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

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Date:   Fri, 27 Jul 2018 08:07:13 -0400
From:   Jordan Glover <Golden_Miller83@...tonmail.ch>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        "greg@...ah.com" <greg@...ah.com>, Kees Cook <keescook@...gle.com>,
        "salyzyn@...roid.com" <salyzyn@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] tracing: do not leak kernel addresses

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

> On Thu, 26 Jul 2018 09:52:11 -0700
> Nick Desaulniers ndesaulniers@...gle.com 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

Jordan