| Posted | Nick | Remark | |
|---|---|---|---|
| #openstack-nova - 2018-06-01 | |||
| 17:58:05 | SpamapS | mnaser: yeah we're disabling the feature, and likely won't re-enable it until it also re-enables compute nodes automatically. But I figure there are likely Nova users out there that have it enabled, and are vulnerable to a malicious or even just poorly-configured user disabling all their compute nodes. | |
| 17:58:08 | superdan | SpamapS: well, we could do that, but when I brought it up in the room, nobody wanted it to re-enable | |
| 17:58:17 | mnaser | superdan: agreed, it includes things like ports, i think i worked partially on this but i forgot what progress i had :( | |
| 17:59:27 | superdan | for what it's worth, | |
| 17:59:36 | jgwentworth | mnaser: yeah. I think we saw that it would quickly become whack-a-mole, so we didn't have a straightforward way to solve it. trying to whitelist a bunch of things is a mess | |
| 17:59:48 | superdan | anything that accidentally falls into the disable bucket are also things that generate retries, | |
| 18:00:02 | superdan | so a user that can abuse that can also generate a ton of extra churn in the system, being DoSish on its own | |
| 18:00:11 | superdan | should we CVE for having max_attempts>1? | |
| 18:00:21 | SpamapS | Anyway, there are two things I'd like to see happen and I'm happy to drive either or both. (1) Fix it so that it only increments on *specific* faults that are permanent failures on the compute node, instead of just a whitelist for exceptions to ignore. And (2) inform the user community of the danger they may be in. | |
| 18:00:43 | superdan | SpamapS: it already only increments for specific things | |
| 18:00:44 | superdan | SpamapS: it's just that set needs tweaking | |
| 18:00:57 | SpamapS | did you see the list harlowja made? | |
| 18:01:01 | mnaser | superdan:, SpamapS: http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-nova.2018-04-12.log.html | |
| 18:01:03 | mnaser | brief discussion there | |
| 18:01:07 | SpamapS | Those don't seem well thought out. | |
| 18:01:12 | SpamapS | And aren't explicitly listed. | |
| 18:01:23 | SpamapS | mnaser: indeed, I found that yesterday. | |
| 18:01:39 | superdan | well, part of the problem is that we convert stupid exceptions to stupid build results | |
| 18:01:48 | superdan | and it operates on the latter | |
| 18:02:01 | SpamapS | https://bugs.launchpad.net/nova/+bug/1774527 | |
| 18:02:02 | openstack | Launchpad bug 1742102 in OpenStack Compute (nova) "duplicate for #1774527 Simple user can disable compute" [High,In progress] - Assigned to Matt Riedemann (mriedem) | |
| 18:02:03 | SpamapS | has Josh's list | |
| 18:02:15 | mnaser | and then previous discussion here too http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-nova.2018-01-23.log.html#t2018-01-23T19:36:41 | |
| 18:02:30 | mnaser | but i have to get back to doing some $work stuff but yeah, we disabled it on ourside | |
| 18:02:39 | SpamapS | superdan: perhaps we shouldn't disable on stupid things? | |
| 18:02:48 | superdan | SpamapS: I think I've said I agree with that statement :) | |
| 18:02:57 | SpamapS | indeed | |
| 18:03:01 | superdan | how come you guys think this is CVEish and just filed a non-security bug for it? | |
| 18:03:14 | superdan | that kinda eliminates the supposed desire to make a big deal over it :) | |
| 18:03:30 | jgwentworth | superdan: they filed it as security but it's already known | |
| 18:03:48 | jgwentworth | so I'm not sure how that works. | |
| 18:03:55 | superdan | it's public, so not a security bug | |
| 18:04:03 | SpamapS | and agreed that if you can cause a bunch of retries you are already causing the cloud some slowness. But the compute nodes disable somewhat silently, and permanently, creating a far worse situation than just "it's slow now" | |
| 18:04:20 | jgwentworth | well, IMHO it should have been a security bug from the start, but the original bug reporter reported it as public | |
| 18:04:28 | SpamapS | We didn't actually think it was a security bug, just reporting "hey this broke our cloud" | |
| 18:04:38 | SpamapS | and then we debugged more and were like "zomg security" | |
| 18:04:43 | SpamapS | and then we found out there was already public knowledge | |
| 18:05:03 | superdan | SpamapS: you're going to DoS the first three nodes in your pack scenario | |
| 18:05:12 | superdan | if you're just hitting those | |
| 18:05:21 | superdan | so, anyway, | |
| 18:05:21 | mnaser | except if you boot with --num-instances 100 | |
| 18:05:39 | superdan | mnaser: well, true, but you're going for DoS so you don't do that if you're an attacker, right? | |
| 18:05:58 | superdan | anyway, I'd really like to fix the thing and not rip it out, | |
| 18:06:08 | superdan | but if people want to disable it by default for now, that's cool | |
| 18:06:12 | superdan | although I think that means we'll never fix it | |
| 18:06:17 | mnaser | maybe i should hush but nova doesn't even let us control the # to provide in --num-instances (and i'm agreeing that we clean it up rather than remove it) | |
| 18:06:30 | mnaser | so if you have enough quota you can --num-instances one-zillion | |
| 18:06:34 | SpamapS | I think the right fix is to pick *specific* build results that have high or absolute confidence are the fault of the compute node. | |
| 18:06:41 | superdan | mnaser: OMG CVE! :) | |
| 18:06:46 | mnaser | shhh its friday | |
| 18:06:47 | mnaser | we don't want that | |
| 18:06:58 | superdan | SpamapS: we do pick specific build results, that's the thing | |
| 18:07:09 | superdan | SpamapS: we convert _exceptions_ to build results in not the right way | |
| 18:07:18 | mnaser | anything that results in a rescheduled build will trigger that counter to increase i think | |
| 18:07:26 | SpamapS | How does an image too big for flavor failure land in that bucket then? | |
| 18:07:45 | SpamapS | Or a "failure to download image" | |
| 18:07:45 | mnaser | i think that's a bug that nova considers that a reschedule-able failure | |
| 18:08:04 | SpamapS | yeah see re-schedulable doesn't mean it's the compute node's fault. | |
| 18:08:10 | jgwentworth | I dunno, I do think it's worth an advisory to call this out because if any ol user could disable a lot of compute nodes by just making normal requests, it's a major problem | |
| 18:08:13 | mnaser | failure to download image could be that specific compute node cannot talk to glance | |
| 18:08:25 | mnaser | but it's a tricky weird thing to balance | |
| 18:08:27 | SpamapS | could be | |
| 18:08:30 | SpamapS | but you don't *know* | |
| 18:08:34 | mnaser | but if your glance is down then | |
| 18:08:44 | mnaser | all your compute nodes are going disabled | |
| 18:08:52 | jrollinhatin | SpamapS: looks like two members from the VMT are already aware of this bug and triaging how we notify about it; if you're looking to have it tagged with a CVE perhaps engage them instead (since they're the people that do that thing)? | |
| 18:09:07 | SpamapS | yeah if glance is down or just partitioned from 1/3 of your cloud for right now, you don't want that to take that entire part of the cloud down without also re-enabling it when it comes back or unpartitions. | |
| 18:09:08 | superdan | SpamapS: failure to download an image is pretty legit to disable, no? not flavor too small though, obviously | |
| 18:09:34 | superdan | yeah, if glance is down that's fair I guess | |
| 18:09:37 | SpamapS | jrollinhatin: ah good point. K, I've not actually driven a CVE before. | |
| 18:09:49 | SpamapS | superdan: failure to download an image is pretty ambiguous. | |
| 18:10:08 | SpamapS | And very likely to be temporary. | |
| 18:10:13 | superdan | SpamapS: it's easy for some computes to be unable to download images, partition like you said | |
| 18:10:39 | SpamapS | Like, to be able to really know where the fault is, you need something like Vitrage. | |
| 18:10:40 | superdan | SpamapS: so this came up as one compute node being unable to do basic stuff like that can _also_ take down your whole cloud because it attracts all new builds and fails them | |
| 18:10:56 | superdan | scientific cloud with no reschedules, pack mode, one compute node takes the whole thing down with it | |
| 18:11:15 | SpamapS | Right, so maybe the right thing is to split into two categories. | |
| 18:11:27 | SpamapS | Things to disable permanently for, and things to drop from retry list. | |
| 18:11:28 | superdan | maybe what we should have done is just make a weigher or filter based on the fail score | |
| 18:11:36 | SpamapS | or.. not retry | |
| 18:11:39 | mnaser | i like that idea | |
| 18:11:40 | SpamapS | but things to stop scheduling for | |
| 18:11:56 | superdan | mnaser: that's a fairly easy iteration from where we are | |
| 18:12:21 | SpamapS | This is where k8s's scheduler does something smarter. If they get a failure on a node, they retry for a while on that node, and then they start backing off from it.. scheduling less and less frequently to it. | |
| 18:12:27 | SpamapS | It's not disabled.. they keep trying it.. but less and less often. | |
| 18:13:05 | SpamapS | A weighter would be perfect. | |
| 18:13:17 | SpamapS | Just expose the consecutive failures counter and have a coeficient based on that. | |
| 18:13:35 | SpamapS | So as it gets higher, the node gets less and less attempts. | |
| 18:14:09 | jgwentworth | makes sense | |
| 18:14:11 | SpamapS | Arguably it should not reset to 0 on success, but just decrement. | |
| 18:14:22 | superdan | SpamapS: why? | |
| 18:14:29 | SpamapS | Flapping. | |
| 18:14:42 | superdan | SpamapS: you end up with a pretty hard to explain situation for why some compute nodes rarely get used, | |
| 18:14:54 | SpamapS | If you reset it to 0, you start dumping lots on it again, which may make it start failing again. | |
| 18:14:58 | superdan | which boils down to "it was partitioned for a long time a month ago and hasn't recovered" | |
| 18:15:15 | SpamapS | Yeah maybe there needs to be a time based decrementer too. | |
| 18:15:16 | superdan | so decrement by ten on each success | |
| 18:15:30 | SpamapS | Like, decrement by 1 every x seconds, and 1 every success. | |
| 18:15:33 | superdan | counter = min(0, counter - 10) | |
| 18:15:43 | superdan | SpamapS: you're building a complicated thing that generates DB traffic | |