Default ACLs and the ACL hash in vfs_xattr_common

Jeremy Allison jra at
Fri Oct 5 09:41:32 MDT 2012

On Fri, Oct 05, 2012 at 03:47:20PM +1000, Andrew Bartlett wrote:
> Jeremy,
> I've been looking over the ACL mapping code and in particular the
> hash-based method in vfs_xattr_common.
> It is complex code, and so I'm trying to validate what I'm reading.  As
> far as I see it, the inclusion (or not) of the default ACL on a
> directory in the ACL calculation depends on if we call
> fget_nt_acl_common or get_nt_acl_common.
> This in turn makes me worry that the hashed SD (created with
> fget_nt_acl_common) will not match for directories where we call
> get_nt_acl_common, which might consider a default posix ACL. 
> This is due to the difference between posix_fget_nt_acl() and
> posix_get_nt_acl() in posix_acls.c
> The reason this comes to light for me now is that I'm looking to make
> this more reliable, and hash the posix ACL.  I've made preparations
> before rc1, but I need to finish the work, and noticed the need to
> consider these default ACLs. 
> I'll keep digging, but I just thought I might raise the issue. 

Thanks for checking, but I don't think this occurs.

posix_get_nt_acl() reads the default ACL if it's a directory.

Inside posix_fget_nt_acl() we have:

       if (fsp->is_directory ||  fsp->fh->fd == -1) {
                return posix_get_nt_acl(fsp->conn, fsp->fsp_name->base_name,
                                        security_info, ppdesc);

So if it is a directory (which we know from the fsp pointer, and is
the only case where we can have a default ACL) then we simply return
posix_get_nt_acl(), which does fetch the default ACL.

I think you missed that in the control flow.



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