Re: [PATCH] apparmor: Upgrade ABI version to 4.0, explicitly enable user namespace creation

On Mon, 12 Jan 2026 08:11:44 -0700 Andrea Bolognani wrote:

[adding libvirt devel list]

On Sat, Jan 10, 2026 at 04:14:30PM +0100, Stefano Brivio wrote:

...

In the 3.0 AppArmor ABI version we currently use, user namespace rules are not supported, and, as long as we load confined profiles, those implicitly allow creation of user namespaces.

However, ABI version 4.0 introduces rules for user namespaces, and if we don't specify any, we can't create user namespaces, see:

https://gitlab.com/apparmor/apparmor/-/wikis/unprivileged_userns_restriction

This wouldn't affect us in general, given that we're using the 3.0 ABI, but libvirt's policy uses 4.0 instead, and if our abstractions are used from there, no matter what ABI policy version we declare, rules for user namespace creation now match ABI policy version 4.0.

AFAICT libvirt's policy doesn't explicitly declares any ABI version, so how does that work? Is the most recent one being used in that case?

Oh, right, I forgot to mention that this is implicit from including abstraction/base in libvirt's policy, which uses 4.0 on all the current versions of AppArmor-enabled distributions I checked (Debian, including stable/trixie, Ubuntu, openSUSE).

Assuming that's the case, how far back will that result in ABI 4.0 being the effective one? It looks like Debian only got AppArmor 4+ in March of last year.

Given that it's bound to the version from abstraction/base, the only risk I see is that passt might now ship a policy with an ABI version that's too new for the distribution at hand. But ABI 4.0 has been around for more than two years now, so I don't really see a problem.

Do we want to make the ABI version explicit in libvirt's policy? If so, should we stick with 3.0 for maximum compatibility?

I wouldn't make it explicit. Yes, sticking to 3.0 would have avoided this issue and resulted in better compatibility overall but would cause even more problems if you ever need to switch "back" to 4.0 at some point in time. I think that using the version from abstraction/base as libvirt does is actually a more convenient and compatible approach in general. We didn't do that in passt's policy because the rules included there are too broad, but given that libvirtd's policy already includes it, I'd suggest to keep it that way.

...

As a result, when libvirtd runs as root, and its profile includes passt's abstraction, cf. commit 66769c2de825 ("apparmor: Workaround for unconfined libvirtd when triggered by unprivileged user"), passt can't detach user namespaces and will fail to start, as reported by Niklas:

ERROR internal error: Child process (passt --one-off --socket /run/libvirt/qemu/passt/1-haos-net0.socket --pid /run/libvirt/qemu/passt/1-haos-net0-passt.pid --tcp-ports 8123) unexpected exit status 1: Multiple interfaces with IPv6 routes, picked first UNIX domain socket bound at /run/libvirt/qemu/passt/1-haos-net0.socket Couldn't create user namespace: Permission denied

This isn't a problem with libvirtd running as regular user, because in that case, as a workaround, passt currently runs under its own profile, not as a libvirtd subprofile (see commit referenced above).

Given that ABI 4.0 has been around for a while, being introduced in July 2023, finally take the step to upgrade to it and explicitly enable user namespace creation.

No further changes are needed in the existing policies to match new features introduced in AppArmor 4.0.

Reported-by: Niklas Edmundsson Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1124801 Signed-off-by: Stefano Brivio --- contrib/apparmor/abstractions/passt | 3 ++- contrib/apparmor/abstractions/pasta | 2 +- contrib/apparmor/usr.bin.passt | 2 +- contrib/apparmor/usr.bin.passt-repair | 2 +- contrib/apparmor/usr.bin.pasta | 2 +- 5 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/contrib/apparmor/abstractions/passt b/contrib/apparmor/abstractions/passt index 25b2ea8..0ffadaf 100644 --- a/contrib/apparmor/abstractions/passt +++ b/contrib/apparmor/abstractions/passt @@ -11,7 +11,7 @@ # Copyright (c) 2022 Red Hat GmbH # Author: Stefano Brivio

- abi , + abi ,

include

@@ -24,6 +24,7 @@ capability setpcap, capability net_admin, capability sys_ptrace, + userns,

/ r, # isolate_prefork(), isolation.c mount options=(rw, runbindable) -> /, diff --git a/contrib/apparmor/abstractions/pasta b/contrib/apparmor/abstractions/pasta index 9f73bee..251d4a2 100644 --- a/contrib/apparmor/abstractions/pasta +++ b/contrib/apparmor/abstractions/pasta @@ -11,7 +11,7 @@ # Copyright (c) 2022 Red Hat GmbH # Author: Stefano Brivio

- abi , + abi ,

include

diff --git a/contrib/apparmor/usr.bin.passt b/contrib/apparmor/usr.bin.passt index 62a4514..c123a86 100644 --- a/contrib/apparmor/usr.bin.passt +++ b/contrib/apparmor/usr.bin.passt @@ -11,7 +11,7 @@ # Copyright (c) 2022 Red Hat GmbH # Author: Stefano Brivio

-abi , +abi ,

include

diff --git a/contrib/apparmor/usr.bin.passt-repair b/contrib/apparmor/usr.bin.passt-repair index 901189d..23ff1ce 100644 --- a/contrib/apparmor/usr.bin.passt-repair +++ b/contrib/apparmor/usr.bin.passt-repair @@ -11,7 +11,7 @@ # Copyright (c) 2025 Red Hat GmbH # Author: Stefano Brivio

-abi , +abi ,

#include

diff --git a/contrib/apparmor/usr.bin.pasta b/contrib/apparmor/usr.bin.pasta index 2483968..56b5024 100644 --- a/contrib/apparmor/usr.bin.pasta +++ b/contrib/apparmor/usr.bin.pasta @@ -11,7 +11,7 @@ # Copyright (c) 2022 Red Hat GmbH # Author: Stefano Brivio

-abi , +abi ,

include

-- 2.43.0

-- Stefano