1 Aug
2019
1 Aug
'19
12:35 p.m.
Read and write permission were common ideas--even part of
the Atlas paging hardware that was described before 1960.
The original concept of time-sharing was to give a virtual
computer to each user. When it became clear that sharing
was an equally important aspect, owner/other permissions
arose. I believe that was the case with Multics.
Owner/other permissions were in PDP-11 Unix from the start.
Group permissions arose from the ferment of daily talk in
the Unix lab. How might the usual protections be extended
to collaborative projects? Ken and Dennis deserve credit
for the final implementation. Yet clean as the idea of groups
was, it has been used only sporadically (in my experience).
Execute permission (much overloaded in Unix) also dates
back to the dawn of paging. One Unix innovation, due to
Dennis, was the suid bit--the only patented feature in
the Research system. It was instantly adopted for
maintaining the Moo (a game now sold under the name
"Master Mind") league standings table.
One trouble with full-blown ACLs as required by NSA's
Orange Book, is obscurity. It is hard (possibly NP-
complete) to analyze the actual security of an ACL
configuration.
A common failing of Unix administration was a proliferation
of suid-root programs, e.g. mail(1). I recall one system
that had a hundred such programs. Sudo provided a way
station between suid and ACLs.
Doug
1 Aug
1 Aug
4:22 p.m.
New subject: Who's behind the UNIX filesystem permission
*Yet clean as the idea of groups was, it has been used only sporadically
(in my experience).*
As I recall it, the original "basic groups" were essentially "us" and
"them". "Us" was everyone in the "in crowd",
"them" was everyone else.
Since the basic groups were rather extensive, it was prudent to turn group
write permission off in your default umask. But that made groups rather
clunky. You were in only one group at a time, so you had to "chgrp" to a
select group, and then remember to set your umask to allow group write
permission so others in the group could modify files. This changed when you
could be in multiple groups at the same time (a BSD invention?), and your
primary group automatically changed to the group owning your current
working directory (iff you belonged to that group). This made it
unnecessary to do an explicit chgrp in most cases. Having group write
permission off in your default umask was now a nuisance. We fixed that by
giving everyone an unshared primary group id, typically the same as the
uid. It then became safe to make group write permission on by default. This
made groups much more useful. Anyone in a group (but only those members)
could create a directory owned by that group, and group members working in
that directory defaulted to creating files (and subdirectories) group-owned
by and writable by all the members of the group. It just worked.
On Thu, Aug 1, 2019 at 8:36 AM Doug McIlroy <doug(a)cs.dartmouth.edu> wrote:
Read and write permission were common ideas--even part
of
the Atlas paging hardware that was described before 1960.
The original concept of time-sharing was to give a virtual
computer to each user. When it became clear that sharing
was an equally important aspect, owner/other permissions
arose. I believe that was the case with Multics.
Owner/other permissions were in PDP-11 Unix from the start.
Group permissions arose from the ferment of daily talk in
the Unix lab. How might the usual protections be extended
to collaborative projects? Ken and Dennis deserve credit
for the final implementation. Yet clean as the idea of groups
was, it has been used only sporadically (in my experience).
Execute permission (much overloaded in Unix) also dates
back to the dawn of paging. One Unix innovation, due to
Dennis, was the suid bit--the only patented feature in
the Research system. It was instantly adopted for
maintaining the Moo (a game now sold under the name
"Master Mind") league standings table.
One trouble with full-blown ACLs as required by NSA's
Orange Book, is obscurity. It is hard (possibly NP-
complete) to analyze the actual security of an ACL
configuration.
A common failing of Unix administration was a proliferation
of suid-root programs, e.g. mail(1). I recall one system
that had a hundred such programs. Sudo provided a way
station between suid and ACLs.
Doug
4:35 p.m.
New subject: Who's behind the UNIX filesystem permission
There's also the setgid bit on directories, that when files are created,
they will be in the group that the parent directory has on it.
Also, I don't think it's been mentioned, but there's the setuid bit on
directories - otherwise known as the sticky bit. When set, even if you
have rights to "write" the directory (meaning, delete files), you can't
delete those owned by other users. Useful for /tmp
I have no idea what the timeline is for either of these features :)
On 8/1/2019 12:22 PM, John P. Linderman wrote:
*Yet clean as the idea of groups was, it has been used only
sporadically (in my experience).*
As I recall it, the original "basic groups" were essentially "us" and
"them". "Us" was everyone in the "in crowd",
"them" was everyone else.
Since the basic groups were rather extensive, it was prudent to turn
group write permission off in your default umask. But that made groups
rather clunky. You were in only one group at a time, so you had to
"chgrp" to a select group, and then remember to set your umask to
allow group write permission so others in the group could modify
files. This changed when you could be in multiple groups at the same
time (a BSD invention?), and your primary group automatically changed
to the group owning your current working directory (iff you belonged
to that group). This made it unnecessary to do an explicit chgrp in
most cases. Having group write permission off in your default umask
was now a nuisance. We fixed that by giving everyone an unshared
primary group id, typically the same as the uid. It then became safe
to make group write permission on by default. This made groups much
more useful. Anyone in a group (but only those members) could create a
directory owned by that group, and group members working in that
directory defaulted to creating files (and subdirectories) group-owned
by and writable by all the members of the group. It just worked.
2 Aug
2 Aug
8:35 a.m.
New subject: Additional groups and additional directory permissions
[Subject line changed]
Hi.
Doug McIlroy:
Yet clean as the idea of groups was, it has been used
only sporadically
(in my experience).
I suspect this was true mainly at Research, where the whole place was
not large. Other people, as pointed out, found groups to be very useful.
"John P. Linderman" <jpl.jpl(a)gmail.com> wrote:
This changed when you
could be in multiple groups at the same time (a BSD invention?),
Yes, at 4.2 BSD. The so-called group set.
and your
primary group automatically changed to the group owning your current
working directory (iff you belonged to that group).
No. Your process simply carried around a bunch of groups with it, and if
the group of the directory matched the primary group or a member of the
group set, you got group permission.
Arthur Krewat <krewat(a)kilonet.net>et>:
There's also the setgid bit on directories, that
when files are created,
they will be in the group that the parent directory has on it.
IIRC this was a Sun invention. It was in SunOS 4.x, and may even have
been in SunOS 3.x.
Also, I don't think it's been mentioned, but
there's the setuid bit on
directories - otherwise known as the sticky bit. When set, even if you
have rights to "write" the directory (meaning, delete files), you can't
delete those owned by other users. Useful for /tmp
Also a SunOS invention, IIRC.
I have no idea what the timeline is for either of
these features :)
Timeline is late 80s, SunOS 4.0, I believe. (Larry? :-)
These ideas later propogated into SVR4 / Solaris, Linux and most (if not all)
the other proprietary Unixes.
HTH,
Arnold
11:18 a.m.
New subject: Additional groups and additional directory permissions
arnold(a)skeeve.com <arnold(a)skeeve.com> wrote:
BSD again :-) SCCS revision 6.6 so I think it appeared in 4.3BSD
https://svnweb.freebsd.org/csrg/sys/ufs/ffs/ufs_lookup.c?r1=15809&r2=16…
Tony.
--
f.anthony.n.finch <dot(a)dotat.at> http://dotat.at/
Mull of Galloway to Mull of Kintyre including the Firth of Clyde and North
Channel: Variable 1 to 3, becoming easterly or southeasterly 2 to 4 later.
Smooth, occasionally slight at first in North Channel. Showers for a time near
shore. Good.
Arthur Krewat <krewat(a)kilonet.net>et>:
When Bill Joy added the "multi-group stuff" to BSD all directories became
implicitly set-gid:
https://svnweb.freebsd.org/csrg/sys/ufs/ffs/ffs_inode.c?r1=4818&r2=5855
This is in SCCS revision 4.8 so I think it appeared in 4.2BSD
As I understand it, when group support was improved in System V they did
not change creat() to match BSD but instead used the directory set-gid bit
to provide opt-in BSD semantics. I don't know if this was in Solaris or
earlier?
There's also the setgid bit on directories,
that when files are created,
they will be in the group that the parent directory has on it.
IIRC this was a Sun invention. It was in SunOS 4.x, and may even have
been in SunOS 3.x. Also, I
don't think it's been mentioned, but there's the setuid bit on
directories - otherwise known as the sticky bit. When set, even if you
have rights to "write" the directory (meaning, delete files), you can't
delete those owned by other users. Useful for /tmp
Also a SunOS invention, IIRC.
4 Aug
4 Aug
6:40 a.m.
New subject: Additional groups and additional directory permissions
arnold(a)skeeve.com <arnold(a)skeeve.com> wrote:
> Arthur Krewat <krewat(a)kilonet.net>et>:
> > There's also the setgid bit on directories, that when files are created,
> > they will be in the group that the parent directory has on it.
>
> IIRC this was a Sun invention. It was in SunOS 4.x, and may even have
> been in SunOS 3.x.
Tony Finch <dot(a)dotat.at> wrote:
When Bill Joy added the "multi-group stuff"
to BSD all directories became
implicitly set-gid:
Yes. But the commercial world had backwards compatibility to worry about.
Thus the setgid bit on directories. I'm no longer sure who first came
up with it.
As I understand it, when group support was improved in
System V they did
not change creat() to match BSD but instead used the directory set-gid bit
to provide opt-in BSD semantics. I don't know if this was in Solaris or
earlier?
Correct, but not sure when it was first done.
Also, I don't think it's been mentioned, but
there's the setuid bit on
directories - otherwise known as the sticky bit. When set, even if you
have rights to "write" the directory (meaning, delete files), you can't
delete those owned by other users. Useful for /tmp
Also a SunOS invention, IIRC.
2 Aug
2 Aug
12:45 p.m.
New subject: Additional groups and additional directory permissions
On 8/2/2019 4:35 AM, arnold(a)skeeve.com wrote:
[Subject line changed]
Hi.
Arthur Krewat <krewat(a)kilonet.net>et>:
Makes a lot of sense. I just fired up my Consensys SVR4.2 VirtualBox
guest, and sure enough, neither the sticky bit, nor setgid work on
directories.
My first commercial experience with UNIX as a consultant was SunOS. I
had worked on Version 6 earlier, but that was purely personal and never
more than messing around with a uVAX a friend had brought home from work.
thanks for the info!
art k.
There's also the setgid bit on directories,
that when files are created,
they will be in the group that the parent directory has on it.
IIRC this was a Sun
invention. It was in SunOS 4.x, and may even have
been in SunOS 3.x.
Also, I don't think it's been
mentioned, but there's the setuid bit on
directories - otherwise known as the sticky bit. When set, even if you
have rights to "write" the directory (meaning, delete files), you can't
delete those owned by other users. Useful for /tmp
Also a SunOS invention, IIRC.
I have no idea what the timeline is for either of
these features :)
Timeline is late 80s, SunOS 4.0, I believe. (Larry? :-)
These ideas later propogated into SVR4 / Solaris, Linux and most (if not all)
the other proprietary Unixes.
1:06 p.m.
New subject: Additional groups and additional directory permissions
On Fri, Aug 2, 2019 at 4:36 AM <arnold(a)skeeve.com> wrote:
Arthur Krewat <krewat(a)kilonet.net>et>:
Nope, much older. It was a BSDism -- Cory Hall 11/70 actually (V6
originally) - wnj probably, but it may have been somebody like Asa
Romberger or Bob Kriddle who were the admins. VAXen distributions picked
it up and Sun got it from there.
Also, I don't think it's been
mentioned, but there's the setuid bit on
directories - otherwise known as the sticky bit. When set, even if you
have rights to "write" the directory (meaning, delete files), you can't
delete those owned by other users. Useful for /tmp
Also a SunOS invention, IIRC.
1:28 p.m.
New subject: Additional groups and additional directory permissions
The best I can tell/remember is that groups went through 4 phases:
1.) No groups (earliest UNIX) [ I personally never used this except in the
V0 retrocomputing]
2.) First group implementation (Thompson) [My first UNIX introduction was
with this implementation]
3.) PWB 1.0 (Mashey version) [then saw this post PWB]
4.) BSD 4.2 (wnj version) [and lived this transistion]
Each was a little different in semantics.
As Doug mentioned, many sites (like Research) really did not need much and
groups were really not used that widely. Thompson added something like
the Project number of TOPS and some earlier systems. Truth is, it did not
help much IMO. It was useful for grouping things like the binaries and
keeping some more privileged programs from having to be setuid root.
Mashey added features in PWB, primarily because of the RJE/Front end to the
Mainframes and the need to have better protections/collections of certain
items. But they still were much more like the DEC PPN, were you were
running as a single group (i.e. the tuple UID/GID). This lasted a pretty
long time, as it worked reasonably well for larger academic systems, where
you had a user and were assigned a group, say for a course or class, you
might be talking. If you looked at big 4.1 BSN Vaxen like at Purdue/Penn
State, *etc.*, that how they were admin'd. But as Doug said, if you were
still a small site, the use of groups was still pretty shallow.
But, as part of the CSRG support for DARPA, there was a push from the
community to have a list of groups that a user could be a part and you
carried that list around in a more general manner. The big sites, in
particular, were pushing for this because they were using groups as a major
feature. wnj implemented same and it would go out widely in 4.2, although
>by memory<< that was in 4.1B or 4.1C first.
It's possible Robert Elz
may have brought that to Bill with his quota changes,
but frankly I've
forgotten. There was a lot of work being done to the FS at that point,
much less Kirk's rewrite.
But as UNIX went back to workstations, the need for a more general group
system dropped away until the advent widely used distributed file systems
like CMU's AFS and Sun's NFS. Then the concept of a user being in more
than one group became much more de rigeur even on a small machine.
Clem
7 p.m.
New subject: Additional groups and additional directory permissions
isn't Kirk McKusic a member of our group? Guess he can contribute a lot on this
issue.
--- Ursprüngliche Nachricht ---
Von: Clem Cole <clemc(a)ccc.com>
Datum: 02.08.2019 15:28:18
An: Aharon Robbins <arnold(a)skeeve.com>om>, Doug McIlroy <doug(a)cs.dartmouth.edu>
Betreff: Re: [TUHS] Additional groups and additional directory permissions
The best I can tell/remember is that groups went
through 4 phases:
1.) No groups (earliest UNIX) [ I personally never used this except in the
V0 retrocomputing]
2.) First group implementation (Thompson) [My first UNIX introduction was
with this implementation]
3.) PWB 1.0 (Mashey version) [then saw this post PWB]
4.) BSD 4.2 (wnj version) [and lived this transistion]
Each was a little different in semantics.
As Doug mentioned, many sites (like Research) really did not need much and
groups were really not used that widely. Thompson added something like
the Project number of TOPS and some earlier systems. Truth is, it did not
help much IMO. It was useful for grouping things like the binaries and
keeping some more privileged programs from having to be setuid root.
Mashey added features in PWB, primarily because of the RJE/Front end to the
Mainframes and the need to have better protections/collections of certain
items. But they still were much more like the DEC PPN, were you were
running as a single group (i.e. the tuple UID/GID). This lasted a pretty
long time, as it worked reasonably well for larger academic systems, where
you had a user and were assigned a group, say for a course or class, you
might be talking. If you looked at big 4.1 BSN Vaxen like at Purdue/Penn
State, *etc.*, that how they were admin'd. But as Doug said, if you were
still a small site, the use of groups was still pretty shallow.
But, as part of the CSRG support for DARPA, there was a push from the
community to have a list of groups that a user could be a part and you
carried that list around in a more general manner. The big sites, in
particular, were pushing for this because they were using groups as a major
feature. wnj implemented same and it would go out widely in 4.2, although
>by memory<< that was in 4.1B or 4.1C
first. It's possible
Robert Elz
may have brought that to Bill with his quota changes, but frankly I've
forgotten. There was a lot of work being done to the FS at that point,
much less Kirk's rewrite.
But as UNIX went back to workstations, the need for a more general group
system dropped away until the advent widely used distributed file systems
like CMU's AFS and Sun's NFS. Then the concept of a user being in more
than one group became much more de rigeur even on a small machine.
Clem
1 Aug
1 Aug
5:01 p.m.
New subject: Who's behind the UNIX filesystem permission
On 08/01/19 08:35, Doug McIlroy wrote (in part):
Yet clean as the idea of groups
was, it has been used only sporadically (in my experience).
Interesting... we used
groups extensively (qa, staging, dev, research,
release, ...) but never ACLs.
N.
6:26 p.m.
New subject: Who's behind the UNIX filesystem permission
On 8/1/2019 1:01 PM, Nemo Nusquam wrote:
On 08/01/19 08:35, Doug McIlroy wrote (in part):
I've had occasion to use groups extensively in various places I've
consulted. Defense Contractors, educational institutions, etc. That, and
quotas.
I've used Solaris ZFS ACLs, and Linux ACLs to solve many problems.
There's always an exception to the UNIX rule when it comes to
owner/group/world, and trying to corral users into that paradigm is not
always fruitful.
Although, in one case, a common storage area with both the setgid and
setuid bit on the parent, and various Engineering departments writing
files and directories to it, was a really cool solution to a problem
although it used secondary groups as well.
art k.
Yet clean as the idea of groups
was, it has been used only sporadically (in my experience).
Interesting... we used
groups extensively (qa, staging, dev, research,
release, ...) but never ACLs. 
8:14 p.m.
New subject: Who's behind the UNIX filesystem permission
Two things killed off the adoption of groups as a widely-deployed
ACL mechanism:
1) NFS, specifically its limits on the number of supplimentary groups
the protocol supported,
2) Kernel limits on the number of supplimentary groups associated with
a process (e.g. NGROUPS_MAX)
--lyndon
9:23 p.m.
New subject: Who's behind the UNIX filesystem permission
On Thu, 1 Aug 2019, Doug McIlroy wrote:
A common failing of Unix administration was a
proliferation of suid-root
programs, e.g. mail(1). I recall one system that had a hundred such
programs. Sudo provided a way station between suid and ACLs.
I've always maintained that if you think you need setuid root (which is a
gaping chest wound), you can invariably get away with setgid instead.
ObTrivia: Back in the 80s, some third-party software needed to be
installed under "root". I was suspicious, but I had little choice but to
allow it (manager's orders; that company went under shortly after I left
them). Eventually I discovered why, when I had to clean up the mess: it
actually *unlinked* directories; yes, you read that right...
-- Dave
1721
days inactive
1724
days old
13 comments
10 participants
participants (10)
-
arnold＠skeeve.com -
Arthur Krewat -
Clem Cole -
Dave Horsfall -
Doug McIlroy -
John P. Linderman -
Lyndon Nerenberg -
Nemo Nusquam -
Thomas Paulsen -
Tony Finch