On Fri, Mar 13, 2020 at 04:24:20PM +0100, Christian Brauner wrote:
> 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@xxxxxxxxxxxx>:
> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
> ---
> /* v2 */
> - Kees Cook <keescook@xxxxxxxxxxxx>:
> - 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
>
--
Kees Cook
