selftest/pidfd: add test for thread-group leader pidfd open for thread

Verify that we report ENOENT when userspace tries to create a
thread-group leader pidfd for a thread pidfd that isn't a thread-group
leader.

Link: https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-4-a123b6ed6716@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/tools/testing/selftests/pidfd/pidfd_info_test.c b/tools/testing/selftests/pidfd/pidfd_info_test.c
index accfd6bdc539e57173bf8fbb763eff687321168e..a0eb6e81eaa26d1d44b94546397b1dd6dead4b29 100644 (file)
--- a/tools/testing/selftests/pidfd/pidfd_info_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_info_test.c
@@ -299,6 +299,7 @@ TEST_F(pidfd_info, thread_group)
        /* Opening a thread as a thread-group leader must fail. */
        pidfd_thread = sys_pidfd_open(pid_thread, 0);
        ASSERT_LT(pidfd_thread, 0);
+       ASSERT_EQ(errno, ENOENT);
 
        /* Opening a thread as a PIDFD_THREAD must succeed. */
        pidfd_thread = sys_pidfd_open(pid_thread, PIDFD_THREAD);