From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
Date: Sun, 9 Mar 2025 14:28:13 +0100
> Add SO_PEERCGROUPID which allows to get cgroup_id
> for a socket.
This looks useless for SOCK_DGRAM as the server can't have a
peer for clients to send() or connect() (see unix_may_send()).
Is there any reason to support only the connect()ed peer ?
It seems the uAPI group expects to retrieve data per message
as SCM_CGROUPID.
>
> 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.
[...]
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 2b2c0036efc9..3455f38f033d 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -901,6 +901,66 @@ static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
> #define unix_show_fdinfo NULL
> #endif
>
> +static int unix_getsockopt(struct socket *sock, int level, int optname,
> + char __user *optval, int __user *optlen)
> +{
> + struct sock *sk = sock->sk;
> +
> + union {
> + int val;
> + u64 val64;
As Willem pointed out, simply use val64 only.
> + } v;
> +
> + int lv = sizeof(int);
> + int len;
> +
> + if (level != SOL_SOCKET)
> + return -ENOPROTOOPT;
> +
> + if (get_user(len, optlen))
> + return -EFAULT;
> +
> + if (len < 0)
> + return -EINVAL;
> +
> + memset(&v, 0, sizeof(v));
> +
> + switch (optname) {
> +#ifdef CONFIG_SOCK_CGROUP_DATA
> + case SO_PEERCGROUPID:
> + {
> + struct sock *peer;
> + u64 peer_cgroup_id = 0;
Same remarks in patch 1, reverse xmas tree order, and no
initialisation needed.
> +
> + lv = sizeof(u64);
> + if (len < lv)
> + return -EINVAL;
> +
> + peer = unix_peer_get(sk);
> + if (!peer)
> + return -ENODATA;
> +
> + peer_cgroup_id = cgroup_id(sock_cgroup_ptr(&peer->sk_cgrp_data));
> + sock_put(peer);
> +
> + v.val64 = peer_cgroup_id;
> + break;
> + }
> +#endif
> + default:
> + return -ENOPROTOOPT;
> + }
> +
> + if (len > lv)
> + len = lv;
> + if (copy_to_user(optval, &v, len))
> + return -EFAULT;
> + if (put_user(len, optlen))
> + return -EFAULT;
> +
> + return 0;
> +}
> +
