Re: [PATCH net-next 0/4] Add getsockopt(SO_PEERCGROUPID) and fdinfo API to retreive socket's peer cgroup id

[Tejun Heo <tj@kernel.org>]

On Sun, Mar 09, 2025 at 02:28:11PM +0100, Alexander Mikhalitsyn wrote:
> 1. Add socket cgroup id and socket's peer cgroup id in socket's fdinfo
> 2. Add SO_PEERCGROUPID which allows to retrieve socket's peer cgroup id
> 3. Add SO_PEERCGROUPID kselftest
> 
> Generally speaking, this API allows race-free resolution of socket's peer cgroup id.
> Currently, to do that SCM_CREDENTIALS/SCM_PIDFD -> pid -> /proc/<pid>/cgroup sequence
> is used which is racy.
> 
> As we don't add any new state to the socket itself there is no potential locking issues
> or performance problems. We use already existing sk->sk_cgrp_data.
> 
> We already have analogical interfaces to retrieve this
> information:
> - inet_diag: INET_DIAG_CGROUP_ID
> - eBPF: bpf_sk_cgroup_id
> 
> Having getsockopt() interface makes sense for many applications, because using eBPF is
> not always an option, while inet_diag has obvious complexety and performance drawbacks
> if we only want to get this specific info for one specific socket.
> 
> Idea comes from UAPI kernel group:
> https://uapi-group.org/kernel-features/
> 
> Huge thanks to Christian Brauner, Lennart Poettering and Luca Boccassi for proposing
> and exchanging ideas about this.
> 
> Git tree:
> https://github.com/mihalicyn/linux/tree/so_peercgroupid

From cgroup POV:

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun