Re: [PATCH] qga: Do not follow symlink in guest-ssh-* commands

On Mon, Aug 10, 2026 at 11:20 AM Daniel P. Berrangé <[email protected]>
wrote:

> On Mon, Aug 10, 2026 at 11:06:27AM +0300, Kostiantyn Kostiuk wrote:
> > Hi Valentino,
> >
> > Sorry for the long delay.
> > I have a question for you
> >
> > On Tue, Jul 14, 2026 at 7:10 PM Valentino Paulon <
> > [email protected]> wrote:
> >
> > > > > So, you propose to call seteuid/setegid before any I/O operation?
> > > >
> > > > Yes, specifically for the SSH commands, because they're unusual in
> > > > that we're doing stuff on behalf of an unprivileged user.
> > >
> > > +1 on the euid/egid direction -- as the reporter that's the outcome I
> > > was hoping for. It confines every step (read, mkdir, create, rename,
> > > chown) to what the target user could already do himself, which removes
> > > the whole TOCTOU class instead of chasing one instance of it.
> > >
> > > A few implementation details that tend to bite with this pattern, in
> > > case they save a round-trip:
> > >
> > > - drop the supplementary groups too, not just egid: initgroups() (or
> > > setgroups() with the user's list) while still root, otherwise the
> > > agent's effective access won't match the user's in either direction
> > >
> >
> > Technically, there is no limitation to running QGA in unprivileged mode.
> > Normally, it is a system daemon, but this is not mandatory.
> > In this case, we can not call initgroups because the caller must
> > have CAP_SETGID.
> > We can call initgroups only when QGA runs as root. What do you think?
>
> In any practical sense it is a system daemon given the set of commands
> it is exposing. Thus, IMHO, deploying as an unprivileged user should
> be considered a broken deployment. We could make that explicit by
> refusing to launch.
>

Makes sense, but we have one more issue with QGA unit tests in this case.
They are called by an unprivileged user (build user), and initgroups broke
it.
Is it possible to enter the namespace automatically by the test engine?


> With regards,
> Daniel
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