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Date:	Sun, 3 Mar 2013 10:30:12 -0800
From:	Kees Cook <>
To:	"Eric W. Biederman" <>
Cc:	"Serge E. Hallyn" <>,
	LKML <>,
	Serge Hallyn <>,
	Brad Spengler <>,
	Al Viro <>,
	Eric Paris <>,
	Rusty Russell <>,
	"" <>
Subject: Re: [RFC][PATCH] fs: Limit sys_mount to only loading filesystem modules.

On Sun, Mar 3, 2013 at 2:14 AM, Eric W. Biederman <> 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.
> Using aliases means user space can control the policy of which
> filesystem modules are auto-loaded by editing /etc/modprobe.d/*.conf
> with blacklist and alias directives.  Allowing simple, safe,
> well understood work-arounds to known problematic software.
> This also addresses a rare but unfortunate problem where the filesystem
> name is not the same as it's module name and module auto-loading
> would not work.  While writing this patch I saw a handful of such
> cases.  The most significant being autofs that lives in the module
> autofs4.
> Signed-off-by: "Eric W. Biederman" <>

Acked-by: Kees Cook <>

Kees Cook
Chrome OS Security
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