On Sat, 23 Jan 1999, Albert D. Cahalan wrote:

> >>>> * Lack of generalized message passing
> >>>
> >>> (RT-signals in Linux, a feature of Linux 2.2) 
> >> 
> >> Could user acahalan send 42 bytes to user mmuscovi?
> >
> > sure, 'mail mmuscovi < ./42bytefile'. What are you trying to
> > achieve and why?
> 
> The original poster said "generalized message passing" and you
> responded with something that can pass 4 or 8 bytes between
> processes with the same UID. That isn't very general.

and my question is/was 'what do you need it for, exactly (ie. what
application)'.

> >>> (i guess you missed include/linux/capability.h, a feature of 2.2.
> >>> Not completely finished, but the main mechanizm is in there.)
> >> 
> >> I believe he means "true" capability support. In any case,
> >> Linux can't revoke normal user capabilities.
> >
> > what do you mean by 'true'.
> 
> True capability systems are token-based. They work very much like
> file descriptor security. Access can be passed from process to
> process, but is not automatically shared by all processes with the
> same UID. [...]

this is what Linux capabilities do too, if you care to take a look at the
code.

> We've often seen requests to deny users the ability to run a network
> server, and sometimes seen requests to deny users the ability to run a
> network client. [...]

this is perfectly possible with Linux capabilities, it just hasnt been
extended to above-port-1024 yet.

>           [...] I know I'd want to block SysV shared memory use if I
> were running a server with crummy users.

ulimit ...

> > take a look at async networking IO, fcntl(SETSIG), etc, implemented by
> > Stephen Tweedie recently. (it's in 2.2) 
> 
> Excellent - but only for network IO?

you are free to implement the rest.

-- mingo



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