os-prober expects to run in a new private mount namespace, but new namespace is not private

[Olivier Gayot]

During execution of os-prober, other processes on the system can see the
temporary mounts to /var/lib/os-prober/mount even though os-prober runs
in a separate mount namespace.

In order to run os-prober in a more isolated mode, we introduced the
newns.c source file a while ago. We build it to a binary and ship it in
os-prober and os-prober-udeb.

The original idea was to run os-prober in a private mount namespace.
Sadly, calling the unshare(CLONE_NEWNS) system call is only enough to
create a new mount namespace. But it is not enough to make the new
namespace private.

While we can patch newns.c to make the new mount namespace private,
relying on unshare(1) from util-linux (which is an essential package)
seems like a more viable option.

[Olivier Gayot (ogayot)]

Adding debdiff removing the flawed newns binary and replacing it by the use of unshare. unshare --mount creates a private mount namespace by default, and it is shipped by util-linux [essential]

[Olivier Gayot (ogayot)]

Green build on PPA: https://launchpad.net/~ogayot/+archive/ubuntu/mantic-proposed/+build/26019500

[Dan Bungert (dbungert)]

It's a little bit ceremonial, but I think it sensible to declare a relationship to the util-linux package. Recommends sounds appropriate.

Otherwise LGTM.

[Olivier Gayot (ogayot)]

Hi dbungert,

Thanks for reviewing this patch.

I tried the suggested change (adding util-linux as a Recommends) but it introduces the following lintian error:

E: os-prober: depends-on-essential-package-without-using-version Recommends: util-linux

Thanks,
Olivier

[Olivier Gayot (ogayot)]

Adding updated debdiff that declares Recommends: util-linux (>> 2.37.2).

[Dan Bungert (dbungert)]

Uploaded, thanks!

[Launchpad Janitor (janitor)]

This bug was fixed in the package os-prober - 1.81ubuntu3

---------------
os-prober (1.81ubuntu3) mantic; urgency=medium

  * Replace newns by unshare --mount from util-linux [essential]. This makes
    os-prober run in a private mount namespace, as it was initially intended.
    (LP: #2018271)

 -- Olivier Gayot <email address hidden> Tue, 02 May 2023 09:19:22 +0200