vfs_acl_xattr: objects without NT ACL xattr

vfs_acl_xattr: objects without NT ACL xattr

Even with "ignore system acls" set to "yes", for objects without NT ACL
xattr we use the underlying filesystem permissions to construct an NT
ACL. This can result in *very* unexpected permissions, eg:

- a directory with the following ACL:

$ ./bin/smbcacls -Uslow%pass //localhost/normal ""
REVISION:1
CONTROL:SR|DP
OWNER:SLOW\slow
GROUP:Unix Group\root
ACL:SLOW\slow:ALLOWED/0x0/FULL

So only one non-inheritable(!) ACE.

- creating a subdirectory:

$ ./bin/smbclient -Uslow%pass //localhost/normal -c "mkdir dir1"

- checking whether there's an ACL xattr:

$ getfattr -m "" /Volumes/normal/dir1
getfattr: Removing leading '/' from absolute path names
system.posix_acl_access
system.posix_acl_default
user.DOSATTRIB

So there isn't an ACL xattr, because there where no inheritable ACEs on
the parent folder.

- reading the new subdirectories ACL:

$ ./bin/smbcacls -Uslow%pass //localhost/normal "dir1"
REVISION:1
CONTROL:SR|DP
OWNER:SLOW\slow
GROUP:Unix Group\slow
ACL:SLOW\slow:ALLOWED/0x0/FULL
ACL:Unix Group\slow:ALLOWED/0x0/READ
ACL:Everyone:ALLOWED/0x0/READ
ACL:NT Authority\SYSTEM:ALLOWED/0x0/FULL

The ACES for "SLOW\slow", "Unix Group\slow" and "Everyone" are coming
from the underlying filesystem. This is the problem.

- Windows assigns the following ACL in this situation:

$ ./bin/smbcacls -UAdministrator%Passw0rd //10.10.10.14/data "dir"
REVISION:1
CONTROL:SR|PD|DI|DP
OWNER:VORDEFINIERT\Administratoren
GROUP:WIN2008R2\Domänen-Benutzer
ACL:WIN2008R2\Administrator:ALLOWED/0x0/FULL

$ ./bin/smbclient -UAdministrator%Passw0rd //10.10.10.14/data -c "mkdir dir\dir1"

$ ./bin/smbcacls -UAdministrator%Passw0rd //10.10.10.14/data "dir\dir1"
REVISION:1
CONTROL:SR|DI|DP
OWNER:VORDEFINIERT\Administratoren
GROUP:WIN2008R2\Domänen-Benutzer
ACL:VORDEFINIERT\Administratoren:ALLOWED/0x0/FULL
ACL:NT-AUTORITÄT\SYSTEM:ALLOWED/0x0/FULL

By changing make_default_filesystem_acl() to only adds user and system
ACE to the ACL of objects that lack an ACL xattr, we match Windows
behaviour:

$ ./bin/smbclient -Uslow%pass //localhost/normal -c "mkdir dir2"

$ ./bin/smbcacls -Uslow%pass //localhost/normal "dir2"
REVISION:1
CONTROL:SR|DP
OWNER:SLOW\slow
GROUP:Unix Group\slow
ACL:SLOW\slow:ALLOWED/0x0/FULL
ACL:NT Authority\SYSTEM:ALLOWED/0x0/FULL

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12028

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue Jul 19 10:22:05 CEST 2016 on sn-devel-144

(cherry picked from commit 961c4b591bb102751079d9cc92d7aa1c37f1958c)

Autobuild-User(v4-4-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-4-test): Thu Aug  4 14:49:18 CEST 2016 on sn-devel-144