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Subject: Re: [PATCH v8 0/8] Fork brute force attack mitigation
To:     Kees Cook <keescook@chromium.org>, John Wood <john.wood@gmx.com>
Cc:     Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Arnd Bergmann <arnd@arndb.de>, valdis.kletnieks@vt.edu,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-hardening@vger.kernel.org,
        kernel-hardening@lists.openwall.com
References: <20210605150405.6936-1-john.wood@gmx.com>
 <202106081616.EC17DC1D0D@keescook>
From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <cbfd306b-6e37-a697-ebdb-4a5029d36583@linux.intel.com>
Date:   Tue, 8 Jun 2021 16:38:15 -0700
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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.

-Andi