Date: Fri, 27 Jul 2018 11:41:05 -0700 From: Mark Salyzyn <salyzyn@...gle.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Nick Desaulniers <ndesaulniers@...gle.com>, Jann Horn <jannh@...gle.com>, Golden_Miller83@...tonmail.ch, greg@...ah.com, Kees Cook <keescook@...gle.com>, Mark Salyzyn <salyzyn@...roid.com>, LKML <linux-kernel@...r.kernel.org>, mingo@...hat.com, Android Kernel Team <kernel-team@...roid.com>, stable@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH] tracing: do not leak kernel addresses Any system can chose to change the permissions of a sysfs node, default, DAC (and MAC) is just layers of multi-level security (or lack thereof). As well intentioned as a default DAC is in the kernel, leaking kernel addresses is still an attack surface that we want to close tightly. For instance on Android: chmod 0755 /sys/kernel/debug/tracing is in the common init.rc file ... If DAC has been adjusted at runtime to permit access to the node, I would think that if the caller does not have all the credentials/capabilities, we do want the addresses to be abstracted by the kernel. -- Mark On Fri, Jul 27, 2018 at 11:31 AM, Steven Rostedt <rostedt@...dmis.org> wrote: > On Fri, 27 Jul 2018 11:13:51 -0700 > Nick Desaulniers <ndesaulniers@...gle.com> wrote: > > > I found the internal bug report (reported Jan '17, you'll have to > > forgive me if my memory of the issue is hazy, or if the fix used at > > the time wasn't perfect), which was reported against the Nexus 6. > > >From the report, it was possible to `cat > > /sys/kernel/debug/tracing/printk_formats` without being root, which I > > can't do on my workstations much more modern kernel (Nexus 6 was > > 3.10). So I guess the question is what governs access to files below > > /sys/kernel/debug, and why was it missing from those kernels? I > > assume some check was added, but either not backported to 3.10 stable > > (or more likely not pulled in to Nexus 6's kernel through stable; > > Android is now in a much better place for that kind of issue). > > As of commit 82aceae4f0d4 ("debugfs: more tightly restrict default > mount mode") /sys/kernel/debug has been default mounted as 0700 (root > only). But that was introduced in 3.7. Not sure why your 3.10 kernel > didn't have that. Perhaps there's another commit that fixed > permissions not being inherited? > > -- Steve > > -- > You received this message because you are subscribed to the Google Groups > "kernel-team" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to kernel-team+unsubscribe@...roid.com. > > Content of type "text/html" skipped
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