Samba create mask not working correctly

I have a samba share on a linux server (RHEL 6) that I am accessing via Windows 7.

I set the samba share with a create mask of 0664, but when I create files via samba from my Windows 7 machine, it creates the files with a permission level of 0674. If I edit a file, it changes its permissions to 0674 as well. If I remove the create mask for the share and rely on the default create mask of 0644, it creates files with permissions of 0774. My umask is 0022. I've tried a number of settings from the manual, but none seem to do the trick. Any ideas as to what is happening and how I can fix this?

Ideally, new files would have permission level of 0664 and existing files would maintain their permission level.

For reference, here's the output of testparm -v:

[global]
    dos charset = CP850
    unix charset = UTF-8
    display charset = LOCALE
    workgroup = WORKGROUP
    realm =
    netbios name = SERVER
    netbios aliases =
    netbios scope =
    server string = Bart
    interfaces =
    bind interfaces only = No
    security = DOMAIN
    auth methods =
    encrypt passwords = Yes
    update encrypted = No
    client schannel = Auto
    server schannel = Auto
    allow trusted domains = Yes
    map to guest = Never
    null passwords = No
    obey pam restrictions = No
    password server = passwordserver.domain.com
    smb passwd file = /var/lib/samba/private/smbpasswd
    private dir = /var/lib/samba/private
    passdb backend = tdbsam
    algorithmic rid base = 1000
    root directory =
    guest account = nobody
    enable privileges = Yes
    pam password change = No
    passwd program =
    passwd chat = *new*password* %n\n *new*password* %n\n *changed*
    passwd chat debug = No
    passwd chat timeout = 2
    check password script =
    username map =
    password level = 0
    username level = 0
    unix password sync = No
    restrict anonymous = 0
    lanman auth = No
    ntlm auth = Yes
    client NTLMv2 auth = No
    client lanman auth = No
    client plaintext auth = No
    preload modules =
    dedicated keytab file =
    kerberos method = default
    map untrusted to domain = No
    log level = 0
    syslog = 1
    syslog only = No
    log file = /var/log/samba/log.%m
    max log size = 10240
    debug timestamp = Yes
    debug prefix timestamp = No
    debug hires timestamp = Yes
    debug pid = No
    debug uid = No
    debug class = No
    enable core files = Yes
    smb ports = 445 139
    large readwrite = Yes
    max protocol = NT1
    min protocol = CORE
    min receivefile size = 0
    read raw = Yes
    write raw = Yes
    disable netbios = No
    reset on zero vc = No
    acl compatibility = auto
    defer sharing violations = Yes
    nt pipe support = Yes
    nt status support = Yes
    announce version = 4.9
    announce as = NT
    max mux = 50
    max xmit = 16644
    name resolve order = lmhosts wins host bcast
    max ttl = 259200
    max wins ttl = 518400
    min wins ttl = 21600
    time server = No
    unix extensions = No
    use spnego = Yes
    client signing = auto
    server signing = No
    client use spnego = Yes
    client ldap sasl wrapping = plain
    enable asu support = No
    svcctl list =
    deadtime = 0
    getwd cache = Yes
    keepalive = 300
    lpq cache time = 30
    max smbd processes = 0
    paranoid server security = Yes
    max disk size = 0
    max open files = 16384
    socket options = TCP_NODELAY
    use mmap = Yes
    hostname lookups = No
    name cache timeout = 660
    ctdbd socket =
    cluster addresses =
    clustering = No
    ctdb timeout = 0
    load printers = No
    printcap cache time = 750
    printcap name =
    cups server =
    cups encrypt = No
    cups connection timeout = 30
    iprint server =
    disable spoolss = No
    addport command =
    enumports command =
    addprinter command =
    deleteprinter command =
    show add printer wizard = Yes
    os2 driver map =
    mangling method = hash2
    mangle prefix = 1
    max stat cache size = 256
    stat cache = Yes
    machine password timeout = 604800
    add user script =
    rename user script =
    delete user script =
    add group script =
    delete group script =
    add user to group script =
    delete user from group script =
    set primary group script =
    add machine script =
    shutdown script =
    abort shutdown script =
    username map script =
    logon script =
    logon path = \\%N\%U\profile
    logon drive =
    logon home = \\%N\%U
    domain logons = No
    init logon delayed hosts =
    init logon delay = 100
    os level = 20
    lm announce = Auto
    lm interval = 60
    preferred master = No
    local master = No
    domain master = Auto
    browse list = Yes
    enhanced browsing = Yes
    dns proxy = Yes
    wins proxy = No
    wins server =
    wins support = No
    wins hook =
    kernel oplocks = Yes
    lock spin time = 200
    oplock break wait time = 0
    ldap admin dn =
    ldap delete dn = No
    ldap group suffix =
    ldap idmap suffix =
    ldap machine suffix =
    ldap passwd sync = no
    ldap replication sleep = 1000
    ldap suffix =
    ldap ssl = start tls
    ldap ssl ads = No
    ldap deref = auto
    ldap follow referral = Auto
    ldap timeout = 15
    ldap connection timeout = 2
    ldap page size = 1024
    ldap user suffix =
    ldap debug level = 0
    ldap debug threshold = 10
    eventlog list =
    add share command =
    change share command =
    delete share command =
    preload =
    lock directory = /var/lib/samba
    state directory = /var/lib/samba
    cache directory = /var/lib/samba
    pid directory = /var/run
    utmp directory =
    wtmp directory =
    utmp = No
    default service =
    message command =
    get quota command =
    set quota command =
    remote announce =
    remote browse sync =
    socket address = 0.0.0.0
    nmbd bind explicit broadcast = Yes
    homedir map = auto.home
    afs username map =
    afs token lifetime = 604800
    log nt token command =
    time offset = 0
    NIS homedir = No
    registry shares = No
    usershare allow guests = No
    usershare max shares = 0
    usershare owner only = Yes
    usershare path = /var/lib/samba/usershares
    usershare prefix allow list =
    usershare prefix deny list =
    usershare template share =
    panic action =
    perfcount module =
    host msdfs = Yes
    passdb expand explicit = No
    idmap backend = tdb
    idmap alloc backend =
    idmap cache time = 604800
    idmap negative cache time = 120
    idmap uid =
    idmap gid =
    template homedir = /home/%D/%U
    template shell = /bin/false
    winbind separator = \
    winbind cache time = 300
    winbind reconnect delay = 30
    winbind max clients = 200
    winbind enum users = No
    winbind enum groups = No
    winbind use default domain = No
    winbind trusted domains only = No
    winbind nested groups = Yes
    winbind expand groups = 1
    winbind nss info = template
    winbind refresh tickets = No
    winbind offline logon = No
    winbind normalize names = No
    winbind rpc only = No
    create krb5 conf = Yes
    comment =
    path =
    username =
    invalid users =
    valid users =
    admin users =
    read list =
    write list =
    printer admin =
    force user =
    force group =
    read only = Yes
    acl check permissions = Yes
    acl group control = No
    acl map full control = Yes
    create mask = 0744
    force create mode = 00
    security mask = 0777
    force security mode = 00
    directory mask = 0755
    force directory mode = 00
    directory security mask = 0777
    force directory security mode = 00
    force unknown acl user = No
    inherit permissions = No
    inherit acls = No
    inherit owner = No
    guest only = No
    administrative share = No
    guest ok = No
    only user = No
    hosts allow =
    hosts deny =
    allocation roundup size = 1048576
    aio read size = 0
    aio write size = 0
    aio write behind =
    ea support = No
    nt acl support = Yes
    profile acls = No
    map acl inherit = No
    afs share = No
    smb encrypt = auto
    block size = 1024
    change notify = Yes
    directory name cache size = 100
    kernel change notify = Yes
    max connections = 0
    min print space = 0
    strict allocate = No
    strict sync = No
    sync always = No
    use sendfile = No
    write cache size = 0
    max reported print jobs = 0
    max print jobs = 1000
    printable = No
    printing = cups
    cups options = raw
    print command =
    lpq command = %p
    lprm command =
    lppause command =
    lpresume command =
    queuepause command =
    queueresume command =
    printer name =
    use client driver = No
    default devmode = Yes
    force printername = No
    printjob username = %U
    default case = lower
    case sensitive = Auto
    preserve case = Yes
    short preserve case = Yes
    mangling char = ~
    hide dot files = Yes
    hide special files = No
    hide unreadable = No
    hide unwriteable files = No
    delete veto files = No
    veto files =
    hide files =
    veto oplock files =
    map archive = Yes
    map hidden = No
    map system = No
    map readonly = yes
    mangled names = Yes
    store dos attributes = No
    dmapi support = No
    browseable = Yes
    access based share enum = No
    blocking locks = Yes
    csc policy = manual
    fake oplocks = No
    locking = Yes
    oplocks = Yes
    level2 oplocks = Yes
    oplock contention limit = 2
    posix locking = Yes
    strict locking = Auto
    share modes = Yes
    dfree cache time = 0
    dfree command =
    copy =
    preexec =
    preexec close = No
    postexec =
    root preexec =
    root preexec close = No
    root postexec =
    available = Yes
    volume =
    fstype = NTFS
    set directory = No
    wide links = No
    follow symlinks = Yes
    dont descend =
    magic script =
    magic output =
    delete readonly = No
    dos filemode = No
    dos filetimes = Yes
    dos filetime resolution = No
    fake directory create times = No
    vfs objects =
    msdfs root = No
    msdfs proxy =

[path]
    comment = path
    path = /path/
    valid users = usera, userb, userc
    read only = No
    create mask = 0664
    directory mask = 0775
    wide links = Yes

Solution 1:

Often the issue is caused by enabling one of the following:

• map archive (uses unix execute bit for owner)
• map system (uses unix execute bit for group)
• map hidden (uses unix execute bit for other)
• inherit permissions causes samba to ignore create mask, etc
• there's also inherit acls which should default to no

"File Permissions and Attributes on MS-DOS and Unix" in Chapter 8. Advanced Disk Shares explains the above nicely.

However, microsoft office products cause weird behaviour and trigger a bug/unexpected behaviour. Even with create mask and/or force create mode set and avoiding the above map or inherit option, I've seen group execute permissions get set when editing documents using microsoft office applications. This doesn't happen with other programs, e.g. edit a .txt file with notepad and permissions stay sane. Office doesn't just create files, it also messes a bit with temp files, renaming and permissions.

After a lot of digging around, it might be also be mixed up with a Samba POSIX ACL bug of sorts:

• Old 2007 debian bug report "samba: misinterprets create mode with POSIX acls"
• "Wrong behaviour for default ACLs" seems to be the most recent bug report for samba, but is sadly closed 'RESOLVED INVALID' (prematurely?).

Observed behaviour on the Linux side

The extended ACLs for an empty word docx file created via windows explorer context menu (not yet opened and saved by word)

$ getfacl test.docx 
# file: test.docx
# owner: tester
# group: tester
user::rw-
group::rw-
other::---

After saving via MS word 2016

$ getfacl test.docx 
# file: test.docx
# owner: tester
# group: tester
user::rw-
user:tester:rw-
group::rw-
group:tester:rw-
mask::rwx

When checking the samba config, on Ubuntu 16.04 LTS, it seems map archive is enabled by default, but that should use the owner's execute bit, not the group execute bit, so that wasn't the cause in my case

$ testparm -s -v 2>&1 | grep 'map archive'
map archive = Yes

Observed behaviour on the Windows side

Using SysInternals Process Monitor and comparing editing a .txt file with notepad.exe vs. a .docx file with WINWORD.EXE, the office suite does a lot of fancy footwork creating temp files, renaming, etc. In particular, unlike notepad.exe, WINWORD.EXE seems to fiddle with access control lists. As seen by procmon

SetSecurityFile
Information:    Group, DACL

So I suspect this is why the UNIX group permission gets fiddled with by microsoft office applications.

Deeper investigation required turning on windows file object security auditing to see what exactly changed. Event ID 4670 shows the the ~WRD0000.tmp permission changes applied (I think word uses this for periodic saving and recovery if it crashes).

Object:
    Object Server:    Security
    Object Type:    File
    Object Name:    C:\Users\<user>\Desktop\TestAudit\~WRD0000.tmp
    Handle ID:    0xfd0

Process:
    Process ID:    0x1ae4
    Process Name:    C:\Program Files\Microsoft Office\root\Office16\WINWORD.EXE

Permissions Change:
    Original Security Descriptor:
D:AI(A;ID;FA;;;SY)(A;ID;FA;;;BA)(A;ID;FA;;;S-1-5-<SID>-1001)
    New Security Descriptor:
D:(A;;0x1200a9;;;WD)(A;ID;FA;;;SY)(A;ID;FA;;;BA)(A;ID;FA;;;S-1-5-21-<SID>-1001)

The permission change in SDDL (Security Descriptor Definition Language) is a DACL (discretionary access control list part) where it appears an extra ACE (Access Control Entry) was added. ACE (A;;0x1200a9;;;WD) gets added right at the front. This is how I interpreted it:

• A; meaning allow access, stayed the same
• ; no inheritance
• 0x1200a9; means FILE_GENERIC_READ | FILE_EXECUTE read & execute access
• WD means the 'everyone' trustee

Then later on, the ~WRD0000.tmp gets renamed to test.docx which I saw in process monitor as a SetRenameInformationFile operation. So in the end test.docx ends up with some of the ACE changes word did for whatever reason.