Re: [PATCH v2 3/3] binderfs: add stress test for binderfs binder devices

[Hridya Valsaraju]

On Fri, Mar 13, 2020 at 4:08 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> 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
>

Thank you for creating these tests Christian! I was able to get them
running on the cuttlefish platform with the ACK android-mainline
branch.

Regards,
Hridya

> > ---
> > /* 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