[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 [off-list ref]
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

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