Date: Wed, 29 Nov 2017 01:36:39 -0500 From: Theodore Ts'o <tytso@....edu> To: Kees Cook <keescook@...omium.org> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Djalal Harouni <tixxdz@...il.com>, Jonathan Corbet <corbet@....net>, James Morris <james.l.morris@...cle.com>, LSM List <linux-security-module@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Geo Kozey <geokozey@...lfence.com>, Tycho Andersen <tycho@...ker.com> Subject: Re: Re: [PATCH v5 next 5/5] net: modules: use request_module_cap() to load 'netdev-%s' modules On Tue, Nov 28, 2017 at 04:18:59PM -0800, Kees Cook wrote: > There's also a difference between immutable CONFIG options that cannot > be disabled at runtime, those that can, global sysctls, per-namespace > controls, etc etc. The kernel is all about providing admins with knobs > to tweak their performance and security. Suddenly being told that we > can't create optional improvements is very odd. I just think that tweakable knobs are mostly pointless. From my experience the number of sysadmins that adjust knobs is ***tiny***. Put another way, the effort to determine whether tweaking a knob will result in breakages or will be safe is as much work as creating a white list of modules that are allowed to be loaded.  And I say that having providing a lot of knobs for ext4. :-) This is why some on the kernel-hardening list have argued for making the default to be opt-out, which means some users will be breaken (and their answer to that seems to be, "oh well --- gotta break some eggs to make an omlette". Sucks if you're one of the eggs, though.) And I don't see how systemd magically means no one will be broken. If you have a non-root process trying to invoke a line discpline which has to be loaded as a module, if you flip the switch, that process will be broken. How does using systemd make the problem go away? - Ted
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