linux-kernel - Leaking path or inconsistency LSM checking observed in fs/net

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Message-ID: <e6ef53a8-187e-d030-9246-3de2a9a79265@tycho.nsa.gov>
Date:   Tue, 25 Sep 2018 14:44:23 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Tong Zhang <ztong@...edu>, mark@...heh.com, jlbec@...lplan.org,
        keescook@...omium.org, davem@...emloft.net,
        viro@...iv.linux.org.uk, dvlasenk@...hat.com, ccaulfie@...hat.com,
        teigland@...hat.com
Cc:     linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com,
        cluster-devel@...hat.com, linux-security-module@...r.kernel.org,
        Wenbo Shen <shenwenbosmile@...il.com>,
        Paul Moore <paul@...l-moore.com>
Subject: Leaking path or inconsistency LSM checking observed in fs/net

On 09/25/2018 01:27 PM, Tong Zhang wrote:
> Kernel Version: 4.18.5
> 
> Problem Description:
> 
> We found several leaking path or inconsistency LSM design issue in fs/net.
> 
> Currently we can only observe sock creation from kernel and all bind/listen/connect are not sent to LSM.
> So, we think that those net/socket related stuff should all go through LSM check and being audited
> even it is not a user thread or process.
> 
> 
> Here’s an example where we have a check:
> in fs/ocfs2/cluster/tcp.c:2035 o2net_open_listening_sock() a sock is created using sock_create(),
> where a LSM check security_socket_create is called(net/socket.c:1242)
> 
> 
> And where we don’t have a check
> 
> fs/ocfs2/cluster/tcp.c:2052 bind
> fs/ocfs2/cluster/tcp.c:2059 listen
> 
> fs/dlm/lowcomms.c:1264 bind
> fs/dlm/lowcomms.c:1278 listen
> fs/dlm/lowcomms.c:1354 listen
> 
> several places that use kernel_bind/kernel_listen/kernel_connect
> 
> net/socket.c:3231 kernel_bind
> net/socket.c:3237 kernel_listen
> net/socket.c:3286 kernel_connect

That's intentional.  LSM isn't trying to mediate kernel-internal 
operations, and we do not want to apply permission checks against the 
credentials of the current userspace process for such operations.  ocfs2 
should likely be using sock_create_kern.