linux-kernel - Re: Linux 5.0-rc2 seccomp_bpf user_notification

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Message-ID: <20190117004416.GA17449@cisco>
Date:   Wed, 16 Jan 2019 17:44:16 -0700
From:   Tycho Andersen <tycho@...ho.ws>
To:     Kees Cook <keescook@...omium.org>
Cc:     shuah <shuah@...nel.org>, James Morris <jmorris@...ei.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: Linux 5.0-rc2 seccomp_bpf user_notification_basic test hangs

On Wed, Jan 16, 2019 at 04:30:26PM -0800, Kees Cook wrote:
> On Wed, Jan 16, 2019 at 4:01 PM shuah <shuah@...nel.org> wrote:
> >
> > Hi Kees and James,
> >
> > seccomp_bpf test hangs right after the following test passes
> > with EBUSY. Please see log at the end.
> >
> > /* Installing a second listener in the chain should EBUSY */
> >          EXPECT_EQ(user_trap_syscall(__NR_getpid,
> >                                      SECCOMP_FILTER_FLAG_NEW_LISTENER),
> >                    -1);
> >          EXPECT_EQ(errno, EBUSY);
> >
> >
> > The user_notification_basic test starts running I assume and then
> > the hang.
> >
> > The only commit I see that could be suspect is the following as
> > it talks about adding SECCOMP_RET_USER_NOTIF
> >
> > commit d9a7fa67b4bfe6ce93ee9aab23ae2e7ca0763e84
> > Merge: f218a29c25ad 55b8cbe470d1
> > Author: Linus Torvalds <torvalds@...ux-foundation.org>
> > Date:   Wed Jan 2 09:48:13 2019 -0800
> >
> >      Merge branch 'next-seccomp' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security
> >
> >      Pull seccomp updates from James Morris:
> >
> >       - Add SECCOMP_RET_USER_NOTIF
> >
> >       - seccomp fixes for sparse warnings and s390 build (Tycho)
> >
> >      * 'next-seccomp' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
> >        seccomp, s390: fix build for syscall type change
> >        seccomp: fix poor type promotion
> >        samples: add an example of seccomp user trap
> >        seccomp: add a return code to trap to userspace
> >        seccomp: switch system call argument type to void *
> >        seccomp: hoist struct seccomp_data recalculation higher
> >
> >
> > Any ideas on how to proceed? Here is the log. The following
> > reproduces the problem.
> >
> > make -C tools/testing/selftests/seccomp/ run_tests
> >
> >
> > seccomp_bpf.c:2947:global.get_metadata:Expected 0 (0) ==
> > seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_LOG, &prog)
> > (18446744073709551615)
> > seccomp_bpf.c:2959:global.get_metadata:Expected 1 (1) == read(pipefd[0],
> > &buf, 1) (0)
> > global.get_metadata: Test terminated by assertion
> > [     FAIL ] global.get_metadata
> > [ RUN      ] global.user_notification_basic
> > seccomp_bpf.c:3036:global.user_notification_basic:Expected 0 (0) ==
> > WEXITSTATUS(status) (1)
> > seccomp_bpf.c:3039:global.user_notification_basic:Expected
> > seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog) (18446744073709551615) == 0 (0)
> > seccomp_bpf.c:3040:global.user_notification_basic:Expected
> > seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog) (18446744073709551615) == 0 (0)
> > seccomp_bpf.c:3041:global.user_notification_basic:Expected
> > seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog) (18446744073709551615) == 0 (0)
> > seccomp_bpf.c:3042:global.user_notification_basic:Expected
> > seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog) (18446744073709551615) == 0 (0)
> > seccomp_bpf.c:3047:global.user_notification_basic:Expected listener
> > (18446744073709551615) >= 0 (0)
> > seccomp_bpf.c:3053:global.user_notification_basic:Expected errno (13) ==
> > EBUSY (16)
> 
> Looks like the test is unfriendly when running the current selftest on
> an old kernel version. A quick look seems like it's missing some
> ASSERT_* cases where EXPECT_* is used. I'll send a patch.

ASSERT will kill the test case though right? I thought we were
supposed to use EXPECT when we wanted it to keep going. In particular,
it looks like in the get_metadata test, we should be using expect
instead of assert in some places, so we can get to the write() that
does the synchronization. Something like,

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 067cb4607d6c..4d2508af2483 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -2943,11 +2943,11 @@ TEST(get_metadata)
 		};
 
 		/* one with log, one without */
-		ASSERT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER,
+		EXPECT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER,
 				     SECCOMP_FILTER_FLAG_LOG, &prog));
-		ASSERT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog));
+		EXPECT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog));
 
-		ASSERT_EQ(0, close(pipefd[0]));
+		EXPECT_EQ(0, close(pipefd[0]));
 		ASSERT_EQ(1, write(pipefd[1], "1", 1));
 		ASSERT_EQ(0, close(pipefd[1]));
 

But also, is running new tests on an old kernel expected to work? I
didn't know that :).

Tycho