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Date:   Thu, 7 Nov 2019 15:33:37 -0800
From:   Brendan Higgins <brendanhiggins@google.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     shuah@kernel.org, john.johansen@canonical.com, jmorris@namei.org,
        serge@hallyn.com, alan.maguire@oracle.com, yzaikin@google.com,
        davidgow@google.com, mcgrof@kernel.org, tytso@mit.edu,
        linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org, kunit-dev@googlegroups.com,
        linux-kselftest@vger.kernel.org,
        Mike Salvatore <mike.salvatore@canonical.com>
Subject: Re: [PATCH linux-kselftest/test v2] apparmor: add AppArmor KUnit
 tests for policy unpack
Message-ID: <20191107233337.GA191231@google.com>
References: <20191106004329.16991-1-brendanhiggins@google.com>
 <201911060916.AC9E14B@keescook>
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On Wed, Nov 06, 2019 at 09:18:27AM -0800, Kees Cook wrote:
> On Tue, Nov 05, 2019 at 04:43:29PM -0800, Brendan Higgins wrote:
> > From: Mike Salvatore <mike.salvatore@canonical.com>
> > 
> > Add KUnit tests to test AppArmor unpacking of userspace policies.
> > AppArmor uses a serialized binary format for loading policies. To find
> > policy format documentation see
> > Documentation/admin-guide/LSM/apparmor.rst.
> > 
> > In order to write the tests against the policy unpacking code, some
> > static functions needed to be exposed for testing purposes. One of the
> > goals of this patch is to establish a pattern for which testing these
> > kinds of functions should be done in the future.
> > 
> > Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
> > Signed-off-by: Mike Salvatore <mike.salvatore@canonical.com>
> > ---
> >  security/apparmor/Kconfig              |  16 +
> >  security/apparmor/policy_unpack.c      |   4 +
> >  security/apparmor/policy_unpack_test.c | 607 +++++++++++++++++++++++++
> >  3 files changed, 627 insertions(+)
> >  create mode 100644 security/apparmor/policy_unpack_test.c
> > 
> > diff --git a/security/apparmor/Kconfig b/security/apparmor/Kconfig
> > index d8b1a360a6368..78a33ccac2574 100644
> > --- a/security/apparmor/Kconfig
> > +++ b/security/apparmor/Kconfig
> > @@ -66,3 +66,19 @@ config SECURITY_APPARMOR_DEBUG_MESSAGES
> >  	  Set the default value of the apparmor.debug kernel parameter.
> >  	  When enabled, various debug messages will be logged to
> >  	  the kernel message buffer.
> > +
> > +config SECURITY_APPARMOR_KUNIT_TEST
> > +	bool "Build KUnit tests for policy_unpack.c"
> > +	depends on KUNIT && SECURITY_APPARMOR
> > +	help
> > +	  This builds the AppArmor KUnit tests.
> > +
> > +	  KUnit tests run during boot and output the results to the debug log
> > +	  in TAP format (http://testanything.org/). Only useful for kernel devs
> > +	  running KUnit test harness and are not for inclusion into a
> > +	  production build.
> > +
> > +	  For more information on KUnit and unit tests in general please refer
> > +	  to the KUnit documentation in Documentation/dev-tools/kunit/.
> > +
> > +	  If unsure, say N.
> > diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
> > index 8cfc9493eefc7..37c1dd3178fc0 100644
> > --- a/security/apparmor/policy_unpack.c
> > +++ b/security/apparmor/policy_unpack.c
> > @@ -1120,3 +1120,7 @@ int aa_unpack(struct aa_loaddata *udata, struct list_head *lh,
> >  
> >  	return error;
> >  }
> > +
> > +#ifdef CONFIG_SECURITY_APPARMOR_KUNIT_TEST
> > +#include "policy_unpack_test.c"
> > +#endif /* CONFIG_SECURITY_APPARMOR_KUNIT_TEST */
> 
> To make this even LESS intrusive, the ifdefs could live in ..._test.c.

Less intrusive, yes, but I think I actually like the ifdef here; it
makes it clear from the source that the test is only a part of the build
when configured to do so. Nevertheless, I will change it if anyone feels
strongly about it.

> Also, while I *think* the kernel build system will correctly track this
> dependency, can you double-check that changes to ..._test.c correctly
> trigger a recompile of policy_unpack.c?

Yep, just verified, first I ran the tests and everything passed. Then I
applied the following diff:

diff --git a/security/apparmor/policy_unpack_test.c b/security/apparmor/policy_unpack_test.c
index 533137f45361c..e1b0670dbdc27 100644
--- a/security/apparmor/policy_unpack_test.c
+++ b/security/apparmor/policy_unpack_test.c
@@ -161,7 +161,7 @@ static void policy_unpack_test_unpack_array_with_name(struct kunit *test)
 
 	array_size = unpack_array(puf->e, name);
 
-	KUNIT_EXPECT_EQ(test, array_size, (u16)TEST_ARRAY_SIZE);
+	KUNIT_EXPECT_EQ(test, array_size + 1, (u16)TEST_ARRAY_SIZE);
 	KUNIT_EXPECT_PTR_EQ(test, puf->e->pos,
 		puf->e->start + TEST_ARRAY_BUF_OFFSET + sizeof(u16) + 1);
 }

and reran the tests (to trigger an incremental build) and the test
failed as expected indicating that the dependency is properly tracked.

Cheers!