Messages in this thread | | | Date | Sat, 27 Jun 2020 14:23:32 +0200 | From | Christian Brauner <> | Subject | Re: [fork] 11689456e6: ltp.clone302.fail |
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On Sat, Jun 27, 2020 at 04:27:48PM +0800, kernel test robot wrote: > Greeting, > > FYI, we noticed the following commit (built with gcc-9): > > commit: 11689456e6df828b7917a558a36212e68fa9aa69 ("[PATCH 01/17] fork: fold legacy_clone_args_valid() into _do_fork()") > url: https://github.com/0day-ci/linux/commits/Christian-Brauner/arch-remove-do_fork-and-HAVE_COPY_THREAD_TLS/20200623-080105 > base: https://git.kernel.org/cgit/linux/kernel/git/davem/sparc.git master > > in testcase: ltp > with following parameters: > > disk: 1HDD > fs: ext4 > test: syscalls_part1 > > test-description: The LTP testsuite contains a collection of tools for testing the Linux kernel and related features. > test-url: http://linux-test-project.github.io/ > > > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G > > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace): > > > > > If you fix the issue, kindly add following tag > Reported-by: kernel test robot <rong.a.chen@intel.com> > > > <<<test_start>>> > tag=clone302 stime=1593153327 > cmdline="clone302" > contacts="" > analysis=exit > <<<test_output>>> > tst_buffers.c:55: INFO: Test is using guarded buffers > tst_test.c:1247: INFO: Timeout per run is 0h 05m 00s > clone302.c:92: PASS: invalid args: clone3() failed as expected: EFAULT (14) > clone302.c:92: PASS: zero size: clone3() failed as expected: EINVAL (22) > clone302.c:92: PASS: short size: clone3() failed as expected: EINVAL (22) > clone302.c:92: PASS: extra size: clone3() failed as expected: EFAULT (14) > clone302.c:92: PASS: sighand-no-VM: clone3() failed as expected: EINVAL (22) > clone302.c:92: PASS: thread-no-sighand: clone3() failed as expected: EINVAL (22) > clone302.c:92: PASS: fs-newns: clone3() failed as expected: EINVAL (22) > clone302.c:92: PASS: invalid pidfd: clone3() failed as expected: EFAULT (14) > clone302.c:92: PASS: invalid childtid: clone3() failed as expected: EFAULT (14) > clone302.c:88: FAIL: invalid parenttid: clone3() should fail with EFAULT: EINVAL (22)
In short, this is a change in failure behavior for clone3() I did expect and am willing to risk. Here's why in the short form: - clone3() is extremely new - this failed before - setting both CLONE_PIDFD and CLONE_PARENT_SETTID is extremely rare (haven't seen it in any codebases I know that use clone3()) - setting both CLONE_PIDFD and CLONE_PARENT_SETTID __and__ pointing them to the same adress doesn't work (haven't seen it in any codebases I know that use clone3() but see some more notes on that below) - the change makes a special case go away and simplifies multiple call-sites
So a few notes about the test. I did stare at it for a while and was confused why you expect EFAULT to be returned when CLONE_PARENT_SETTID is set to an invalid memory address. Because that doesn't make sense. When the parent tid is written to the memory location for CLONE_PARENT_SETTID we're past the point of no return of process creation, i.e. the return value from put_user() isn't checked and can't be checked anymore so you'd never receive EFAULT for a bogus parent_tid memory address. This is not something new. This has been the case since the introduction of pid namespaces and specifically since commit 30e49c263e36 ("pid namespaces: allow cloning of new namespace").
But then it dawned on me. You're setting CLONE_PIDFD | CLONE_PARENT_SETTID and you're pointing: - args->parent_tid = <invalid-address> - args->pidfd = NULL so the EFAULT you've seen so far in your test-suite has never been for CLONE_PARENT_SETTID but for CLONE_PIDFD since that value is written before the point of no return and consequently put_user() is checked and the EFAULT is surfaced. So independent of that issue here you might want to adapt that test so it really tests what you want. :) (And maybe it's worth documenting on the manpage for clone{3}() that failures for CLONE_PARENT_SETTID and CLONE_CHILD_SETTID are not seen.)
(Also, note that for some reason, args->pidfd and pargs->parent_tid must've ended up pointing to the same address in your test-suite. So my guess is that args->pidfd pointed to garbage which got turned into a useable address after tst_get_bad_addr() returned &invalid_address. Maybe I'm missing something subtle though.)
Christian
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