Re: [9fans] Novice question - run as other

Re: [9fans] Novice question - run as other

[9nut]

> I'm missing something basic and cannot figure out. How can I run
> a program from a shell script and change the user it runs as.

The security model doesn't allow this. Perhaps by running it as a service
on a cpu.  Check /sys/src/cmd/auth/cron.c and cap(3).  For somethings
you can cpu over and change to a different uid:

% cpu  -a netkey
user[dvd]: glenda
challenge: 2304
response: 
etc.

You could also drawterm as a different user.

Re: [9fans] Novice question - run as other

[David Tolpin]

> > a program from a shell script and change the user it runs as.
>
> The security model doesn't allow this. Perhaps by running it as a service
> on a cpu.  Check /sys/src/cmd/auth/cron.c and cap(3).  For somethings
> you can cpu over and change to a different uid:

The following works:

cpu% cat > test.c
#include <u.h>
#include <libc.h>

void main(int argc,char **argv) {
	int fd = open("#c/user",OWRITE);

	if(argc==1) exits("argument required");
	fd>=0 && (write(fd,"none",strlen("none"))!=-1)
	|| (exits("cannot become none"),1);
	close(fd);

  	exec(argv[1], argv+1);
}
^D
cpu% 8c test.c
cpu% 8l test.8
cpu% 8.out /bin/rc -c 'while () {}'

In another window

cpu% ps -a|grep 8.out
none           4546    0:15   0:00     244K Ready    /bin/rc -c 'while () {}'

How can I do this without the code in C?

David

Re: [9fans] Novice question - run as other

[Geoff Collyer]

Switching to `none' is a special case.  You have to authenticate
cryptographically to become any other user.  If you want to really
become none and actually change your access rights, you have to do
more, notably newns().  See /bin/auth/none and its source.

Re: [9fans] Novice question - run as other

[David Tolpin]

> Switching to `none' is a special case.  You have to authenticate

I know that.

> cryptographically to become any other user.  If you want to really
> become none and actually change your access rights, you have to do

I want the process to be owned by none. 

> more, notably newns().  

Yes, I know that.

I didn't think it would help to add one more
call to the C code that did what it should. My puprose was to
ask whether I can do it from rc(1) without calling C programs.
If I can't that's fine, I just wanted to know whether I missed
something.

> See /bin/auth/none and its source.

OK. would help mentioning it in man somewhere.

David

Re: [9fans] Novice question - run as other

[David Tolpin]

> >> > a program from a shell script and change the user it runs as.
> >>
> >> The security model doesn't allow this. Perhaps by running it as a service
> >> on a cpu.  Check /sys/src/cmd/auth/cron.c and cap(3).  For somethings
> >> you can cpu over and change to a different uid:
> > 
> > The following works:
> ...
> > 	fd>=0 && (write(fd,"none",strlen("none"))!=-1)
>
> That's not what you asked.
>

? Is none not user?

cpu% grep none /adm/users
0:none:adm

cpu% none
cat /env/user
none

I want a program to run as a different user. From C, it means opening
'#c/user' and writing the user's name there. The security model is
a separate issue, the call either succeeds or fails, 
but it is a consequence of security limitations, and not of the API.

My question was how to do the same from rc. 

@{echo -n none > '#c/user' ; while() {sleep 1} }

succeeds but does not change the owner of the process. Why?

David

Re: [9fans] Novice question - run as other

[Geoff Collyer]

Regrettably auth/none is undocumented.  This sometimes happens.  You
do however have the sources and grep, and /sys/src/cmd/auth would have
been an obvious place to look.

I had been reserving judgement on whether or not you (David Tolpin)
really are the ungrateful punk that you appeared to be in all your
other interactions on 9fans.  I have now concluded that you are.  Many
of us have tried to help you, most of us civilly, and you've responded
like a spoiled snot-nosed kid who thinks he's entitled to answers and
that we have some obligation to provide them.  So I'm now deleting
your messages on contact.

Re: [9fans] Novice question - run as other

[Charles Forsyth]

>>My question was how to do the same from rc. 
>>@{echo -n none > '#c/user' ; while() {sleep 1} }
>>succeeds but does not change the owner of the process. Why?

aha! when that message arrived, i was just writing one to point out that you need to take
care that you stay in the same process as changes #c/user.  in the case above,
it does indeed change for the process that writes to #c/user (ie, the echo -n none)
but of course that process ends, and the parent shell carries on to run
	while() {...}
which happens in a different process from the echo!

Re: [9fans] Novice question - run as other

[David Tolpin]

> Regrettably auth/none is undocumented.  This sometimes happens.  You
> do however have the sources and grep, and /sys/src/cmd/auth would have
> been an obvious place to look.

But my question is not about authentication. My novice 
question is about a basic thing I don't understand about rc,
not about authentication.

The question has been stated clearly, and was not answered -- and
its your right not to answer it. But I have no use of answers to
questions I did not ask. auth/none does nothing httpd and listen do,
and I did read the code for them before asking.

> I had been reserving judgement on whether or not you (David Tolpin)
> really are the ungrateful punk that you appeared to be in all your
> other interactions on 9fans.  I have now concluded that you are.  Many
> of us have tried to help you, most of us civilly, and you've responded
> like a spoiled snot-nosed kid who thinks he's entitled to answers and
> that we have some obligation to provide them.  So I'm now deleting
> your messages on contact.

You are welcome.

David Tolpin

Re: [9fans] Novice question - run as other

[David Tolpin]

> >>My question was how to do the same from rc. 
> >>@{echo -n none > '#c/user' ; while() {sleep 1} }
> >>succeeds but does not change the owner of the process. Why?
>
> aha! when that message arrived, i was just writing one to point out that you need to take
> care that you stay in the same process as changes #c/user.  in the case above,
> it does indeed change for the process that writes to #c/user (ie, the echo -n none)
> but of course that process ends, and the parent shell carries on to run
> 	while() {...}
> which happens in a different process from the echo!
>

Thank you for the comment. I really don't realize a simple thing.
Will go and look into the source code of rc. I thought redirection
would mean I would modify rc's #c/user. I don't understand something
basic.

Thanks again

Re: [9fans] Novice question - run as other

[Charles Forsyth]

>>would mean I would modify rc's #c/user. I don't understand something
>>basic.

sorry, i ought to have added that #c/user changes per-process data,
not per-namespace data,
so it changes the data for the echo process, not for the rc.

/sys/src/9/port/auth.c:/^userwrite

userwrite(char *a, int n)
{
	if(n!=4 || strncmp(a, "none", 4)!=0)
		error(Eperm);
	kstrdup(&up->user, "none");	/* note use of up-> */
	up->basepri = PriNormal;
	return n;
}

Re: [9fans] Novice question - run as other

[Bruce Ellis]

it's funny that an astute colleague suggested that last week.
go out in the sun, mate!

geoff is not bad judge ...

brucee
----- Original Message ----- 
From: "Geoff Collyer" <geoff@collyer.net>
To: <9fans@cse.psu.edu>
Sent: Wednesday, March 17, 2004 7:55 PM
Subject: Re: [9fans] Novice question - run as other


> Regrettably auth/none is undocumented.  This sometimes happens.  You
> do however have the sources and grep, and /sys/src/cmd/auth would have
> been an obvious place to look.
> 
> I had been reserving judgement on whether or not you (David Tolpin)
> really are the ungrateful punk that you appeared to be in all your
> other interactions on 9fans.  I have now concluded that you are.  Many
> of us have tried to help you, most of us civilly, and you've responded
> like a spoiled snot-nosed kid who thinks he's entitled to answers and
> that we have some obligation to provide them.  So I'm now deleting
> your messages on contact.

Re: [9fans] Novice question - run as other

[David Tolpin]

> >>would mean I would modify rc's #c/user. I don't understand something
> >>basic.
>
> sorry, i ought to have added that #c/user changes per-process data,

> 	kstrdup(&up->user, "none");	/* note use of up-> */

Oh, many thanks. I said it was a novice question.

Re: [9fans] Novice question - run as other

[9nut]

>> > a program from a shell script and change the user it runs as.
>>
>> The security model doesn't allow this. Perhaps by running it as a service
>> on a cpu.  Check /sys/src/cmd/auth/cron.c and cap(3).  For somethings
>> you can cpu over and change to a different uid:
> 
> The following works:
...
> 	fd>=0 && (write(fd,"none",strlen("none"))!=-1)

That's not what you asked.

Re: [9fans] Novice question - run as other

[9nut]

You said:
>> >> > a program from a shell script and change the user it runs as.
and later
> ? Is none not user?

Are you trying to solve a real problem or win an argument?

Re: [9fans] Novice question - run as other

[boyd, rounin]

> I had been reserving judgement on whether or not you (David Tolpin)
> really are the ungrateful punk that you appeared to be in all your
> other interactions on 9fans.  I have now concluded that you are.

made that choice about a week ago.  i'm with you, captain.

Re: [9fans] Novice question - run as other

[Dave Lukes]

> > I had been reserving judgement on whether or not you (David Tolpin)
> > really are the ungrateful punk that you appeared to be in all your
> > other interactions on 9fans.  I have now concluded that you are.
> 
> made that choice about a week ago.  i'm with you, captain.

Metoo ... BUT ....

It ain't his fault: "I blame the system".

Now I don't want to get too mystical here but ...

I've been doing a lot of thinking recently, not just about plan9,
but also about life, the universe, me etc.,
and I realised the fundamental truth of the following:
        "We didn't want to lose the pleasant niche we occupied. What we
        wanted to preserve was just not a good environment in which to
        do programming, but a system around which a fellowship could
        form."
http://www.bell-labs.com/about/history/unix/somethingelse.html

To me, the last phrase is key: "fellowship".

People in general are far too used to paying software vendors to
spoonfeed them garbage.
To benefit from plan9 you have to understand and go with the flow
of its fundamental nature.

This is _not_ a product.

You are *not* entitled to
* pretty manuals,
* 0-800 support lines,
* annual upgrades
* virus scanners
* butt-kissing: if you're stupid, someone will tell you.

This is a community of people with a common interest.

You *are* entitled to:
* realise that you are part of something bigger than all of us
* work hard trying to understand it
* not piss the giants off by whining and shuffling from one foot
  to the other while you are standing on their shoulders
* sweat blood and carry boulders trying to make it better
* the wonderful feeling you get when something JUST WORKS.

If you can't get over this initial conceptual hump,
then fuck off back to CrapOS and leave us alone.

Dave out.

[9fans] insularity

[rog]

> So I'm now deleting your messages on contact.

oh for f***'s sake!

ok, so david tolpin has been a bit verbose, (and we're naturally
suspicious that his deep involvement with XML implies a fundamental
lack of taste) but when it comes down to it, he's has actually dived
in there and done stuff.

most newcomers to plan 9 don't get further than booting the damn
thing.

i think people that have been involved in this stuff for a long time
forget the distance between plan 9 and other systems.  yes, most stuff
is documented (often by implication), but having someone to talk to
that knows about the system makes all the difference.  i think all
david's questions have been perfectly acceptable, and i wouldn't have
thought twice about answering them had they been asked by someone
across the room.

this system *needs* people with some energy to spare, otherwise it'll
continue to decline the way it has been since the great scattering from
bell labs.  if this is the way we treat someone who appears to have
some energy and inclination, then i've no hope at all.  i'm ashamed to
be part of this group.

> If you can't get over this initial conceptual hump,
> then fuck off back to CrapOS and leave us alone.

*cringe*

Re: [9fans] insularity

[Aharon Robbins]

In article <6a2483a3e86ca91902d7199212d02f44@vitanuova.com> you write:
>i think people that have been involved in this stuff for a long time
>forget the distance between plan 9 and other systems.  yes, most stuff
>is documented (often by implication), but having someone to talk to
>that knows about the system makes all the difference.  i think all
>david's questions have been perfectly acceptable, and i wouldn't have
>thought twice about answering them had they been asked by someone
>across the room.
>
>this system *needs* people with some energy to spare, otherwise it'll
>continue to decline the way it has been since the great scattering from
>bell labs.  if this is the way we treat someone who appears to have
>some energy and inclination, then i've no hope at all.  i'm ashamed to
>be part of this group.

Hear, hear!  Well said.

Arnold

Re: [9fans] insularity

[suspect]

i stared at the last few messages to David with my mouth
open. Those were not very kind words to be spoken to
someone who has shown interest, willingness to actually
contribute and most importantly, humility.  Repeated humility.

I'm just an observer on this list, but feel obligated to speak up.
I'm also a dot/neato user. Thanks for the work. Thanks again.

cheers,


On Mar 17, 2004, at 11:22 AM, rog@vitanuova.com wrote:

>> So I'm now deleting your messages on contact.
>
> oh for f***'s sake!
>
> ok, so david tolpin has been a bit verbose, (and we're naturally
> suspicious that his deep involvement with XML implies a fundamental
> lack of taste) but when it comes down to it, he's has actually dived
> in there and done stuff.
>
> most newcomers to plan 9 don't get further than booting the damn
> thing.
>
> i think people that have been involved in this stuff for a long time
> forget the distance between plan 9 and other systems.  yes, most stuff
> is documented (often by implication), but having someone to talk to
> that knows about the system makes all the difference.  i think all
> david's questions have been perfectly acceptable, and i wouldn't have
> thought twice about answering them had they been asked by someone
> across the room.
>
> this system *needs* people with some energy to spare, otherwise it'll
> continue to decline the way it has been since the great scattering from
> bell labs.  if this is the way we treat someone who appears to have
> some energy and inclination, then i've no hope at all.  i'm ashamed to
> be part of this group.
>
>> If you can't get over this initial conceptual hump,
>> then fuck off back to CrapOS and leave us alone.
>
> *cringe*
>

Re: [9fans] insularity

[lucio]

> i stared at the last few messages to David with my mouth
> open. Those were not very kind words to be spoken to
> someone who has shown interest, willingness to actually
> contribute and most importantly, humility.  Repeated humility.

I'm going to add my voice to Pip's and especially Rog's.  I envy
David's ability to get things done in a totally novel environment (I'm
also a recent dot convert, thank you, David) and I have little trouble
sympathising with David's queries, understanding that not everyone is
as comfortable with English idioms as the Bell Labs ex-convicts are.

As for those who have spent time on this list just to deplore David's
behaviour, I believe they should put a bit more effort, in a
considerably less anglocentric fashion, to understand where some of us
come from and what we are able to contribute.

It is a shame that I should waste more bandwidth to do this.

++L

Re: [9fans] insularity

[Dave Lukes]

> oh for f***'s sake!

Careful: you're next:-).

> ok, so david tolpin has been a bit verbose, (and we're naturally
> suspicious that his deep involvement with XML implies a fundamental
> lack of taste)

Not the deep involvement:
I and at least one or 2 other people on this list have used XML,
but don't evangelise about it 'cos we know it's barfious.

>  but when it comes down to it, he's has actually dived
> in there and done stuff.

Cool, which means he's halfway there.

> most newcomers to plan 9 don't get further than booting the damn
> thing.

Which means that some people don't want to talk to them,
which is fine too!


> i think people that have been involved in this stuff for a long time
> forget the distance between plan 9 and other systems.

No, I continually thank my non-existent deity for that distance.

>   yes, most stuff
> is documented (often by implication), but having someone to talk to
> that knows about the system makes all the difference.

Yes, but expecting them to answer _all_ your questions is not useful.

>   i think all
> david's questions have been perfectly acceptable, and i wouldn't have
> thought twice about answering them had they been asked by someone
> across the room.

Fine.  We differ.

> this system *needs* people with some energy to spare, otherwise it'll
> continue to decline the way it has been since the great scattering from
> bell labs.

I don't see the benefit in involving people who don't "get it":
we'll end up with linux again.

Also, if plan9 dies, then maybe it will be down to bad luck,
or maybe it deserves to, because it ain't good enough.
If that is the case, then, in another few years,
some bright spark in a room somewhere will say,
"I know, let's write our own ..." and history will repeat itself.

>   if this is the way we treat someone who appears to have
> some energy and inclination, then i've no hope at all.

We treat everyone the same around here ...

>   i'm ashamed to
> be part of this group.

Then don't be.

I admit to being ashamed of my own brutality at times,
but the alternative (spoonfeeding people)
is far, far worse.

> > If you can't get over this initial conceptual hump,
> > then fuck off back to CrapOS and leave us alone.

> *cringe*

I stand by it:
if you're not willing to do the brainwork to understand the system,
don't use it.  It ain't Windows.

	Dave.

Re: [9fans] insularity

[Dave Lukes]

> I'm going to add my voice to Pip's and especially Rog's.  I envy
> David's ability to get things done in a totally novel environment (I'm
> also a recent dot convert, thank you, David) and I have little trouble
> sympathising with David's queries, understanding that not everyone is
> as comfortable with English idioms as the Bell Labs ex-convicts are.

It's not to do with english and queries,
it's to do with understanding the system.

As soon as I have time, I'm going to sweat reading the kernel
right the way through, just so I understand what's going on. 

> As for those who have spent time on this list just to deplore David's
> behaviour, I believe they should put a bit more effort, in a
> considerably less anglocentric fashion, to understand where some of us
> come from and what we are able to contribute.

I think you're being a bit unfair.

Re: [9fans] insularity

[vdharani]

rog,

i fully agree with you.

david, please dont feel bad. just ignore any negative comments and proceed
with what you are doing. we need more people into plan 9. i know how
difficult it is to bring people in. i know how easy it is to chase people
out. i wouldnt want a nice OS to disappear and show it to my grandchildren
in museum.

regards
dharani

>> So I'm now deleting your messages on contact.
>
> oh for f***'s sake!
>
> ok, so david tolpin has been a bit verbose, (and we're naturally
> suspicious that his deep involvement with XML implies a fundamental
> lack of taste) but when it comes down to it, he's has actually dived in
> there and done stuff.
>
> most newcomers to plan 9 don't get further than booting the damn
> thing.
>
> i think people that have been involved in this stuff for a long time
> forget the distance between plan 9 and other systems.  yes, most stuff
> is documented (often by implication), but having someone to talk to
> that knows about the system makes all the difference.  i think all
> david's questions have been perfectly acceptable, and i wouldn't have
> thought twice about answering them had they been asked by someone
> across the room.
>
> this system *needs* people with some energy to spare, otherwise it'll
> continue to decline the way it has been since the great scattering from
> bell labs.  if this is the way we treat someone who appears to have
> some energy and inclination, then i've no hope at all.  i'm ashamed to
> be part of this group.
>
>> If you can't get over this initial conceptual hump,
>> then fuck off back to CrapOS and leave us alone.
>
> *cringe*

Re: [9fans] insularity

[Latchesar Ionkov]

On Wed, Mar 17, 2004 at 05:53:13PM +0000, Dave Lukes said:
> I admit to being ashamed of my own brutality at times,
> but the alternative (spoonfeeding people)
> is far, far worse.

What is wrong with just ignoring the questions that require the spoonfeeding 
you are not willing to provide?

I also fully agree with Rog. 

	Lucho

Re: [9fans] insularity

[Fco.J.Ballesteros]

> As soon as I have time, I'm going to sweat reading the kernel
> right the way through, just so I understand what's going on. 

Although *a*lot* out of date, the Notes on the Plan 9 Kernel Sources
(see google) may help you to do that.

hth

Re: [9fans] insularity

[Geoff Collyer]

davel touches many of the relevant points.  I have no objection to
David asking questions, per se (though some of them did suggest a real
lack of effort, but that's not fatal).  I have no problem with David's
use of English, or anybody else's.  I'm glad to see others taking an
interest in Plan 9.

What I did, and do, object to is a persistently snarky attitude among
someone asking for help, particularly in response to answers intended
to be helpful and responsive to his questions, as the people answering
them understood them.  His apparent perception that we're all trying
to insult him (`I knew that.', `I knew that.') probably doesn't help
his attitude, but I don't believe that these apparently-perceived
insults were intended as insults.  If he can't find a way to get along
with people here without irritating large numbers of us frequently,
it's going to be an unpleasant experience for him and many of us.

Re: [9fans] insularity

[David Presotto]

It's too hard to read a person's attitude through mail
messages. Give it a rest please.

Re: [9fans] insularity

[boyd, rounin]

> oh for f***'s sake!

i see you can't spell.

Re: [9fans] insularity

[boyd, rounin]

> I'm going to add my voice to Pip's and especially Rog's.  I envy
> David's ability to get things done in a totally novel environment (I'm
> also a recent dot convert, thank you, David) ...

get things done?  cat /dev/noise

Re: [9fans] insularity

[boyd, rounin]

> If he can't find a way to get along
> with people here without irritating large numbers of us frequently,
> it's going to be an unpleasant experience for him and many of us.

as per usual, geoff is bang on the money.

Re: [9fans] insularity

[Dave Lukes]

> Although *a*lot* out of date, the Notes on the Plan 9 Kernel Sources
> (see google) may help you to do that.

I know, and I'm looking forward to that as well,
thanks, Nemo!

Cheers,
	Dave.

Re: [9fans] Novice question - run as other

[boyd, rounin]

> 1.  Anything you need to say to me you can say on 9fans.  Helps keep
> the story straight.

i'm with you, captain ...

Re: [9fans] Novice question - run as other

[Martin C.Atkins]

On Wed, 17 Mar 2004 22:00:45 +0400 (AMT) David Tolpin <dvd@davidashen.net> wrote:
> A more general conclusion is that for tasks where writing to
> or reading from files reflects or affects process space, and not
> name space, rc is not suitable and C code must be written.

Is it the process that writes to the device that gets altered,
or the process that opens the device?

I suspect the former, but why is it not the second? If it was the second,
then rc could probably be used, but what else wouldn't work, or would break?

Was the choice one of expediency, or is there a real semantic advantage
to the first choice?

Martin

-- 
Martin C. Atkins			martin@parvat.com
Parvat Infotech Private Limited		http://www.parvat.com{/,/martin}

Re: [9fans] Novice question - run as other

[rog]

> ip(3) ?

bind ether path

Re: [9fans] Novice question - run as other

[Russ Cox]

rog@vitanuova.com wrote:

>quite a few devices use this hack, often for efficiency reasons.
>
>ones i'm aware of include (aspects of) srv(3), ssl(3), tls(3), ip(3),
>cap(3), fs(3), dup(3) and cons(3)
>  
>

ip(3) ?

russ

Re: [9fans] Novice question - run as other

[rog]

> A more general conclusion is that for tasks where writing to
> or reading from files reflects or affects process space, and not
> name space, rc is not suitable and C code must be written.

that's not necessarily the case - only for something that changes
something in the writing process that isn't inherited by child
processes.

quite a few devices use this hack, often for efficiency reasons.

ones i'm aware of include (aspects of) srv(3), ssl(3), tls(3), ip(3),
cap(3), fs(3), dup(3) and cons(3)

Re: [9fans] Novice question - run as other

[plan9fans]

Hi,

My all-time favorite Unix story, lifted from
http://cm.bell-labs.com/cm/cs/who/dmr/hist.html

Although the multiple-process idea slipped in very easily indeed,
there were some aftereffects that weren't anticipated.  The most
memorable of these became evident soon after the new system came up
and apparently worked.  In the midst of our jubilation, it was
discovered that the chdir (change current directory) command had
stopped working.  There was much reading of code and anxious
introspection about how the addition of fork could have broken the
chdir call.  Finally the truth dawned: in the old system chdir was an
ordinary command; it adjusted the current directory of the (unique)
process attached to the terminal.  Under the new system, the chdir
command correctly changed the current directory of the process created
to execute it, but this process promptly terminated and had no effect
whatsoever on its parent shell!  It was necessary to make chdir a
special command, executed internally within the shell.  It turns out
that several command-like functions have the same property, for
example login.


-Steve

Re: [9fans] Novice question - run as other

[9nut]

In a private email to me, David Tolpin said:

>> You said:
>> >> >> > a program from a shell script and change the user it runs as.
>> and later
>> > ? Is none not user?
>>
>> Are you trying to solve a real problem or win an argument?
>>
> 
> I was trying to understand why #c/user does not obey the rules
> of namespaces. But I didn't know that I was trying to do that,
> what I did is that I could do an obvious thing with rc,
> and was asking for help. And Charles Forsyth explained the issue
> without resorting to offensive rants.
> 
> The art of listening to others is not yet well-developed on
> 9fans.
> 
> David

A couple of things: 

1.  Anything you need to say to me you can say on 9fans.  Helps keep
the story straight.

2. Are you saying that you did not ask:
	a. "Novice question - run as other" (from the subject line)
	b. "... from a shell script and change the user it runs as." (from your message)

If your question was truely about changing to "none" and not some
arbitrary user, then why not say "... - run as none", or "...  from a shell
script and change the user it runs as, to none".

you seem like a smart guy, and i would have no reason to think what you
asked is related to anything other than what you asked about.

Re: [9fans] Novice question - run as other

[David Presotto]

[-- Attachment #1: Type: text/plain, Size: 1068 bytes --]

You're confusing name space and semantics.  It is indeed in the name space
but the semantics of writing it is to change the state of the writer not
everyone who can see the name space.  Processes owned by different
users can all share objects in the same name space.  However reading or
writing those objects can have different permissions and results for
the different processes.

If I where to unbind /dev, all processes in that name space
would see that object disappear.

The discontinuity/incongruity in Plan 9 is what an object can see
about the process using it.  Kernel objects (things implemented with #x
for any x) can see the process and can adjust their behavior
on its immediate state (this is especially true of #p).  However
anything that goes through 9P only sees the user's state by way of
the messages sent to it.  It can't tell anything about the particular
process performing an action and can thus only adjust its semantics
according to the user who actually bound the object into its
name space (this action turns to an attach).

[-- Attachment #2: Type: message/rfc822, Size: 3102 bytes --]

From: David Tolpin <dvd@davidashen.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Novice question - run as other
Date: Wed, 17 Mar 2004 22:00:45 +0400 (AMT)
Message-ID: <200403171800.i2HI0jtq086906@adat.davidashen.net>

>
> >@{echo -n none > '#c/user' ; while() {sleep 1} }
>
> >succeeds but does not change the owner of the process. Why?
>
> well, seems it would be bad if all you had to do to change userid was 
> echo into '#c/user'
>
> So, starting from that, the why should be apparent.

The 'Why' was about a different issue.

The question was why the C program behaves differently than
the shell script.  The C program just writes to #c/user to
change the owner of the process.

The answer is that writing to #c/user is special
in the sense that although it is a part of namespace, it changes
the state of the process space, which is only apparent if you look
into the kernel source.

A more general conclusion is that for tasks where writing to
or reading from files reflects or affects process space, and not
name space, rc is not suitable and C code must be written.

I am now into the sources to understand which files in the namespace
are actually not in it, but in the process space.

David Tolpin
http://davidashen.net/

Re: [9fans] Novice question - run as other

[ron minnich]

On Wed, 17 Mar 2004, David Tolpin wrote:

> The question was why the C program behaves differently than
> the shell script.  The C program just writes to #c/user to
> change the owner of the process.

oops, sorry, missed it. Ignore me :-)

ron

Re: [9fans] Novice question - run as other

[David Tolpin]

>
> >@{echo -n none > '#c/user' ; while() {sleep 1} }
>
> >succeeds but does not change the owner of the process. Why?
>
> well, seems it would be bad if all you had to do to change userid was 
> echo into '#c/user'
>
> So, starting from that, the why should be apparent.

The 'Why' was about a different issue.

The question was why the C program behaves differently than
the shell script.  The C program just writes to #c/user to
change the owner of the process.

The answer is that writing to #c/user is special
in the sense that although it is a part of namespace, it changes
the state of the process space, which is only apparent if you look
into the kernel source.

A more general conclusion is that for tasks where writing to
or reading from files reflects or affects process space, and not
name space, rc is not suitable and C code must be written.

I am now into the sources to understand which files in the namespace
are actually not in it, but in the process space.

David Tolpin
http://davidashen.net/

Re: [9fans] Novice question - run as other

[rog]

> well, seems it would be bad if all you had to do to change userid was 
> echo into '#c/user'

but if echo was built in to the shell (as it is in some other systems)
that's all you *would* have to do!

Re: [9fans] Novice question - run as other

[David Presotto]

[-- Attachment #1: Type: text/plain, Size: 135 bytes --]

If all you wanted to do was change the user id, that
would be true.  However, without running newns() it's
kind of useless/dangerous.

[-- Attachment #2: Type: message/rfc822, Size: 1935 bytes --]

From: rog@vitanuova.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Novice question - run as other
Date: Wed, 17 Mar 2004 17:13:58 0000
Message-ID: <0e0cb432b6b2920c12c7b9bde24f0e27@vitanuova.com>

> well, seems it would be bad if all you had to do to change userid was 
> echo into '#c/user'

but if echo was built in to the shell (as it is in some other systems)
that's all you *would* have to do!

Re: [9fans] Novice question - run as other

[ron minnich]

>My question was how to do the same from rc. 

>@{echo -n none > '#c/user' ; while() {sleep 1} }

>succeeds but does not change the owner of the process. Why?

well, seems it would be bad if all you had to do to change userid was 
echo into '#c/user'

So, starting from that, the why should be apparent.

ron

Re: [9fans] Novice question - run as other

[David Presotto]

[-- Attachment #1: Type: text/plain, Size: 102 bytes --]

It worked, I believe you just didn't notice.  The echo process became
none and then immediately died.

[-- Attachment #2: Type: message/rfc822, Size: 2997 bytes --]

From: David Tolpin <dvd@davidashen.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Novice question - run as other
Date: Wed, 17 Mar 2004 12:54:46 +0400 (AMT)
Message-ID: <200403170854.i2H8sk2J083766@adat.davidashen.net>

> >> > a program from a shell script and change the user it runs as.
> >>
> >> The security model doesn't allow this. Perhaps by running it as a service
> >> on a cpu.  Check /sys/src/cmd/auth/cron.c and cap(3).  For somethings
> >> you can cpu over and change to a different uid:
> > 
> > The following works:
> ...
> > 	fd>=0 && (write(fd,"none",strlen("none"))!=-1)
>
> That's not what you asked.
>

? Is none not user?

cpu% grep none /adm/users
0:none:adm

cpu% none
cat /env/user
none

I want a program to run as a different user. From C, it means opening
'#c/user' and writing the user's name there. The security model is
a separate issue, the call either succeeds or fails, 
but it is a consequence of security limitations, and not of the API.

My question was how to do the same from rc. 

@{echo -n none > '#c/user' ; while() {sleep 1} }

succeeds but does not change the owner of the process. Why?

Dav id