oss-sec mailing list archives
Re: lockdown bypass on mainline kernel for loading unsigned modules
From: "Jason A. Donenfeld" <Jason () zx2c4 com>
Date: Mon, 15 Jun 2020 11:28:57 -0600
On 6/15/20, Jann Horn <jannh () google com> wrote:
On Mon, Jun 15, 2020 at 6:24 PM John Haxby <john.haxby () oracle com> wrote:On 15 Jun 2020, at 11:26, Jason A. Donenfeld <Jason () zx2c4 com> wrote: Yesterday, I found a lockdown bypass in Ubuntu 18.04's kernel using ACPI table tricks via the efi ssdt variable [1]. Today I found another one that's a bit easier to exploit and appears to be unpatched on mainline, using acpi_configfs to inject an ACPI table. The tricks are basically the same as the first one, but this one appears to be unpatched, at least on my test machine. Explanation is in the header of the PoC: https://git.zx2c4.com/american-unsigned-language/tree/american-unsigned-language-2.sh I need to get some sleep, but if nobody posts a patch in the meanwhile, I'll try to post a fix tomorrow. Jason [1] https://www.openwall.com/lists/oss-security/2020/06/14/1This looks CVE-worthy. Are you going to ask for a CVE for it?Does it really make sense to dole out CVEs for individual lockdown bypasses when various areas of the kernel (such as filesystems and BPF) don't see root->kernel privilege escalation issues as a problem? It's not like applying the fix for this one issue is going to make systems meaningfully safer.
Indeed, I'm more or less of the same mind: lockdown is kind of a best-effort thing at the moment, and it'd be crazy to rely on it, considering various bypasses and differing attitudes on the security model from different subsystems. This acpi bypass is a bug, maybe, but it doesn't feel like a "real" security bug, because I'm not sure why this would be a feature somebody would want to lean on at this point in time. I wrote a PoC for this one rather than others because it seemed fun and technically interesting to poke around with acpi in this way, not because it's particularly rare or something.
Current thread:
- lockdown bypass on mainline kernel for loading unsigned modules Jason A. Donenfeld (Jun 15)
- Re: lockdown bypass on mainline kernel for loading unsigned modules John Haxby (Jun 15)
- Re: lockdown bypass on mainline kernel for loading unsigned modules Jann Horn (Jun 15)
- Re: lockdown bypass on mainline kernel for loading unsigned modules Jason A. Donenfeld (Jun 15)
- Re: lockdown bypass on mainline kernel for loading unsigned modules Jann Horn (Jun 15)
- Re: lockdown bypass on mainline kernel for loading unsigned modules Jason A. Donenfeld (Jun 15)
- Re: lockdown bypass on mainline kernel for loading unsigned modules John Haxby (Jun 15)