Date: Fri, 9 Apr 2021 16:29:33 +0200 From: John Wood <john.wood@....com> To: Valdis Klētnieks <valdis.kletnieks@...edu>, Andi Kleen <ak@...ux.intel.com> Cc: John Wood <john.wood@....com>, kernelnewbies@...nelnewbies.org, Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com Subject: Re: Notify special task kill using wait* functions Hi Valdis and Andi. Thanks for your comments. On Wed, Apr 07, 2021 at 06:51:48PM -0700, Andi Kleen wrote: > > I didn't even finish the line that starts "From now on.." before I started > > wondering "How can I abuse this to hang or crash a system?" And it only took > > me a few seconds to come up with an attack. All you need to do is find a way to > > sigsegv /bin/bash... and that's easy to do by forking, excecve /bin/bash, and > > then use ptrace() to screw the child process's stack and cause a sigsegv. > > > > Say goodnight Gracie... > > Yes there is certainly DoS potential, but that's kind of inevitable > for the proposal. It's a trade between allowing attacks and allowing DoS, > with the idea that a DoS is more benign. > > I'm more worried that it doesn't actually prevent the attacks > unless we make sure systemd and other supervisor daemons understand it, > so that they don't restart. I'm working on it. I will send a formal proposal in the next version. > Any caching of state is inherently insecure because any caches of limited > size can be always thrashed by a purposeful attacker. I suppose the > only thing that would work is to actually write something to the > executable itself on disk, but of course that doesn't always work either. I'm also working on this. In the next version I will try to find a way to prevent brute force attacks through the execve system call with more than one level of forking. > -Andi Again, thank you very much. John Wood
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