linux-kernel - Can Not Send Netlink Messages with Unshare(CLONE

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Message-ID: <CAKdx3izLgNJO+5ye4twe0+CFMcUBrFUa+-NdLN6VKKWQ76YiLA@mail.gmail.com>
Date:   Thu, 17 Nov 2022 15:55:21 +0800
From:   Hang An <anhang610@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: Can Not Send Netlink Messages with Unshare(CLONE_NEWNET)

Hi,
A process can not send netlink messages(errno is ECONNREFUSED) after
running unshare(CLONE_NEWNET).

Part of the call stack when process failed:
netlink_sendmsg
netlink_unicast
netlink_getsockbyportid
netlink_lookup(return NULL)

The corresponding pseudocode is shown below:
unshare(CLONE_NEWNET) ;
res_socket = syscall(__NR_socket, 0x10ul, 3ul, 8);
syscall(__NR_sendmsg, res_socket, msghdr, 0ul);

I can't understand this situation. Is this a bug or special design?

Thanks.