Message-ID: <202003131608.DA96ECE4D@keescook>
Date:   Fri, 13 Mar 2020 16:08:07 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     gregkh@...uxfoundation.org, tkjos@...roid.com,
        linux-kernel@...r.kernel.org, ard.biesheuvel@...aro.org,
        ardb@...nel.org, arve@...roid.com, hridya@...gle.com,
        joel@...lfernandes.org, john.stultz@...aro.org,
        kernel-team@...roid.com, linux-kselftest@...r.kernel.org,
        maco@...roid.com, naresh.kamboju@...aro.org, shuah@...nel.org
Subject: Re: [PATCH v2 3/3] binderfs: add stress test for binderfs binder
 devices

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@...omium.org>:
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
> /* v2 */
> - Kees Cook <keescook@...omium.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
> 

-- 
Kees Cook

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