Re: [RCF] [PATCH] unprivileged mount/umount

[Bryan Henderson <hbryan@us.ibm.com>]

> So if a user creates a private namespace, it should have the choice of:
> 
>    1) Giving up all suid rights (i.e. all mounts are cloned and
>       propagated with nosuid)
> 
>    2) Not giving up suid for cloned and propagated mounts, but having
>       extra limitations (suid/sgid programs cannot access unprivileged
>       "synthetic" mounts)

(2) isn't realistic.  There's no such thing as a suid program.  Suid is a 
characteristic of a _file_.  There's no way to know whether a given 
executing program is running with privileges that came from a suid file 
getting exec'ed.  Bear in mind that that exec could be pretty remote -- 
done by a now-dead ancestor with three more execs in between.

Many user space programs contain hacks to try to discern this information, 
and they often cause me headaches and I have to fix them.  The usual hacks 
are euid==uid, euid==suid, and/or euid==0.  It would be an order of 
magnitude worse for the kernel to contain such a hack.

--
Bryan Henderson                          IBM Almaden Research Center
San Jose CA                              Filesystems
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