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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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