selftests: add binderfs selftests

This adds the promised selftest for binderfs. It will verify the following
things:
- binderfs mounting works
- binder device allocation works
- performing a binder ioctl() request through a binderfs device works
- binder device removal works
- binder-control removal fails
- binderfs unmounting works

The tests are performed both privileged and unprivileged. The latter
verifies that binderfs behaves correctly in user namespaces.

Cc: Todd Kjos <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>
Acked-by: Shuah Khan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

tools/testing/selftests/Makefile

···
 TARGETS += efivarfs
 TARGETS += exec
 TARGETS += filesystems
+TARGETS += filesystems/binderfs
 TARGETS += firmware
 TARGETS += ftrace
 TARGETS += futex

tools/testing/selftests/filesystems/binderfs/.gitignore

···
+binderfs_test

tools/testing/selftests/filesystems/binderfs/Makefile

···
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += -I../../../../../usr/include/
+TEST_GEN_PROGS := binderfs_test
+
+include ../../lib.mk

tools/testing/selftests/filesystems/binderfs/binderfs_test.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <linux/android/binder.h>
+#include <linux/android/binderfs.h>
+#include "../../kselftest.h"
+
+static ssize_t write_nointr(int fd, const void *buf, size_t count)
+{
+	ssize_t ret;
+again:
+	ret = write(fd, buf, count);
+	if (ret < 0 && errno == EINTR)
+		goto again;
+
+	return ret;
+}
+
+static void write_to_file(const char *filename, const void *buf, size_t count,
+			  int allowed_errno)
+{
+	int fd, saved_errno;
+	ssize_t ret;
+
+	fd = open(filename, O_WRONLY | O_CLOEXEC);
+	if (fd < 0)
+		ksft_exit_fail_msg("%s - Failed to open file %s\n",
+				   strerror(errno), filename);
+
+	ret = write_nointr(fd, buf, count);
+	if (ret < 0) {
+		if (allowed_errno && (errno == allowed_errno)) {
+			close(fd);
+			return;
+		}
+
+		goto on_error;
+	}
+
+	if ((size_t)ret != count)
+		goto on_error;
+
+	close(fd);
+	return;
+
+on_error:
+	saved_errno = errno;
+	close(fd);
+	errno = saved_errno;
+
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to write to file %s\n",
+				   strerror(errno), filename);
+
+	ksft_exit_fail_msg("Failed to write to file %s\n", filename);
+}
+
+static void change_to_userns(void)
+{
+	int ret;
+	uid_t uid;
+	gid_t gid;
+	/* {g,u}id_map files only allow a max of 4096 bytes written to them */
+	char idmap[4096];
+
+	uid = getuid();
+	gid = getgid();
+
+	ret = unshare(CLONE_NEWUSER);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to unshare user namespace\n",
+				   strerror(errno));
+
+	write_to_file("/proc/self/setgroups", "deny", strlen("deny"), ENOENT);
+
+	ret = snprintf(idmap, sizeof(idmap), "0 %d 1", uid);
+	if (ret < 0 || (size_t)ret >= sizeof(idmap))
+		ksft_exit_fail_msg("%s - Failed to prepare uid mapping\n",
+				   strerror(errno));
+
+	write_to_file("/proc/self/uid_map", idmap, strlen(idmap), 0);
+
+	ret = snprintf(idmap, sizeof(idmap), "0 %d 1", gid);
+	if (ret < 0 || (size_t)ret >= sizeof(idmap))
+		ksft_exit_fail_msg("%s - Failed to prepare uid mapping\n",
+				   strerror(errno));
+
+	write_to_file("/proc/self/gid_map", idmap, strlen(idmap), 0);
+
+	ret = setgid(0);
+	if (ret)
+		ksft_exit_fail_msg("%s - Failed to setgid(0)\n",
+				   strerror(errno));
+
+	ret = setuid(0);
+	if (ret)
+		ksft_exit_fail_msg("%s - Failed to setgid(0)\n",
+				   strerror(errno));
+}
+
+static void change_to_mountns(void)
+{
+	int ret;
+
+	ret = unshare(CLONE_NEWNS);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to unshare mount namespace\n",
+				   strerror(errno));
+
+	ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to mount / as private\n",
+				   strerror(errno));
+}
+
+static void rmdir_protect_errno(const char *dir)
+{
+	int saved_errno = errno;
+	(void)rmdir(dir);
+	errno = saved_errno;
+}
+
+static void __do_binderfs_test(void)
+{
+	int fd, ret, saved_errno;
+	size_t len;
+	ssize_t wret;
+	bool keep = false;
+	struct binderfs_device device = { 0 };
+	struct binder_version version = { 0 };
+
+	change_to_mountns();
+
+	ret = mkdir("/dev/binderfs", 0755);
+	if (ret < 0) {
+		if (errno != EEXIST)
+			ksft_exit_fail_msg(
+				"%s - Failed to create binderfs mountpoint\n",
+				strerror(errno));
+
+		keep = true;
+	}
+
+	ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
+	if (ret < 0) {
+		if (errno != ENODEV)
+			ksft_exit_fail_msg("%s - Failed to mount binderfs\n",
+					   strerror(errno));
+
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_skip(
+			"The Android binderfs filesystem is not available\n");
+	}
+
+	/* binderfs mount test passed */
+	ksft_inc_pass_cnt();
+
+	memcpy(device.name, "my-binder", strlen("my-binder"));
+
+	fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
+	if (fd < 0)
+		ksft_exit_fail_msg(
+			"%s - Failed to open binder-control device\n",
+			strerror(errno));
+
+	ret = ioctl(fd, BINDER_CTL_ADD, &device);
+	saved_errno = errno;
+	close(fd);
+	errno = saved_errno;
+	if (ret < 0) {
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_fail_msg(
+			"%s - Failed to allocate new binder device\n",
+			strerror(errno));
+	}
+
+	ksft_print_msg(
+		"Allocated new binder device with major %d, minor %d, and name %s\n",
+		device.major, device.minor, device.name);
+
+	/* binder device allocation test passed */
+	ksft_inc_pass_cnt();
+
+	fd = open("/dev/binderfs/my-binder", O_CLOEXEC | O_RDONLY);
+	if (fd < 0) {
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_fail_msg("%s - Failed to open my-binder device\n",
+				   strerror(errno));
+	}
+
+	ret = ioctl(fd, BINDER_VERSION, &version);
+	saved_errno = errno;
+	close(fd);
+	errno = saved_errno;
+	if (ret < 0) {
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_fail_msg(
+			"%s - Failed to open perform BINDER_VERSION request\n",
+			strerror(errno));
+	}
+
+	ksft_print_msg("Detected binder version: %d\n",
+		       version.protocol_version);
+
+	/* binder transaction with binderfs binder device passed */
+	ksft_inc_pass_cnt();
+
+	ret = unlink("/dev/binderfs/my-binder");
+	if (ret < 0) {
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_fail_msg("%s - Failed to delete binder device\n",
+				   strerror(errno));
+	}
+
+	/* binder device removal passed */
+	ksft_inc_pass_cnt();
+
+	ret = unlink("/dev/binderfs/binder-control");
+	if (!ret) {
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_fail_msg("Managed to delete binder-control device\n");
+	} else if (errno != EPERM) {
+		keep ? : rmdir_protect_errno("/dev/binderfs");
+		ksft_exit_fail_msg(
+			"%s - Failed to delete binder-control device but exited with unexpected error code\n",
+			strerror(errno));
+	}
+
+	/* binder-control device removal failed as expected */
+	ksft_inc_xfail_cnt();
+
+on_error:
+	ret = umount2("/dev/binderfs", MNT_DETACH);
+	keep ?: rmdir_protect_errno("/dev/binderfs");
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to unmount binderfs\n",
+				   strerror(errno));
+
+	/* binderfs unmount test passed */
+	ksft_inc_pass_cnt();
+}
+
+static void binderfs_test_privileged()
+{
+	if (geteuid() != 0)
+		ksft_print_msg(
+			"Tests are not run as root. Skipping privileged tests\n");
+	else
+		__do_binderfs_test();
+}
+
+static void binderfs_test_unprivileged()
+{
+	change_to_userns();
+	__do_binderfs_test();
+}
+
+int main(int argc, char *argv[])
+{
+	binderfs_test_privileged();
+	binderfs_test_unprivileged();
+	ksft_exit_pass();
+}

tools/testing/selftests/filesystems/binderfs/config

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+CONFIG_ANDROID=y
+CONFIG_ANDROID_BINDERFS=y
+CONFIG_ANDROID_BINDER_IPC=y