linux-kernel - Re: PROBLEM: oops spew with Linux 5.1.5 (NFS regression?)

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Date:   Mon, 3 Jun 2019 14:09:41 -0400
From:   Nick Bowler <nbowler@...conx.ca>
To:     Olga Kornievskaia <aglo@...ch.edu>
Cc:     Trond Myklebust <trondmy@...merspace.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Olga.Kornievskaia@...app.com" <Olga.Kornievskaia@...app.com>
Subject: Re: PROBLEM: oops spew with Linux 5.1.5 (NFS regression?)

On 2019-06-03, Nick Bowler <nbowler@...conx.ca> wrote:
> On 2019-05-29, Olga Kornievskaia <aglo@...ch.edu> wrote:
>> On Wed, May 29, 2019 at 1:14 PM Trond Myklebust <trondmy@...merspace.com>
>>> OK, I think this is the same problem that Olga was seeing (Cced), and
>>> it looks like I missed the use-after-free issue when the server returns
>>> a credential error when she asked.
>>
>> I think this is actually different than what I encountered for the
>> umount case but the trigger is the same -- failing validation.
>>
>> I tried to reproduce Nick's oops on 5.2-rc but haven't been able to
>> (but I'm not confident I produced the right trigger conditions. will
>> try 5.1).
>
> OK, I think I found something that triggers this fault.  This happens
> when certain local users try to stat a file or directory on an nfs
> mount.  Presumably these UIDs do not have appropriate permissions on
> the server but I'm not sure exactly (I do not control the server).
>
> I can reproduce the oops with a command like this:
>
>   # su -s/bin/sh -c 'stat /path/to/nfs/file' problematic_user
>
> which oopes every time (and SIGKILLs the stat command).   (I have not yet
> rebooted since the original report or tried with Trond's patch applied.
> I will do that next, and also try 5.1.6).

OK, armed with this reproducer I can confirm that the issue is still
present in 5.1.6, and that applying Trond's patch on top of 5.1.6
appears to fix the problem.

Thanks,
  Nick