Re: [linus:master] [selftests/memfd] 11f75a0144: kernel-selftests.memfd.run_fuse_test.sh.fail

[Daniel Verkamp]

On Fri, Mar 31, 2023 at 8:05 AM kernel test robot <yujie.liu@xxxxxxxxx> wrote:
>
> Hello,
>
> kernel test robot noticed kernel-selftests.memfd.run_fuse_test.sh.fail due to commit (built with gcc-11):
>
> commit: 11f75a01448f1b7a739e75dbd8f17b844fcfc510 ("selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
> in testcase: kernel-selftests
> version: kernel-selftests-x86_64-d4cf28ee-1_20230110
> with following parameters:
>
>         group: group-02
>
> test-description: The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel.
> test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
>
> on test machine: 4 threads Intel(R) Xeon(R) CPU E3-1225 v5 @ 3.30GHz (Skylake) with 16G memory
>
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>
>
> # selftests: memfd: run_fuse_test.sh
> # Aborted
> not ok 2 selftests: memfd: run_fuse_test.sh # exit=134
>
> $ ./run_fuse_test.sh
> opening: ./mnt/memfd
> 8 != 40 = GET_SEALS(4)
> Aborted

Hi Jeff,

I think this is caused by test_sysctl() in memfd_test, which sets
/proc/sys/vm/memfd_noexec to a non-zero value and does not restore it
at the end of the test. If fuse_test runs after that, it will
unexpectedly get F_SEAL_EXEC in its memfd seals in addition to the
F_SEAL_WRITE that it intended to add.

I'm not sure how kernel selftests normally perform cleanup (e.g. an
atexit() hook to make sure it cleans up if a test fails?), but at
least we should probably set /proc/sys/vm/memfd_noexec back to its
original value after test_sysctl().

Thanks,
-- Daniel