On Mon, Apr 29, 2024 at 03:09:26PM +0200, Mickaël Salaün wrote:
> Fix a race condition when running several FIXTURE_TEARDOWN() managing
> the same resource. This fixes a race condition in the Landlock file
> system tests when creating or unmounting the same directory.
>
> Using clone3() with CLONE_VFORK guarantees that the child and grandchild
> test processes are sequentially scheduled. This is implemented with a
> new clone3_vfork() helper replacing the fork() call.
>
> This avoids triggering this error in __wait_for_test():
> Test ended in some other way [127]
>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Günther Noack <gnoack@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Cc: Shuah Khan <shuah@xxxxxxxxxx>
> Cc: Will Drewry <wad@xxxxxxxxxxxx>
> Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
> Link: https://lore.kernel.org/r/20240429130931.2394118-5-mic@xxxxxxxxxxx
> ---
> tools/testing/selftests/kselftest_harness.h | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
> index 55699a762c45..9f04638707ae 100644
> --- a/tools/testing/selftests/kselftest_harness.h
> +++ b/tools/testing/selftests/kselftest_harness.h
> @@ -66,6 +66,8 @@
> #include <sys/wait.h>
> #include <unistd.h>
> #include <setjmp.h>
> +#include <syscall.h>
> +#include <linux/sched.h>
>
> #include "kselftest.h"
>
> @@ -80,6 +82,17 @@
> # define TH_LOG_ENABLED 1
> #endif
>
> +/* Wait for the child process to end but without sharing memory mapping. */
> +static pid_t __attribute__((__unused__)) clone3_vfork(void)
Why "unused"?
> +{
> + struct clone_args args = {
> + .flags = CLONE_VFORK,
> + .exit_signal = SIGCHLD,
> + };
> +
> + return syscall(__NR_clone3, &args, sizeof(args));
> +}
> +
> /**
> * TH_LOG()
> *
> @@ -1183,7 +1196,7 @@ void __run_test(struct __fixture_metadata *f,
> fflush(stdout);
> fflush(stderr);
>
> - t->pid = fork();
> + t->pid = clone3_vfork();
> if (t->pid < 0) {
> ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
> t->exit_code = KSFT_FAIL;
Regardless, yup, looks good.
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook
