linux-kernel - Re: seccomp ptrace selftest failures with 4.4-stable [Was: Re: LTS testing with latest kselftests

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Message-ID: <20170624044343.GC10973@kroah.com>
Date:   Sat, 24 Jun 2017 06:43:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, Shuah Khan <shuah@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Brian Norris <computersforpeace@...il.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Shuah Khan <shuahkh@....samsung.com>
Subject: Re: seccomp ptrace selftest failures with 4.4-stable [Was: Re: LTS
 testing with latest kselftests - some failures]

On Thu, Jun 22, 2017 at 07:40:49PM -0700, Andy Lutomirski wrote:
> Greg, for context, the issue here is that we made what was arguably a
> design error in seccomp's interaction with ptrace.  After determining
> that fixing it solved a bunch of problems and didn't break any user
> programs, we fixed it.  There might be new code that relies on the fix
> being present in the sense that it would be insecure without the fix.
> 
> The problem is that the fix is moderately intrusive and doesn't seem
> like a great candidate for backporting, although we could plausibly do
> it.

That's fine, not all bugfixes that tests are created to find, should be
backported.  That's up to the stable maintainers, or someone who has a
device/vendor tree based on that kernel if they want to do that or not.

That has nothing to do with the fact that the test should fail or
gracefully degrade.  Tests should fail if the action that they are
testing fails.  They should degrade and not run if the _feature_ they
are testing is not present.

Yes, sometimes this is hard, like with the seccomp stuff, and will not
always work, but that's the rule for our userspace api independant of
any testing framework or code.

Look at xfstests, no one gets mad when it adds a new test that old
kernels fail at.  It's up to someone else to either backport the kernel
change, if they want it fixed in an old kernel, not to have xfstests
just not run it at all!  There's nothing different here either.

thanks,

greg k-h