Date: Tue, 1 Oct 2019 01:31:19 -0400 From: Paul Moore <paul@...l-moore.com> To: Kees Cook <keescook@...omium.org> Cc: Steve Grubb <sgrubb@...hat.com>, linux-kernel@...r.kernel.org, Jérémie Galarneau <jeremie.galarneau@...icios.com>, s.mesoraca16@...il.com, viro@...iv.linux.org.uk, dan.carpenter@...cle.com, akpm@...ux-foundation.org, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, kernel-hardening@...ts.openwall.com, linux-audit@...hat.com, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH] audit: Report suspicious O_CREAT usage On Mon, Sep 30, 2019 at 2:29 PM Kees Cook <keescook@...omium.org> wrote: > On Mon, Sep 30, 2019 at 09:50:00AM -0400, Steve Grubb wrote: > > On Thursday, September 26, 2019 11:31:32 AM EDT Paul Moore wrote: > > > On Wed, Sep 25, 2019 at 5:02 PM Kees Cook <keescook@...omium.org> wrote: > > > > This renames the very specific audit_log_link_denied() to > > > > audit_log_path_denied() and adds the AUDIT_* type as an argument. This > > > > allows for the creation of the new AUDIT_ANOM_CREAT that can be used to > > > > report the fifo/regular file creation restrictions that were introduced > > > > in commit 30aba6656f61 ("namei: allow restricted O_CREAT of FIFOs and > > > > regular files"). Without this change, discovering that the restriction > > > > is enabled can be very challenging: > > > > https://lore.kernel.org/lkml/CA+jJMxvkqjXHy3DnV5MVhFTL2RUhg0WQ-XVFW3ngDQO > > > > dkFq0PA@...l.gmail.com > > > > > > > > Reported-by: Jérémie Galarneau <jeremie.galarneau@...icios.com> > > > > Signed-off-by: Kees Cook <keescook@...omium.org> > > > > --- > > > > This is not a complete fix because reporting was broken in commit > > > > 15564ff0a16e ("audit: make ANOM_LINK obey audit_enabled and > > > > audit_dummy_context") > > > > which specifically goes against the intention of these records: they > > > > should _always_ be reported. If auditing isn't enabled, they should be > > > > ratelimited. > > > > > > > > Instead of using audit, should this just go back to using > > > > pr_ratelimited()? > > > > > > I'm going to ignore the rename and other aspects of this patch for the > > > moment so we can focus on the topic of if/when/how these records > > > should be emitted by the kernel. > > > > > > Unfortunately, people tend to get very upset if audit emits *any* > > > records when they haven't explicitly enabled audit, the significance > > > of the record doesn't seem to matter, which is why you see patches > > > like 15564ff0a16e ("audit: make ANOM_LINK obey audit_enabled and > > > audit_dummy_context"). We could consider converting some records to > > > printk()s, rate-limited or not, but we need to balance this with the > > > various security certifications which audit was created to satisfy. > > > In some cases a printk() isn't sufficient. > > > > > > Steve is probably the only one who really keeps track of the various > > > auditing requirements of the different security certifications; what > > > say you Steve on this issue with ANOM_CREAT records? > > > > Common Criteria and other security standards I track do not call out for > > anomoly detection. So, there are no requirements on this. That said, we do > > have other anomaly detections because they give early warning that something > > strange is happening. I think adding this event is a nice improvement as long > > as it obeys audit_enabled before emitting an event - for example, look at the > > AUDIT_ANOM_ABEND event. > > Okay, so the patch is good as-is? (The "report things always" issue I > will deal with separately. For now I'd just like to gain this anomaly > detection corner case...) > > Paul, what do you see as next steps here? I'll reply back on the original post so I can more easily comment on the details of patch. -- paul moore www.paul-moore.com
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