Subject: Re: [PATCH v3 4/6] selftest/Landlock: pthread_kill(3) tests

From: Mickaël Salaün <[email-masked]>
Date: Mon, 26 Aug 2024 14:40:39 +0200

On Tue, Aug 20, 2024 at 05:57:08PM +0200, Mickaël Salaün wrote:
> Please make sure all subject's prefixes are correct, there is two errors
> in the prefix and the description can be made more consistent with other
> patches, something like this: "selftests/landlock: Add
> signal_scoping_threads test"
> 
> On Thu, Aug 15, 2024 at 12:29:23PM -0600, Tahera Fahimi wrote:
> > This patch expands the signal scoping tests with pthread_kill(3)
> > It tests if an scoped thread can send signal to a process in
> > the same scoped domain, or a non-sandboxed thread.
> > 
> > Signed-off-by: Tahera Fahimi <[email-masked]>
> > ---
> >  .../selftests/landlock/scoped_signal_test.c   | 29 +++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/landlock/scoped_signal_test.c b/tools/testing/selftests/landlock/scoped_signal_test.c
> > index 92958c6266ca..2edba1e6cd82 100644
> > --- a/tools/testing/selftests/landlock/scoped_signal_test.c
> > +++ b/tools/testing/selftests/landlock/scoped_signal_test.c
> > @@ -10,6 +10,7 @@
> >  #include <errno.h>
> >  #include <fcntl.h>
> >  #include <linux/landlock.h>
> > +#include <pthread.h>
> >  #include <signal.h>
> >  #include <sys/prctl.h>
> >  #include <sys/types.h>
> > @@ -18,6 +19,7 @@
> >  
> >  #include "common.h"
> >  
> > +#define DEFAULT_THREAD_RUNTIME 0.001
> >  static sig_atomic_t signaled;
> >  
> >  static void create_signal_domain(struct __test_metadata *const _metadata)
> > @@ -299,4 +301,31 @@ TEST_F(signal_scoping, test_signal)
> >  		_metadata->exit_code = KSFT_FAIL;
> >  }
> >  
> > +static void *thread_func(void *arg)
> > +{
> > +	sleep(DEFAULT_THREAD_RUNTIME);
> 
> Using sleep() may make this test flaky.  It needs to be removed and the
> test should work the same.
> 
> > +	return NULL;
> > +}
> > +
> > +TEST(signal_scoping_threads)
> > +{
> > +	pthread_t no_sandbox_thread, scoped_thread;
> > +	int err;
> > +
> > +	ASSERT_EQ(0,
> > +		  pthread_create(&no_sandbox_thread, NULL, thread_func, NULL));
> > +	create_signal_domain(_metadata);
> > +	ASSERT_EQ(0, pthread_create(&scoped_thread, NULL, thread_func, NULL));
> > +
> > +	/* Send signal to threads */
> > +	err = pthread_kill(no_sandbox_thread, 0);
> > +	ASSERT_EQ(EPERM, err);

Sometime the test failed because err == 0, I guess it's because I
removed the call to sleep(), but this just highlight a race condition in
the code anyway.  We would need a synchronization primitive to make sure
the thread is still alive, something like the pipe read/write.

> > +
> > +	err = pthread_kill(scoped_thread, 0);
> > +	ASSERT_EQ(0, err);
> > +
> > +	ASSERT_EQ(0, pthread_join(scoped_thread, NULL));
> > +	ASSERT_EQ(0, pthread_join(no_sandbox_thread, NULL));
> > +}
> > +
> >  TEST_HARNESS_MAIN
> > -- 
> > 2.34.1
> > 
> >