linux-hardening - Re: [PATCH v8 0/8] Fork brute force attack mitigation

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Date:   Tue, 8 Jun 2021 16:19:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     John Wood <john.wood@....com>
Cc:     Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Arnd Bergmann <arnd@...db.de>, Andi Kleen <ak@...ux.intel.com>,
        valdis.kletnieks@...edu,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v8 0/8] Fork brute force attack mitigation

On Sat, Jun 05, 2021 at 05:03:57PM +0200, John Wood wrote:
> [...]
> the kselftest to avoid the detection ;) ). So, in this version, to track
> all the statistical data (info related with application crashes), the
> extended attributes feature for the executable files are used. The xattr is
> also used to mark the executables as "not allowed" when an attack is
> detected. Then, the execve system call rely on this flag to avoid following
> executions of this file.

I have some concerns about this being actually usable and not creating
DoS situations. For example, let's say an attacker had found a hard-to-hit
bug in "sudo", and starts brute forcing it. When the brute LSM notices,
it'll make "sudo" unusable for the entire system, yes?

And a reboot won't fix it, either, IIUC.

It seems like there is a need to track "user" running "prog", and have
that be timed out. Are there use-cases here where that wouldn't be
sufficient?

-Kees

-- 
Kees Cook