrary data in the ACL.
> And keep in mind that the VFS layer of samba allows to interface with
> custom filesystems. It's possible that the system can distinguish a call
> changing the ACL via smbd from a call through another program.
> 
> Maybe we need a VFS call that can be used to figure out if any ACL
> relevant information had been changed in the FS?
> What about a VFS function that accepts a hash and returns another one?
> A matching hash indicates that nothing changed and a changed one that
> something changed. Something like:
> static NTSTATUS vfs_acl_hash_changed(uint16_t hash_type,
>                                      uint8_t oldhash[SD_HASH_SIZE],
>                                      uint8_t *newhash[SD_HASH_SIZE]);
> 
> To save context switches it might be an option to return a pointer to
> the new security descriptor which will be needed anyway on a change.

I was specifically asked to keep the hashing code out of the ACL VFS
modules, which is why they instead put all the acl-relevent info (for
posix it's the ACL, user, group and mode) into a blob for vfs_acl_common
to hash. 

My original proposal (in May) was to have it the VFS modules return a
hash. 

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org