selftests/fsmount_ns: add missing TARGETS and fix cap test

Add missing top-level kselftest TARGETS entries for empty_mntns and
fsmount_ns so that 'make kselftest' discovers and runs these tests.

Fix requires_cap_sys_admin test which always SKIPped because fsopen()
was called after enter_userns(), where CAP_SYS_ADMIN in the mount
namespace's user_ns is unavailable. Move fsopen/fsconfig before fork so
the configured fs_fd is inherited by the child, which then only needs to
call fsmount() after dropping privileges.

Fixes: 3ac7ea91f3d0 ("selftests: add FSMOUNT_NAMESPACE tests")
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 15 insertions, 16 deletions

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 2d05b3e1a26e..5677dd8b2a76 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -39,6 +39,8 @@ TARGETS += filesystems/statmount
 TARGETS += filesystems/mount-notify
 TARGETS += filesystems/fuse
 TARGETS += filesystems/move_mount
+TARGETS += filesystems/empty_mntns
+TARGETS += filesystems/fsmount_ns
 TARGETS += firmware
 TARGETS += fpu
 TARGETS += ftrace
diff --git a/tools/testing/selftests/filesystems/fsmount_ns/fsmount_ns_test.c b/tools/testing/selftests/filesystems/fsmount_ns/fsmount_ns_test.c
index 239abbe63814..b70b3051eed4 100644
--- a/tools/testing/selftests/filesystems/fsmount_ns/fsmount_ns_test.c
+++ b/tools/testing/selftests/filesystems/fsmount_ns/fsmount_ns_test.c
@@ -388,12 +388,23 @@ TEST_F(fsmount_ns_caps, requires_cap_sys_admin)
 {
 	pid_t pid;
 	int status;
+	int fs_fd;
+
+	/*
+	 * Prepare the configured filesystem fd as root before forking.
+	 * fsopen() requires CAP_SYS_ADMIN in the mount namespace's
+	 * user_ns, which won't be available after enter_userns().
+	 */
+	fs_fd = sys_fsopen("tmpfs", FSOPEN_CLOEXEC);
+	ASSERT_GE(fs_fd, 0);
+
+	ASSERT_EQ(sys_fsconfig(fs_fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0), 0);
 
 	pid = fork();
 	ASSERT_GE(pid, 0);
 
 	if (pid == 0) {
-		int fs_fd, fd;
+		int fd;
 
 		/* Child: drop privileges using utils.h helper */
 		if (enter_userns() != 0)
@@ -403,15 +414,6 @@ TEST_F(fsmount_ns_caps, requires_cap_sys_admin)
 		if (caps_down() == 0)
 			_exit(3);
 
-		fs_fd = sys_fsopen("tmpfs", FSOPEN_CLOEXEC);
-		if (fs_fd < 0)
-			_exit(4);
-
-		if (sys_fsconfig(fs_fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) < 0) {
-			close(fs_fd);
-			_exit(5);
-		}
-
 		fd = sys_fsmount(fs_fd, FSMOUNT_NAMESPACE | FSMOUNT_CLOEXEC, 0);
 		close(fs_fd);
 
@@ -432,6 +434,7 @@ TEST_F(fsmount_ns_caps, requires_cap_sys_admin)
 		_exit(7);
 	}
 
+	close(fs_fd);
 	ASSERT_EQ(waitpid(pid, &status, 0), pid);
 	ASSERT_TRUE(WIFEXITED(status));
 
@@ -448,12 +451,6 @@ TEST_F(fsmount_ns_caps, requires_cap_sys_admin)
 	case 3:
 		SKIP(return, "caps_down failed");
 		break;
-	case 4:
-		SKIP(return, "fsopen failed in userns");
-		break;
-	case 5:
-		SKIP(return, "fsconfig CMD_CREATE failed in userns");
-		break;
 	case 6:
 		SKIP(return, "FSMOUNT_NAMESPACE not supported");
 		break;