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 <tkjos@google.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Shuah Khan <shuah@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

5 files changed, 286 insertions, 0 deletions

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 1a2bd15c5b6e..400ee81a3043 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -10,6 +10,7 @@ TARGETS += drivers/dma-buf
 TARGETS += efivarfs
 TARGETS += exec
 TARGETS += filesystems
+TARGETS += filesystems/binderfs
 TARGETS += firmware
 TARGETS += ftrace
 TARGETS += futex
diff --git a/tools/testing/selftests/filesystems/binderfs/.gitignore b/tools/testing/selftests/filesystems/binderfs/.gitignore
new file mode 100644
index 000000000000..8a5d9bf63dd4
--- /dev/null
+++ b/tools/testing/selftests/filesystems/binderfs/.gitignore
@@ -0,0 +1 @@
+binderfs_test
diff --git a/tools/testing/selftests/filesystems/binderfs/Makefile b/tools/testing/selftests/filesystems/binderfs/Makefile
new file mode 100644
index 000000000000..58cb659b56b4
--- /dev/null
+++ b/tools/testing/selftests/filesystems/binderfs/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += -I../../../../../usr/include/
+TEST_GEN_PROGS := binderfs_test
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
new file mode 100644
index 000000000000..8c2ed962e1c7
--- /dev/null
+++ b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
@@ -0,0 +1,275 @@
+// 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",