netdev - RDS: Can RDS sockets from different network namespace bind to the same address?

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Message-ID: <MWHPR2201MB107202E590B041A3B1091FC0D0779@MWHPR2201MB1072.namprd22.prod.outlook.com>
Date:   Thu, 16 Dec 2021 01:32:24 +0000
From:   "Liu, Congyu" <liu3101@...due.edu>
To:     "rds-devel@....oracle.com" <rds-devel@....oracle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "santosh.shilimkar@...cle.com" <santosh.shilimkar@...cle.com>
Subject: RDS: Can RDS sockets from different network namespace bind to the
 same address?

Hi,

(Resend this email in plain text in case the previous one was spammed. Sorry for the trouble caused.)

I am writing to ask about if two RDS sockets from different network namespaces can bind to the same address.

I am doing research on container security. Recently our tool produced a simple test case with confusing test result: there are two network namespaces A and B. Both A and B has a tun device, and these two tun devices have the same IPv4 address. In namespace A a RDS socket is created and binds it to namespace A's tun device. It works. But then in namespace B the other RDS socket is created and binds it to namespace B's tun device, it fails with error code EADDRINUSE. Is this considered as expected behavior? 

Thanks,
Congyu