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Date:   Tue, 8 Jun 2021 16:19:31 -0700
From:   Kees Cook <>
To:     John Wood <>
Cc:     Jann Horn <>, Jonathan Corbet <>,
        James Morris <>,
        "Serge E. Hallyn" <>,
        Shuah Khan <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,, "H. Peter Anvin" <>,
        Arnd Bergmann <>, Andi Kleen <>,,
        Greg Kroah-Hartman <>,
        Randy Dunlap <>,
        Andrew Morton <>,,,,,,,
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


Kees Cook

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