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SubjectRe: [RCF] [PATCH] unprivileged mount/umount
> 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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