linux-hardening - Isolating abstract sockets

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Message-ID: <Y59qBh9rRDgsIHaj@mailbox.org>
Date:   Sun, 18 Dec 2022 20:29:10 +0100
From:   Stefan Bavendiek <stefan.bavendiek@...lbox.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     linux-hardening@...r.kernel.org
Subject: Isolating abstract sockets

When building userspace application sandboxes, one issue that does not seem trivial to solve is the isolation of abstract sockets.

While most IPC mechanism can be isolated by mechanisms like mount namespaces, abstract sockets are part of the network namespace.
It is possible to isolate abstract sockets by using a new network namespace, however, unprivileged processes can only create a new empty network namespace, which removes network access as well and makes this useless for network clients.

Same linux sandbox projects try to solve this by bridging the existing network interfaces into the new namespace or use something like slirp4netns to archive this, but this does not look like an ideal solution to this problem, especially since sandboxing should reduce the kernel attack surface without introducing more complexity.

Aside from containers using namespaces, sandbox implementations based on seccomp and landlock would also run into the same problem, since landlock only provides file system isolation and seccomp cannot filter the path argument and therefore it can only be used to block new unix domain socket connections completely.

Currently there does not seem to be any way to disable network namespaces in the kernel without also disabling unix domain sockets.

The question is how to solve the issue of abstract socket isolation in a clean and efficient way, possibly even without namespaces.
What would be the ideal way to implement a mechanism to disable abstract sockets either globally or even better, in the context of a process.
And would such a patch have a realistic chance to make it into the kernel?

- Stefan

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