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Date: Thu, 18 Nov 2021 10:30:32 -0800
From: Casey Schaufler <>
To: Kees Cook <>
Cc: Alexander Popov <>,
 Steven Rostedt <>,
 Linus Torvalds <>,
 Lukas Bulwahn <>, Jonathan Corbet <>,
 Paul McKenney <>, Andrew Morton
 <>, Thomas Gleixner <>,
 Peter Zijlstra <>, Joerg Roedel <>,
 Maciej Rozycki <>, Muchun Song <>,
 Viresh Kumar <>, Robin Murphy <>,
 Randy Dunlap <>, Lu Baolu <>,
 Petr Mladek <>, Luis Chamberlain <>,
 Wei Liu <>, John Ogness <>,
 Andy Shevchenko <>,
 Alexey Kardashevskiy <>,
 Christophe Leroy <>, Jann Horn
 <>, Greg Kroah-Hartman <>,
 Mark Rutland <>, Andy Lutomirski <>,
 Dave Hansen <>, Will Deacon <>,
 Ard Biesheuvel <>, Laura Abbott <>,
 David S Miller <>, Borislav Petkov <>,
 Arnd Bergmann <>, Andrew Scull <>,
 Marc Zyngier <>, Jessica Yu <>,
 Iurii Zaikin <>,
 Rasmus Villemoes <>, Wang Qing <>,
 Mel Gorman <>,
 Mauro Carvalho Chehab <>,
 Andrew Klychkov <>,
 Mathieu Chouquet-Stringer <>,
 Daniel Borkmann <>, Stephen Kitt <>,
 Stephen Boyd <>,
 Thomas Bogendoerfer <>,
 Mike Rapoport <>, Bjorn Andersson
 Kernel Hardening <>,,
 "open list:DOCUMENTATION" <>,
 linux-arch <>,
 Linux Kernel Mailing List <>,
 linux-fsdevel <>,,,,, Shuah Khan <>,
 Casey Schaufler <>
Subject: Re: [PATCH v2 0/2] Introduce the pkill_on_warn parameter

On 11/18/2021 9:32 AM, Kees Cook wrote:
> On Tue, Nov 16, 2021 at 11:00:23AM -0800, Casey Schaufler wrote:
>> On 11/16/2021 10:41 AM, Kees Cook wrote:
>>> On Tue, Nov 16, 2021 at 12:12:16PM +0300, Alexander Popov wrote:
>>>> What if the Linux kernel had a LSM module responsible for error handling policy?
>>>> That would require adding LSM hooks to BUG*(), WARN*(), KERN_EMERG, etc.
>>>> In such LSM policy we can decide immediately how to react on the kernel error.
>>>> We can even decide depending on the subsystem and things like that.
>>> That would solve the "atomicity" issue the WARN tracepoint solution has,
>>> and it would allow for very flexible userspace policy.
>>> I actually wonder if the existing panic_on_* sites should serve as a
>>> guide for where to put the hooks. The current sysctls could be replaced
>>> by the hooks and a simple LSM.
>> Do you really want to make error handling a "security" issue?
>> If you add security_bug(), security_warn_on() and the like
>> you're begging that they be included in SELinux (AppArmor) policy.
>> BPF, too, come to think of it. Is that what you want?
> Yeah, that is what I was thinking. This would give the LSM a view into
> kernel state, which seems a reasonable thing to do. If system integrity
> is compromised, an LSM may want to stop trusting things.

How are you planning to communicate the security relevance of the
warning to the LSM? I don't think that __FILE__, __LINE__ or __func__
is great information to base security policy on. Nor is a backtrace.

> A dedicated error-handling LSM could be added for those hooks that
> implemented the existing default panic_on_* sysctls, and could expand on
> that logic for other actions.

I can see having an interface like LSM for choosing a bug/warn policy.
I worry about expanding the LSM hook list for a case where I would
hope no existing LSM would use them, and the new LSM doesn't use any
of the existing hooks.

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