Re: [PATCH 3/3] binderfs_test: switch from /dev to /tmp as mountpoint

From: Kees Cook <keescook@chromium.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Todd Kjos" <tkjos@android.com>,
	ard.biesheuvel@linaro.org, ardb@kernel.org,
	john.stultz@linaro.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, naresh.kamboju@linaro.org,
	shuah@kernel.org, "Arve Hjønnevåg" <arve@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	hridya@google.com, kernel-team@android.com
Subject: Re: [PATCH 3/3] binderfs_test: switch from /dev to /tmp as mountpoint
Date: Thu, 12 Mar 2020 16:54:25 -0700	[thread overview]
Message-ID: <202003121653.4BC2D43@keescook> (raw)
In-Reply-To: <20200312131531.3615556-3-christian.brauner@ubuntu.com>

On Thu, Mar 12, 2020 at 02:15:31PM +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.
> 
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Seems good. (Though would a dynamic location be better?
mkstemp()-style?)

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

-Kees

> ---
>  .../filesystems/binderfs/binderfs_test.c      | 30 +++++++++----------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
> index 313ffad15614..d6e61998d20a 100644
> --- a/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
> +++ b/tools/testing/selftests/filesystems/binderfs/binderfs_test.c
> @@ -76,7 +76,7 @@ static void __do_binderfs_test(void)
>  
>  	change_mountns();
>  
> -	ret = mkdir("/dev/binderfs", 0755);
> +	ret = mkdir("/tmp/binderfs", 0755);
>  	if (ret < 0) {
>  		if (errno != EEXIST)
>  			ksft_exit_fail_msg(
> @@ -86,13 +86,13 @@ static void __do_binderfs_test(void)
>  		keep = true;
>  	}
>  
> -	ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
> +	ret = mount(NULL, "/tmp/binderfs", "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");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_skip(
>  			"The Android binderfs filesystem is not available\n");
>  	}
> @@ -102,7 +102,7 @@ static void __do_binderfs_test(void)
>  
>  	memcpy(device.name, "my-binder", strlen("my-binder"));
>  
> -	fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
> +	fd = open("/tmp/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
>  	if (fd < 0)
>  		ksft_exit_fail_msg(
>  			"%s - Failed to open binder-control device\n",
> @@ -113,7 +113,7 @@ static void __do_binderfs_test(void)
>  	close(fd);
>  	errno = saved_errno;
>  	if (ret < 0) {
> -		keep ? : rmdir_protect_errno("/dev/binderfs");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_fail_msg(
>  			"%s - Failed to allocate new binder device\n",
>  			strerror(errno));
> @@ -126,9 +126,9 @@ static void __do_binderfs_test(void)
>  	/* binder device allocation test passed */
>  	ksft_inc_pass_cnt();
>  
> -	fd = open("/dev/binderfs/my-binder", O_CLOEXEC | O_RDONLY);
> +	fd = open("/tmp/binderfs/my-binder", O_CLOEXEC | O_RDONLY);
>  	if (fd < 0) {
> -		keep ? : rmdir_protect_errno("/dev/binderfs");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_fail_msg("%s - Failed to open my-binder device\n",
>  				   strerror(errno));
>  	}
> @@ -138,7 +138,7 @@ static void __do_binderfs_test(void)
>  	close(fd);
>  	errno = saved_errno;
>  	if (ret < 0) {
> -		keep ? : rmdir_protect_errno("/dev/binderfs");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_fail_msg(
>  			"%s - Failed to open perform BINDER_VERSION request\n",
>  			strerror(errno));
> @@ -150,9 +150,9 @@ static void __do_binderfs_test(void)
>  	/* binder transaction with binderfs binder device passed */
>  	ksft_inc_pass_cnt();
>  
> -	ret = unlink("/dev/binderfs/my-binder");
> +	ret = unlink("/tmp/binderfs/my-binder");
>  	if (ret < 0) {
> -		keep ? : rmdir_protect_errno("/dev/binderfs");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_fail_msg("%s - Failed to delete binder device\n",
>  				   strerror(errno));
>  	}
> @@ -160,12 +160,12 @@ static void __do_binderfs_test(void)
>  	/* binder device removal passed */
>  	ksft_inc_pass_cnt();
>  
> -	ret = unlink("/dev/binderfs/binder-control");
> +	ret = unlink("/tmp/binderfs/binder-control");
>  	if (!ret) {
> -		keep ? : rmdir_protect_errno("/dev/binderfs");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_fail_msg("Managed to delete binder-control device\n");
>  	} else if (errno != EPERM) {
> -		keep ? : rmdir_protect_errno("/dev/binderfs");
> +		keep ? : rmdir_protect_errno("/tmp/binderfs");
>  		ksft_exit_fail_msg(
>  			"%s - Failed to delete binder-control device but exited with unexpected error code\n",
>  			strerror(errno));
> @@ -175,8 +175,8 @@ static void __do_binderfs_test(void)
>  	ksft_inc_xfail_cnt();
>  
>  on_error:
> -	ret = umount2("/dev/binderfs", MNT_DETACH);
> -	keep ?: rmdir_protect_errno("/dev/binderfs");
> +	ret = umount2("/tmp/binderfs", MNT_DETACH);
> +	keep ?: rmdir_protect_errno("/tmp/binderfs");
>  	if (ret < 0)
>  		ksft_exit_fail_msg("%s - Failed to unmount binderfs\n",
>  				   strerror(errno));
> -- 
> 2.25.1
> 

-- 
Kees Cook