Date: Fri, 27 Jul 2018 15:40:32 +0200 From: Jann Horn <jannh@...gle.com> To: Golden_Miller83@...tonmail.ch Cc: Steven Rostedt <rostedt@...dmis.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Greg KH <greg@...ah.com>, Kees Cook <keescook@...gle.com>, salyzyn@...roid.com, kernel list <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, kernel-team@...roid.com, stable@...r.kernel.org, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH] tracing: do not leak kernel addresses On Fri, Jul 27, 2018 at 2:07 PM Jordan Glover <Golden_Miller83@...tonmail.ch> wrote: > > 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 Then they shouldn't have access to debugfs at all, right?
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