Re: [PATCH] exit: Put an upper limit on how often we can oops

[Kees Cook <keescook@chromium.org>]

On Mon, Nov 07, 2022 at 10:48:20PM +0100, Jann Horn wrote:
> On Mon, Nov 7, 2022 at 10:15 PM Solar Designer <solar@openwall.com> wrote:
> > On Mon, Nov 07, 2022 at 09:13:17PM +0100, Jann Horn wrote:
> > > +oops_limit
> > > +==========
> > > +
> > > +Number of kernel oopses after which the kernel should panic when
> > > +``panic_on_oops`` is not set.
> >
> > Rather than introduce this separate oops_limit, how about making
> > panic_on_oops (and maybe all panic_on_*) take the limit value(s) instead
> > of being Boolean?  I think this would preserve the current behavior at
> > panic_on_oops = 0 and panic_on_oops = 1, but would introduce your
> > desired behavior at panic_on_oops = 10000.  We can make 10000 the new
> > default.  If a distro overrides panic_on_oops, it probably sets it to 1
> > like RHEL does.
> >
> > Are there distros explicitly setting panic_on_oops to 0?  If so, that
> > could be a reason to introduce the separate oops_limit.
> >
> > I'm not advocating one way or the other - I just felt this should be
> > explicitly mentioned and decided on.
> 
> I think at least internally in the kernel, it probably works better to
> keep those two concepts separate? For example, sparc has a function
> die_nmi() that uses panic_on_oops to determine whether the system
> should panic when a watchdog detects a lockup.

Internally, yes, the kernel should keep "panic_on_oops" to mean "panic
_NOW_ on oops?" but I would agree with Solar -- this is a counter as far
as userspace is concerned. "Panic on Oops" after 1 oops, 2, oopses, etc.
I would like to see this for panic_on_warn too, actually.

-- 
Kees Cook