[OpenAFS-devel] GIDs and file server permission checks

[Jeffrey Altman]

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On 10/25/2014 8:30 PM, Nathaniel W Filardo wrote:
> On Sat, Oct 25, 2014 at 07:07:10PM -0400, Jeffrey Altman wrote:
>> On 10/25/2014 3:35 PM, Nathaniel W Filardo wrote:
>>> Hello all,
>>>
>>> At present, GIDs seem a little funny -- it takes system:administrator=

>>> membership to change them, but files can be created with arbitrary GI=
D
>>> simply by operating a client with a UNIX credential whose primary GID=
 is
>>> whatever is desired.
>>
>> The actual requirements for setting the ownership and/or group of a
>> vnode are
>>
>>  1a. Insert permission on the directory
>>  1b. Ownership of the file
>>
>> or
>>
>>  2. Member of system:administrator group
>>
>> or
>>
>>  3a. Owner can be changed if the volume owner is the object owner
>>  3b. Group can be changed if the volume group is the object group

This should teach me to read code in a hurry.   The above is completely
wrong.

> Is this written down somewhere authoritative that I don't know about or=
 have
> forgotten?  (i.e. is there a specification document for the "operation =
X
> rights X UNIX permissions on special files" table)

IN the early 90s Transarc developed the protocol specification documents
that are located in doc/pdf/ in the source repository.  The fscm-ispec
pdf provides the documentation the community was given for the RXAFS
RPCs.  The AFSFetchStatus and AFSStoreStatus structures document the
"Group" fields as "not implemented".

The GetStatus() function in src/viced/afsfileprocs.c also comments that
the Group field is not implemented.  And yet, the Group field has been
set as far back as AFS 3.0.  If "partially implemented" is what was
meant by "not implemented", then that would explain why only the
system:administrators can set the values.

Unix mode group is not a property that will be set appropriately by
non-UNIX clients and might not be set properly by UNIX clients.  I do
not believe that the group value should be taken into account when the
file server is making decisions.

I believe the behavior should be as close as possible to that described
by POSIX http://www.unix.com/man-page/POSIX/1posix/chgrp/

  "Only the owner of a file or the user with appropriate privileges
    may change the owner  or group of a file."

For AFS I would interpret that as the group can be changed if any of the
following are true:

 1. the owner id of the file is the AFS ID of the issuer

 2. the issuer has "admin" privileges, the group

 3. the issuer is a member of system:administrators

However, this is protocol specification question and it should be
discussed on afs3-standardization before any implementation is accepted.

Jeffrey Altman







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