[PATCH 2/2] fs: Limit sys_mount to only request filesystem modules.

[Kees Cook]

On Tue, Mar 5, 2013 at 11:06 AM, Kay Sievers <kay at vrfy.org> wrote:
> On Mon, Mar 4, 2013 at 8:51 AM, Eric W. Biederman <ebiederm at xmission.com> wrote:
>>
>> Modify the request_module to prefix the file system type with "fs-"
>> and add aliases to all of the filesystems that can be built as modules
>> to match.
>>
>> A common practice is to build all of the kernel code and leave code
>> that is not commonly needed as modules, with the result that many
>> users are exposed to any bug anywhere in the kernel.
>>
>> Looking for filesystems with a fs- prefix limits the pool of possible
>> modules that can be loaded by mount to just filesystems trivially
>> making things safer with no real cost.
>
> '-' is a commonly used part of a module name, and does not mix well
> with ramdom user provided names.
>
> We usually use ':' as the prefix separator for modaliases, when
> user-supplied strings are prefixed with the subsystem.
>
> I think it would be nicer to change that, and I'm sure some creative
> guy calls the next filesystem of the month fs-$something :)

The precedent is "-". "netdev-" "pf-net-" etc. Naming something
fs-$something is fine as long as it's actually a filesystem. :)

-Kees

-- 
Kees Cook
Chrome OS Security