[LTP] [PATCH v3] Add unshare(CLONE_NEWPID) test

[lufei]

Test unshare(CLONE_NEWPID) to make first child in new PID namespce get
pid 1.

Signed-off-by: lufei <lufei@uniontech.com>
---
 runtest/syscalls                              |  1 +
 testcases/kernel/syscalls/unshare/.gitignore  |  1 +
 testcases/kernel/syscalls/unshare/unshare05.c | 47 +++++++++++++++++++
 3 files changed, 49 insertions(+)
 create mode 100644 testcases/kernel/syscalls/unshare/unshare05.c

diff --git a/runtest/syscalls b/runtest/syscalls
index 57338297a..82e222bf4 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -1726,6 +1726,7 @@ unshare01 unshare01
 unshare02 unshare02
 unshare03 unshare03
 unshare04 unshare04
+unshare05 unshare05
 
 #
 # These tests require an unmounted block device
diff --git a/testcases/kernel/syscalls/unshare/.gitignore b/testcases/kernel/syscalls/unshare/.gitignore
index b1206e452..8ece5f988 100644
--- a/testcases/kernel/syscalls/unshare/.gitignore
+++ b/testcases/kernel/syscalls/unshare/.gitignore
@@ -2,3 +2,4 @@
 /unshare02
 /unshare03
 /unshare04
+/unshare05
diff --git a/testcases/kernel/syscalls/unshare/unshare05.c b/testcases/kernel/syscalls/unshare/unshare05.c
new file mode 100644
index 000000000..c85db36b9
--- /dev/null
+++ b/testcases/kernel/syscalls/unshare/unshare05.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025 lufei <lufei@uniontech.com>
+ */
+
+/*\
+ * This test case verifies unshare(CLONE_NEWPID) creates a new PID namespace
+ * and that the first child process in the new namespace gets PID 1.
+ */
+
+#define _GNU_SOURCE
+
+#include "tst_test.h"
+#include "lapi/sched.h"
+
+static struct tst_clone_args *args;
+
+static void setup(void)
+{
+	args->flags = CLONE_NEWPID;
+	args->exit_signal = SIGCHLD;
+}
+
+static void run(void)
+{
+	if (!SAFE_CLONE(args)) {
+		SAFE_UNSHARE(CLONE_NEWPID);
+
+		if (!SAFE_FORK()) {
+			TST_EXP_EQ_LI(getpid(), 1);
+			exit(0);
+		}
+
+		exit(0);
+	}
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.forks_child = 1,
+	.needs_root = 1,
+	.test_all = run,
+	.bufs = (struct tst_buffers []) {
+		{&args, .size = sizeof(*args)},
+		{},
+	}
+};
-- 
2.39.3