netdev - Re: [BUG] kernel stack corruption during/after Netlabel error

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Message-ID: <4d73f839-7a86-6edc-b44b-e296bd5947c2@schaufler-ca.com>
Date:   Wed, 29 Nov 2017 16:22:41 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     James Morris <james.l.morris@...cle.com>,
        Paul Moore <paul@...l-moore.com>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     netdev@...r.kernel.org, Stephen Smalley <sds@...ho.nsa.gov>,
        selinux@...ho.nsa.gov, LSM <linux-security-module@...r.kernel.org>
Subject: Re: [BUG] kernel stack corruption during/after Netlabel error

On 11/29/2017 2:26 AM, James Morris wrote:
> I'm seeing a kernel stack corruption bug (detected via gcc) when running 
> the SELinux testsuite on a 4.15-rc1 kernel, in the 2nd inet_socket test:
>
> https://github.com/SELinuxProject/selinux-testsuite/blob/master/tests/inet_socket/test
>
>   # Verify that unauthorized client cannot communicate with the server.
>   $result = system
>   "runcon -t test_inet_bad_client_t -- $basedir/client stream 127.0.0.1 65535 2>&1";
>
> This correctlly causes an access control error in the Netlabel code, and 
> the bug seems to be triggered during the ICMP send:
>
> ...<SNIP>...
>
> This is mostly reliable, and I'm only seeing it on bare metal (not in a 
> virtualbox vm).
>
> The SELinux skb parse error at the start only sometimes appears, and 
> looking at the code, I suspect some kind of memory corruption being the 
> cause at that point (basic packet header checks).
>
> I bisected the bug down to the following change:
>
> commit bffa72cf7f9df842f0016ba03586039296b4caaf
> Author: Eric Dumazet <edumazet@...gle.com>
> Date:   Tue Sep 19 05:14:24 2017 -0700
>
>     net: sk_buff rbnode reorg
>     ...
>
>
> Anyone else able to reproduce this, or have any ideas on what's happening?

I have also bisected a problem to this change. I do not have a trace
because the problem manifests as a hard system hang without a trace
being presented. The issue arises when Smack attempts to relabel a TCP
socket using netlbl_sock_setattr().

I see that there is a proposed fix later in the thread, but I don't see
the patch. Could you send it to me, so I can try it on my problem?

Thank you.

>
>
>
> - James