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Message-ID: <202003131607.10FDF99191@keescook>
Date: Fri, 13 Mar 2020 16:07:53 -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 2/3] binderfs_test: switch from /dev to a unique
per-test mountpoint
On Fri, Mar 13, 2020 at 04:24:19PM +0100, Christian Brauner wrote:
> Unprivileged users will be able to create directories in there. The
> unprivileged test for /dev wouldn't have worked on most systems.
>
> 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().
> ---
> .../filesystems/binderfs/binderfs_test.c | 47 +++++++++----------
> 1 file changed, 23 insertions(+), 24 deletions(-)
>
> diff --git a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
> index 0cfca65e095a..818eb49f8125 100644
> --- a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
> +++ b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
> @@ -139,29 +139,25 @@ static int __do_binderfs_test(void)
> int fd, ret, saved_errno;
> size_t len;
> ssize_t wret;
> - bool keep = false;
> struct binderfs_device device = { 0 };
> struct binder_version version = { 0 };
> + char binderfs_mntpt[] = P_tmpdir "/binderfs_XXXXXX",
> + device_path[sizeof(P_tmpdir "/binderfs_XXXXXX/") + BINDERFS_MAX_NAME];
>
> change_to_mountns();
>
> - ret = mkdir("/dev/binderfs", 0755);
> - if (ret < 0) {
> - if (errno != EEXIST)
> - ksft_exit_fail_msg(
> - "%s - Failed to create binderfs mountpoint\n",
> - strerror(errno));
> -
> - keep = true;
> - }
> + if (!mkdtemp(binderfs_mntpt))
> + ksft_exit_fail_msg(
> + "%s - Failed to create binderfs mountpoint\n",
> + strerror(errno));
>
> - ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
> + ret = mount(NULL, binderfs_mntpt, "binder", 0, 0);
> if (ret < 0) {
> if (errno != ENODEV)
> ksft_exit_fail_msg("%s - Failed to mount binderfs\n",
> strerror(errno));
>
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> return 1;
> }
>
> @@ -170,7 +166,8 @@ static int __do_binderfs_test(void)
>
> memcpy(device.name, "my-binder", strlen("my-binder"));
>
> - fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
> + snprintf(device_path, sizeof(device_path), "%s/binder-control", binderfs_mntpt);
> + fd = open(device_path, O_RDONLY | O_CLOEXEC);
> if (fd < 0)
> ksft_exit_fail_msg(
> "%s - Failed to open binder-control device\n",
> @@ -181,7 +178,7 @@ static int __do_binderfs_test(void)
> close(fd);
> errno = saved_errno;
> if (ret < 0) {
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> ksft_exit_fail_msg(
> "%s - Failed to allocate new binder device\n",
> strerror(errno));
> @@ -194,9 +191,10 @@ static int __do_binderfs_test(void)
> /* binder device allocation test passed */
> ksft_inc_pass_cnt();
>
> - fd = open("/dev/binderfs/my-binder", O_CLOEXEC | O_RDONLY);
> + snprintf(device_path, sizeof(device_path), "%s/my-binder", binderfs_mntpt);
> + fd = open(device_path, O_CLOEXEC | O_RDONLY);
> if (fd < 0) {
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> ksft_exit_fail_msg("%s - Failed to open my-binder device\n",
> strerror(errno));
> }
> @@ -206,7 +204,7 @@ static int __do_binderfs_test(void)
> close(fd);
> errno = saved_errno;
> if (ret < 0) {
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> ksft_exit_fail_msg(
> "%s - Failed to open perform BINDER_VERSION request\n",
> strerror(errno));
> @@ -218,9 +216,9 @@ static int __do_binderfs_test(void)
> /* binder transaction with binderfs binder device passed */
> ksft_inc_pass_cnt();
>
> - ret = unlink("/dev/binderfs/my-binder");
> + ret = unlink(device_path);
> if (ret < 0) {
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> ksft_exit_fail_msg("%s - Failed to delete binder device\n",
> strerror(errno));
> }
> @@ -228,12 +226,13 @@ static int __do_binderfs_test(void)
> /* binder device removal passed */
> ksft_inc_pass_cnt();
>
> - ret = unlink("/dev/binderfs/binder-control");
> + snprintf(device_path, sizeof(device_path), "%s/binder-control", binderfs_mntpt);
> + ret = unlink(device_path);
> if (!ret) {
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> ksft_exit_fail_msg("Managed to delete binder-control device\n");
> } else if (errno != EPERM) {
> - keep ? : rmdir_protect_errno("/dev/binderfs");
> + rmdir_protect_errno(binderfs_mntpt);
> ksft_exit_fail_msg(
> "%s - Failed to delete binder-control device but exited with unexpected error code\n",
> strerror(errno));
> @@ -243,8 +242,8 @@ static int __do_binderfs_test(void)
> ksft_inc_xfail_cnt();
>
> on_error:
> - ret = umount2("/dev/binderfs", MNT_DETACH);
> - keep ?: rmdir_protect_errno("/dev/binderfs");
> + ret = umount2(binderfs_mntpt, MNT_DETACH);
> + rmdir_protect_errno(binderfs_mntpt);
> if (ret < 0)
> ksft_exit_fail_msg("%s - Failed to unmount binderfs\n",
> strerror(errno));
> --
> 2.25.1
>
--
Kees Cook
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