Re: [PATCH v2 2/3] binderfs_test: switch from /dev to a unique per-test mountpoint

[Kees Cook <keescook@chromium.org>]

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@chromium.org>:
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

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

-Kees

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