selftests/filesystems: add utils.{c,h}

Add a new set of helpers that will be used in follow-up patches.

Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/tools/testing/selftests/filesystems/utils.h b/tools/testing/selftests/filesystems/utils.h
new file mode 100644
index 000000000000..f35001a75f99
--- /dev/null
+++ b/tools/testing/selftests/filesystems/utils.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __IDMAP_UTILS_H
+#define __IDMAP_UTILS_H
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <errno.h>
+#include <linux/types.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/capability.h>
+#include <sys/fsuid.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+extern int get_userns_fd(unsigned long nsid, unsigned long hostid,
+			 unsigned long range);
+
+extern int caps_down(void);
+
+extern bool switch_ids(uid_t uid, gid_t gid);
+
+static inline bool switch_userns(int fd, uid_t uid, gid_t gid, bool drop_caps)
+{
+	if (setns(fd, CLONE_NEWUSER))
+		return false;
+
+	if (!switch_ids(uid, gid))
+		return false;
+
+	if (drop_caps && !caps_down())
+		return false;
+
+	return true;
+}
+
+#endif /* __IDMAP_UTILS_H */