[PATCH 0/6] File Sealing & memfd_create()

[Colin Walters]

On Thu, Apr 10, 2014 at 3:15 PM, Andy Lutomirski <luto at amacapital.net> 
wrote:
> 
> 
> COW links can do this already, I think.  Of course, you'll have to 
> use a
> filesystem that supports them.

COW is nice if the filesystem supports them, but my userspace code 
needs to be filesystem agnostic.  Because of that, the design for 
userspace simply doesn't allow arbitrary writes.

Instead, I have to painfully audit every rpm %post/dpkg postinst type 
script to ensure they break hardlinks, and furthermore only allow 
executing scripts that are known to do so.

But I think even in a btrfs world it'd still be useful to mark files as 
content-immutable.