Re: [PATCH] tracing: do not leak kernel addresses

From: Jordan Glover
Date: Fri Jul 27 2018 - 08:07:26 EST

On July 27, 2018 12:15 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Thu, 26 Jul 2018 09:52:11 -0700
> Nick Desaulniers ndesaulniers@xxxxxxxxxx wrote:
> > See the section "Kernel addresses" in
> > Documentation/security/self-protection. IIRC, the issue is that a
> > process may have CAP_SYSLOG but not necessarily CAP_SYS_ADMIN (so it
> > can read dmesg, but not necessarily issue a sysctl to change
> > kptr_restrict), get compromised and used to leak kernel addresses,
> > which can then be used to defeat KASLR.
> But the code doesn't go to dmesg. It's only available
> via /sys/kernel/debug/tracing/printk_formats which is only available
> via root. Nobody else has access to that directory.
> -- Steve

I think the point was that when we take capabilities into account the root
privileges aren't unequivocal anymore. The 'root' owned process with only
'CAP_SYSLOG' shouldn't have access to /sys/kernel/debug/tracing/printk_formats