binderfs: add stress test for binderfs binder devices

This adds a stress test that should hopefully help us catch regressions
for [1], [2], and [3].

[1]: 2669b8b0c798 ("binder: prevent UAF for binderfs devices")
[2]: f0fe2c0f050d ("binder: prevent UAF for binderfs devices II")
[3]: 211b64e4b5b6 ("binderfs: use refcount for binder control devices too")
Signed-off-by: Christian Brauner <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

tools/testing/selftests/filesystems/binderfs/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 
-CFLAGS += -I../../../../../usr/include/
+CFLAGS += -I../../../../../usr/include/ -pthread
 TEST_GEN_PROGS := binderfs_test
 
 binderfs_test: binderfs_test.c ../../kselftest.h ../../kselftest_harness.h

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

···
 #define _GNU_SOURCE
 #include <errno.h>
 #include <fcntl.h>
+#include <pthread.h>
 #include <sched.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/fsuid.h>
 #include <sys/ioctl.h>
 #include <sys/mount.h>
+#include <sys/socket.h>
 #include <sys/stat.h>
+#include <sys/sysinfo.h>
 #include <sys/types.h>
+#include <sys/wait.h>
 #include <unistd.h>
 #include <linux/android/binder.h>
 #include <linux/android/binderfs.h>
···
 #include "../../kselftest.h"
 #include "../../kselftest_harness.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;
+#define DEFAULT_THREADS 4
 
-	return ret;
-}
+#define PTR_TO_INT(p) ((int)((intptr_t)(p)))
+#define INT_TO_PTR(u) ((void *)((intptr_t)(u)))
 
-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;
+#define close_prot_errno_disarm(fd) \
+	if (fd >= 0) {              \
+		int _e_ = errno;    \
+		close(fd);          \
+		errno = _e_;        \
+		fd = -EBADF;        \
 	}
 
-	if ((size_t)ret != count)
-		goto on_error;
+#define log_exit(format, ...)                                                  \
+	({                                                                     \
+		fprintf(stderr, format "\n", ##__VA_ARGS__);                   \
+		exit(EXIT_FAILURE);                                            \
+	})
 
-	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)
+static void change_mountns(void)
 {
 	int ret;
 
···
 	char binderfs_mntpt[] = P_tmpdir "/binderfs_XXXXXX",
 		device_path[sizeof(P_tmpdir "/binderfs_XXXXXX/") + BINDERFS_MAX_NAME];
 
-	change_to_mountns();
+	change_mountns();
 
 	if (!mkdtemp(binderfs_mntpt))
 		ksft_exit_fail_msg(
···
 	return 0;
 }
 
+static int wait_for_pid(pid_t pid)
+{
+	int status, ret;
+
+again:
+	ret = waitpid(pid, &status, 0);
+	if (ret == -1) {
+		if (errno == EINTR)
+			goto again;
+
+		return -1;
+	}
+
+	if (!WIFEXITED(status))
+		return -1;
+
+	return WEXITSTATUS(status);
+}
+
+static int setid_userns_root(void)
+{
+	if (setuid(0))
+		return -1;
+	if (setgid(0))
+		return -1;
+
+	setfsuid(0);
+	setfsgid(0);
+
+	return 0;
+}
+
+enum idmap_type {
+	UID_MAP,
+	GID_MAP,
+};
+
+static ssize_t read_nointr(int fd, void *buf, size_t count)
+{
+	ssize_t ret;
+again:
+	ret = read(fd, buf, count);
+	if (ret < 0 && errno == EINTR)
+		goto again;
+
+	return ret;
+}
+
+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 int write_id_mapping(enum idmap_type type, pid_t pid, const char *buf,
+			    size_t buf_size)
+{
+	int fd;
+	int ret;
+	char path[4096];
+
+	if (type == GID_MAP) {
+		int setgroups_fd;
+
+		snprintf(path, sizeof(path), "/proc/%d/setgroups", pid);
+		setgroups_fd = open(path, O_WRONLY | O_CLOEXEC | O_NOFOLLOW);
+		if (setgroups_fd < 0 && errno != ENOENT)
+			return -1;
+
+		if (setgroups_fd >= 0) {
+			ret = write_nointr(setgroups_fd, "deny", sizeof("deny") - 1);
+			close_prot_errno_disarm(setgroups_fd);
+			if (ret != sizeof("deny") - 1)
+				return -1;
+		}
+	}
+
+	switch (type) {
+	case UID_MAP:
+		ret = snprintf(path, sizeof(path), "/proc/%d/uid_map", pid);
+		break;
+	case GID_MAP:
+		ret = snprintf(path, sizeof(path), "/proc/%d/gid_map", pid);
+		break;
+	default:
+		return -1;
+	}
+	if (ret < 0 || ret >= sizeof(path))
+		return -E2BIG;
+
+	fd = open(path, O_WRONLY | O_CLOEXEC | O_NOFOLLOW);
+	if (fd < 0)
+		return -1;
+
+	ret = write_nointr(fd, buf, buf_size);
+	close_prot_errno_disarm(fd);
+	if (ret != buf_size)
+		return -1;
+
+	return 0;
+}
+
+static void change_userns(int syncfds[2])
+{
+	int ret;
+	char buf;
+
+	close_prot_errno_disarm(syncfds[1]);
+
+	ret = unshare(CLONE_NEWUSER);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to unshare user namespace\n",
+				   strerror(errno));
+
+	ret = write_nointr(syncfds[0], "1", 1);
+	if (ret != 1)
+		ksft_exit_fail_msg("write_nointr() failed\n");
+
+	ret = read_nointr(syncfds[0], &buf, 1);
+	if (ret != 1)
+		ksft_exit_fail_msg("read_nointr() failed\n");
+
+	close_prot_errno_disarm(syncfds[0]);
+
+	if (setid_userns_root())
+		ksft_exit_fail_msg("setid_userns_root() failed");
+}
+
+static void change_idmaps(int syncfds[2], pid_t pid)
+{
+	int ret;
+	char buf;
+	char id_map[4096];
+
+	close_prot_errno_disarm(syncfds[0]);
+
+	ret = read_nointr(syncfds[1], &buf, 1);
+	if (ret != 1)
+		ksft_exit_fail_msg("read_nointr() failed\n");
+
+	snprintf(id_map, sizeof(id_map), "0 %d 1\n", getuid());
+	ret = write_id_mapping(UID_MAP, pid, id_map, strlen(id_map));
+	if (ret)
+		ksft_exit_fail_msg("write_id_mapping(UID_MAP) failed");
+
+	snprintf(id_map, sizeof(id_map), "0 %d 1\n", getgid());
+	ret = write_id_mapping(GID_MAP, pid, id_map, strlen(id_map));
+	if (ret)
+		ksft_exit_fail_msg("write_id_mapping(GID_MAP) failed");
+
+	ret = write_nointr(syncfds[1], "1", 1);
+	if (ret != 1)
+		ksft_exit_fail_msg("write_nointr() failed");
+
+	close_prot_errno_disarm(syncfds[1]);
+}
+
+static void *binder_version_thread(void *data)
+{
+	int fd = PTR_TO_INT(data);
+	struct binder_version version = { 0 };
+	int ret;
+
+	ret = ioctl(fd, BINDER_VERSION, &version);
+	if (ret < 0)
+		ksft_print_msg("%s - Failed to open perform BINDER_VERSION request\n", strerror(errno));
+
+	pthread_exit(data);
+}
+
+/*
+ * Regression test:
+ * 2669b8b0c798 ("binder: prevent UAF for binderfs devices")
+ * f0fe2c0f050d ("binder: prevent UAF for binderfs devices II")
+ * 211b64e4b5b6 ("binderfs: use refcount for binder control devices too")
+ */
+TEST(binderfs_stress)
+{
+	int fds[1000];
+	int syncfds[2];
+	pid_t pid;
+	int fd, ret;
+	size_t len;
+	struct binderfs_device device = { 0 };
+	char binderfs_mntpt[] = P_tmpdir "/binderfs_XXXXXX",
+		device_path[sizeof(P_tmpdir "/binderfs_XXXXXX/") + BINDERFS_MAX_NAME];
+
+	ret = socketpair(PF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0, syncfds);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to create socket pair", strerror(errno));
+
+	pid = fork();
+	if (pid < 0) {
+		close_prot_errno_disarm(syncfds[0]);
+		close_prot_errno_disarm(syncfds[1]);
+		ksft_exit_fail_msg("%s - Failed to fork", strerror(errno));
+	}
+
+	if (pid == 0) {
+		int i, j, k, nthreads;
+		pthread_attr_t attr;
+		pthread_t threads[DEFAULT_THREADS];
+		change_userns(syncfds);
+		change_mountns();
+
+		if (!mkdtemp(binderfs_mntpt))
+			log_exit("%s - Failed to create binderfs mountpoint\n",
+				 strerror(errno));
+
+		ret = mount(NULL, binderfs_mntpt, "binder", 0, 0);
+		if (ret < 0)
+			log_exit("%s - Failed to mount binderfs\n", strerror(errno));
+
+		for (int i = 0; i < ARRAY_SIZE(fds); i++) {
+
+			snprintf(device_path, sizeof(device_path),
+				 "%s/binder-control", binderfs_mntpt);
+			fd = open(device_path, O_RDONLY | O_CLOEXEC);
+			if (fd < 0)
+				log_exit("%s - Failed to open binder-control device\n", strerror(errno));
+
+			memset(&device, 0, sizeof(device));
+			snprintf(device.name, sizeof(device.name), "%d", i);
+			ret = ioctl(fd, BINDER_CTL_ADD, &device);
+			close_prot_errno_disarm(fd);
+			if (ret < 0)
+				log_exit("%s - Failed to allocate new binder device\n", strerror(errno));
+
+			snprintf(device_path, sizeof(device_path), "%s/%d",
+				 binderfs_mntpt, i);
+			fds[i] = open(device_path, O_RDONLY | O_CLOEXEC);
+			if (fds[i] < 0)
+				log_exit("%s - Failed to open binder device\n", strerror(errno));
+		}
+
+		ret = umount2(binderfs_mntpt, MNT_DETACH);
+		rmdir_protect_errno(binderfs_mntpt);
+		if (ret < 0)
+			log_exit("%s - Failed to unmount binderfs\n", strerror(errno));
+
+		nthreads = get_nprocs_conf();
+		if (nthreads > DEFAULT_THREADS)
+			nthreads = DEFAULT_THREADS;
+
+		pthread_attr_init(&attr);
+		for (k = 0; k < ARRAY_SIZE(fds); k++) {
+			for (i = 0; i < nthreads; i++) {
+				ret = pthread_create(&threads[i], &attr, binder_version_thread, INT_TO_PTR(fds[k]));
+				if (ret) {
+					ksft_print_msg("%s - Failed to create thread %d\n", strerror(errno), i);
+					break;
+				}
+			}
+
+			for (j = 0; j < i; j++) {
+				void *fdptr = NULL;
+
+				ret = pthread_join(threads[j], &fdptr);
+				if (ret)
+					ksft_print_msg("%s - Failed to join thread %d for fd %d\n", strerror(errno), j, PTR_TO_INT(fdptr));
+			}
+		}
+		pthread_attr_destroy(&attr);
+
+		for (k = 0; k < ARRAY_SIZE(fds); k++)
+			close(fds[k]);
+
+		exit(EXIT_SUCCESS);
+	}
+
+	change_idmaps(syncfds, pid);
+
+	ret = wait_for_pid(pid);
+	if (ret)
+		ksft_exit_fail_msg("wait_for_pid() failed");
+}
+
 TEST(binderfs_test_privileged)
 {
 	if (geteuid() != 0)
···
 
 TEST(binderfs_test_unprivileged)
 {
-	change_to_userns();
+	int ret;
+	int syncfds[2];
+	pid_t pid;
 
-	if (__do_binderfs_test() == 1)
-		XFAIL(return, "The Android binderfs filesystem is not available");
+	ret = socketpair(PF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0, syncfds);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - Failed to create socket pair", strerror(errno));
+
+	pid = fork();
+	if (pid < 0) {
+		close_prot_errno_disarm(syncfds[0]);
+		close_prot_errno_disarm(syncfds[1]);
+		ksft_exit_fail_msg("%s - Failed to fork", strerror(errno));
+	}
+
+	if (pid == 0) {
+		change_userns(syncfds);
+		if (__do_binderfs_test() == 1)
+			exit(2);
+		exit(EXIT_SUCCESS);
+	}
+
+	change_idmaps(syncfds, pid);
+
+	ret = wait_for_pid(pid);
+	if (ret) {
+		if (ret == 2)
+			XFAIL(return, "The Android binderfs filesystem is not available");
+		else
+			ksft_exit_fail_msg("wait_for_pid() failed");
+	}
 }
 
 TEST_HARNESS_MAIN