Re: Linux 5.0-rc2 seccomp_bpf user_notification_basic test hangs

[shuah <shuah@kernel.org>]

On 1/16/19 5:44 PM, Tycho Andersen wrote:
> On Wed, Jan 16, 2019 at 04:30:26PM -0800, Kees Cook wrote:
>> On Wed, Jan 16, 2019 at 4:01 PM shuah <shuah@kernel.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@linux-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 :).
> 

I am running Linux 5.0-rc2 and not an older kernel.

thanks,
-- Shuah