[Samba] Samba permissions

[Scott Mayo]

Scott Mayo wrote:
> Keith Warno wrote:
> 
>> * <sgmayo at mail.bloomfield.k12.mo.us> [29/07/2005 1119EDT]:
>>
>>> I am working on my permissions and something does not quite make 
>>> sense to me.  Here is what I have set.
>>>
>>> /DIR          (Unix permissions are 3777)
>>>
>>> Then in samba I have the following
>>>
>>> [dir]
>>> path = /DIR
>>> read only = no
>>> valid users @teach @student
>>> create mask 3660
>>> directory mask 3770
>>>
>>> Then from a windows workstation, I create a new directory inside 
>>> 'dir', and call it 'teach'.
>>>
>>> The permissions of 'teach' are 2770.  It looks like it should be 3770 
>>> to me since the 'directory mask' commands does a bitwise 'AND'.  
>>> Anyone know why this is?  Maybe it is because of the DOS attributes 
>>> or something.
>>
>>
>>
>> You're right about the bitwise AND.
>>
>> But default mode for a new directory is 0777.  Observe:
>>
>> kw at pigpen[2]:~$ cd tmp
>> kw at pigpen[2]:~/tmp$ umask 0
>> kw at pigpen[2]:~/tmp$ umask
>> 0000
>> kw at pigpen[2]:~/tmp$ file foodir
>> foodir: cannot open (foodir)
>> kw at pigpen[2]:~/tmp$ mkdir foodir
>> kw at pigpen[2]:~/tmp$ ls -ld foodir
>> drwxrwxrwx  2 kw users 4096 Jul 29 11:59 foodir
>>
>> However, your new directory *inherited* the setgid bit (effectively a
>> bitwise OR); this is simply the behavior of setgid bits on directories.
>> From the man page for the stat() system call (section 2):
>>
>>        The set GID bit (S_ISGID) has several special uses: For a
>>        directory  it indicates  that  BSD  semantics is to be used for
>>        that directory: files created there inherit their group ID from
>>        the directory, not  from  the effective  gid  of  the creating
>>        process, and directories created there will also get the S_ISGID
>>        bit set.  For a file that does not  have  the group  execution
>>        bit (S_IXGRP) set, it indicates mandatory file/record locking.
>>
>> So, for your case:
>>
>>     (3770 & 0777) | 2000 = 2770
>>
>> It is doing exactly what it should be doing. :)
>>
>> Keith
> 
> 
> Ok, I guess that makes sense after you explained it.  I got it to work 
> by using both the 'directory mask' and the 'force directory mode'.  That 
> works but I have no idea why.  I also just tried to use the 'force 
> directory mode' which is a bitwise 'OR' to see what I would get and here 
> are the permissions that I end up with in both cases.  I cannot figure 
> out where they are coming from.
> 
> With both 'directory mask = 3770' and 'force directory mode = 3770' I get:
> 
> drwxrws--T DIR   (which would be 3770)
> 
> If I just use 'force directory mode = 3770', then I get the following 
> permissions:
> 
> drwxrwsr-t DIR   (which would be 3775)
> 
> Thanks for any help.  I am glad that it works in with using both 
> directives, but I just want to understand why.  I have been doing a  lot 
> of reading, and just when I think that I understand how it should 
> work...it throws me a curve. :)
> 

Actually the first one does make sense I guess, but not the 2nd.  Here 
is how I understand it.

[(3777 & 0770) | 3770] | 2000 = 3770

I have no ide where the rx permissions come from in the last example 
though.

-- 
Scott Mayo
Technology Coordinator
Bloomfield Schools
PH: 573-568-5669
FA: 573-568-4565
Pager: 800-264-2535 X2549

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