Re: [devel] [PATCH hasher-priv v1 0/3] Make a daemon from the hasher-priv

["Dmitry V. Levin" <ldv@altlinux.org>]

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On Sun, Dec 15, 2019 at 11:50:13AM +0300, Alexey Tourbin wrote:
> On Fri, Dec 13, 2019 at 2:42 PM Alex Gladkov <legion@altlinux.ru> wrote:
> > The hasher-priv is a SUID utility. This is not good. Separation of the
> > server and client parts will allow us to remove SUID flag.
> 
> Removing the SUID flag shouldn't be an end in itself. You're still
> running a process with root privileges which serves user requests.
> It's the same, except that instead of the SUID flag, the process just
> starts as root.  So you are not improving privilege separation or
> something, you are only limiting the ability of the user to tamper
> with the SUID binary. And tampering with the binary should be
> pointless anyway (unless glibc is faulty and permits arbitrary code
> injection, etc.).

While turning a suid root executable into a daemon doesn't automagically
make everything more secure, it's an important move in the right direction.

Firstly, the attack surface of a suid root executable is larger than
of the equivalent root daemon on the other side of a unix domain socket,
so this change narrows the attack surface.

Secondly, this change opens the way for more elaborate privilege separation.

Thirdly, it makes hasher available for PR_SET_NO_NEW_PRIVS'ed
processes (e.g. self-seccomp'ed) that cannot make use of suid executables.


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ldv

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