selftests/open_tree: add OPEN_TREE_NAMESPACE tests

Add tests for OPEN_TREE_NAMESPACE.

Link: https://patch.msgid.link/[email protected]
Tested-by: Jeff Layton <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

tools/testing/selftests/filesystems/open_tree_ns/.gitignore

@@ -0,0 +1 @@
+open_tree_ns_test

tools/testing/selftests/filesystems/open_tree_ns/Makefile

@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+TEST_GEN_PROGS := open_tree_ns_test
+
+CFLAGS := -Wall -Werror -g $(KHDR_INCLUDES)
+LDLIBS := -lcap
+
+include ../../lib.mk
+
+$(OUTPUT)/open_tree_ns_test: open_tree_ns_test.c ../utils.c
+	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)

tools/testing/selftests/filesystems/utils.c

@@ -515,6 +515,32 @@ int setup_userns(void)
 	return 0;
 }
 
+int enter_userns(void)
+{
+	int ret;
+	char buf[32];
+	uid_t uid = getuid();
+	gid_t gid = getgid();
+
+	ret = unshare(CLONE_NEWUSER);
+	if (ret)
+		return ret;
+
+	sprintf(buf, "0 %d 1", uid);
+	ret = write_file("/proc/self/uid_map", buf);
+	if (ret)
+		return ret;
+	ret = write_file("/proc/self/setgroups", "deny");
+	if (ret)
+		return ret;
+	sprintf(buf, "0 %d 1", gid);
+	ret = write_file("/proc/self/gid_map", buf);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
 /* caps_down - lower all effective caps */
 int caps_down(void)
 {

tools/testing/selftests/filesystems/utils.h

@@ -28,6 +28,7 @@ extern int cap_down(cap_value_t down);
 
 extern bool switch_ids(uid_t uid, gid_t gid);
 extern int setup_userns(void);
+extern int enter_userns(void);
 
 static inline bool switch_userns(int fd, uid_t uid, gid_t gid, bool drop_caps)
 {