tools/nolibc: add namespace functionality

This is used in various selftests and will be handy when integrating
those with nolibc.

Not all configurations support namespaces, so skip the tests where
necessary.  Also if the tests are running without privileges.
Enable the namespace configuration for those architectures where it is not
enabled by default.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250428-nolibc-misc-v2-12-3c043eeab06c@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

2 files changed, 69 insertions, 0 deletions

diff --git a/tools/testing/selftests/nolibc/Makefile b/tools/testing/selftests/nolibc/Makefile
index 2671383045db..94176ffe4646 100644
--- a/tools/testing/selftests/nolibc/Makefile
+++ b/tools/testing/selftests/nolibc/Makefile
@@ -109,6 +109,8 @@ DEFCONFIG            = $(DEFCONFIG_$(XARCH))
 
 EXTRACONFIG_m68k      = -e CONFIG_BLK_DEV_INITRD
 EXTRACONFIG           = $(EXTRACONFIG_$(XARCH))
+EXTRACONFIG_arm       = -e CONFIG_NAMESPACES
+EXTRACONFIG_armthumb  = -e CONFIG_NAMESPACES
 
 # optional tests to run (default = all)
 TEST =
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 665d7631fbc6..d1157319b5d7 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1172,6 +1172,72 @@ int test_openat(void)
 	return 0;
 }
 
+int test_namespace(void)
+{
+	int original_ns, new_ns, ret;
+	ino_t original_ns_ino;
+	struct stat stat_buf;
+
+	original_ns = open("/proc/self/ns/uts", O_RDONLY);
+	if (original_ns == -1)
+		return -1;
+
+	ret = fstat(original_ns, &stat_buf);
+	if (ret)
+		goto out;
+
+	original_ns_ino = stat_buf.st_ino;
+
+	ret = unshare(CLONE_NEWUTS);
+	if (ret)
+		goto out;
+
+	new_ns = open("/proc/self/ns/uts", O_RDONLY);
+	if (new_ns == -1) {
+		ret = new_ns;
+		goto out;
+	}
+
+	ret = fstat(new_ns, &stat_buf);
+	close(new_ns);
+	if (ret)
+		goto out;
+
+	if (stat_buf.st_ino == original_ns_ino) {
+		errno = EINVAL;
+		ret = -1;
+		goto out;
+	}
+
+	ret = setns(original_ns, CLONE_NEWUTS);
+	if (ret)
+		goto out;
+
+	new_ns = open("/proc/self/ns/uts", O_RDONLY);
+	if (new_ns == -1) {
+		ret = new_ns;
+		goto out;
+	}
+
+	ret = fstat(new_ns, &stat_buf);
+	if (ret)
+		goto out;
+
+	close(new_ns);
+
+	if (stat_buf.st_ino != original_ns_ino) {
+		errno = EINVAL;
+		ret = -1;
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	close(original_ns);
+	return ret;
+}
+
 /* Run syscall tests between IDs <min> and <max>.
  * Return 0 on success, non-zero on failure.
  */
@@ -1296,6 +1362,7 @@ int run_syscall(int min, int max)
 		CASE_TEST(write_zero);        EXPECT_SYSZR(1, write(1, &tmp, 0)); break;
 		CASE_TEST(syscall_noargs);    EXPECT_SYSEQ(1, syscall(__NR_getpid), getpid()); break;
 		CASE_TEST(syscall_args);      EXPECT_SYSER(1, syscall(__NR_statx, 0, NULL, 0, 0, NULL), -1, EFAULT); break;
+		CASE_TEST(namespace);         EXPECT_SYSZR(euid0 && proc, test_namespace()); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */