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Subject[PATCH v2 3/3] binderfs: add stress test for binderfs binder devices
Date
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")
Cc: Kees Cook <keescook@chromium.org>:
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
- Kees Cook <keescook@chromium.org>:
- Switch to unique mountpoint through mkdtemp().
---
.../selftests/filesystems/binderfs/Makefile | 2 +-
.../filesystems/binderfs/binderfs_test.c | 426 ++++++++++++++----
2 files changed, 334 insertions(+), 94 deletions(-)

diff --git a/tools/testing/selftests/filesystems/binderfs/Makefile b/tools/testing/selftests/filesystems/binderfs/Makefile
index 75315d9ba7a9..8af25ae96049 100644
--- a/tools/testing/selftests/filesystems/binderfs/Makefile
+++ b/tools/testing/selftests/filesystems/binderfs/Makefile
@@ -1,6 +1,6 @@
# 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
diff --git a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
index 818eb49f8125..8a6b507e34a8 100644
--- a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
+++ b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
@@ -3,15 +3,20 @@
#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>
@@ -19,100 +24,26 @@
#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;
-
- 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);
+#define DEFAULT_THREADS 4

- ret = write_nointr(fd, buf, count);
- if (ret < 0) {
- if (allowed_errno && (errno == allowed_errno)) {
- close(fd);
- return;
- }
+#define PTR_TO_INT(p) ((int)((intptr_t)(p)))
+#define INT_TO_PTR(u) ((void *)((intptr_t)(u)))

- 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;
-
- 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));
+#define log_exit(format, ...) \
+ ({ \
+ fprintf(stderr, format "\n", ##__VA_ARGS__); \
+ exit(EXIT_FAILURE); \
+ })

- 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;

@@ -144,7 +75,7 @@ static int __do_binderfs_test(void)
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(
@@ -253,6 +184,288 @@ static int __do_binderfs_test(void)
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)
@@ -264,10 +477,37 @@ TEST(binderfs_test_privileged)

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
--
2.25.1
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