Date: Wed, 9 Jun 2021 09:52:29 -0700 From: Kees Cook <keescook@...omium.org> To: Andi Kleen <ak@...ux.intel.com> Cc: John Wood <john.wood@....com>, 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>, 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 Tue, Jun 08, 2021 at 04:38:15PM -0700, Andi Kleen wrote: > > On 6/8/2021 4:19 PM, Kees Cook wrote: > > 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. > > > The whole point of the mitigation is to trade potential attacks against DOS. > > If you're worried about DOS the whole thing is not for you. Right, but there's no need to make a system unusable for everyone else. There's nothing here that relaxes the defense (i.e. stop spawning apache for 10 minutes). Writing it to disk with nothing that undoes it seems a bit too much. :) -- Kees Cook
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