[ubuntu-hardened] fs: suid_dumpable=2 and a security issue (gain root privileges).

[Kees Cook]

On Thu, Jan 14, 2016 at 01:17:07PM +0100, daniel curtis wrote:
> Hello.
> 
> Sorry for asking an question on a thread, which seems to be "solved". I
> would only know if setting 'fs.suid_dumpable' to '2' (which is default
> value in Ubuntu 12.04 LTS) is secure? It seems that with mode '1' (debug),
> the core dump is owned by the current user and no security is applied.
> 
> Mode '2' (sudisafe) - default value. For security reasons core dumps in
> this mode will not overwrite one another or other files etc. But according
> to this article [1] mode '2' is no longer allowed, right? Mentioned article
> and patch introduces mode '3' (pipeforced), but it can't be set in Ubuntu
> 12.04, for example, via 'sysctl.conf' file with an error:
> 
> >> "Invalid argument" setting key "fs.suid_dumpable"
> 
> So, according to all of this, I would like to ask if mode '2' is okay or it
> is better to set this to e.g. '0'?
> 
> Thanks, best regards.
> _____________________
> [1] https://lwn.net/Articles/503315/

The article showed an early draft idea about how to fix it. It was,
instead, fixed such that "2" is safe as-is.

-Kees

-- 
Kees Cook