linux-kernel - Re: Allow ioctl TUNSETIFF without CAP_NET

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Message-ID: <Zumq_CxJZ9hWuJIk@mini-arch>
Date: Tue, 17 Sep 2024 09:14:52 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Zach Walton <me@...h.us>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	linux-kernel@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org
Subject: Re: Allow ioctl TUNSETIFF without CAP_NET_ADMIN via seccomp?

On 09/17, Zach Walton wrote:
> Thanks, I think this might have been a misunderstanding on my part;
> seccomp is meant to restrict, not expand, permissions. I spent some
> time looking for prior art and see nothing like it.
> 
> I will look into alternatives like AppArmor/eBPF. Appreciate the response.

There is a bit of "expand capabilities" prior art in the bind cgroup hooks:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/include/linux/bpf.h#n2075

The BPF program can return special value to ask kernel to not apply
CAP_NET_BIND_SERVICE. But this eBPF hook, not a seccomp..