Lua: Fix `limit_except` returning 503. #11860

ZJfans · 2024-08-24T18:33:26Z

What this PR does / why we need it:

Using limit_except GET { deny all; } together with location = / { return 403; } , When the request is POST ，results in 503, instead of 403.
This issue involves the ngx_http_core_module.c module of Nginx. When the limit_except directive is used, variables set within a location block cannot be accessed. Currently, the balancer.rewrite() in nginx.conf relies on the proxy_upstream_name variable, which leads to a failure in obtaining the balancer and results in a 503 error. However, it should actually return a 403 error.
If you need more details please let me know

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
CVE Report (Scanner found CVE and adding report)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation only

Which issue/s this PR fixes

fixes #11742

How Has This Been Tested?

kind: Ingress
metadata:
  name: foo-ingress
  namespace: default
  annotations:
    nginx.ingress.kubernetes.io/configuration-snippet: limit_except GET { deny all; }
    nginx.ingress.kubernetes.io/server-snippet: |
      location  =/ {
        return 403;
      }
spec:
  ingressClassName: nginx
  rules:
  - host:
    http:
      paths:
      - path: /foo
        pathType: Prefix
        backend:
          service:
            name: foo-service
            port:
              number: 8080

curl -X POST http://1xx.xxx.xxx.xx:32080/foo

<html>
<head><title>503 Service Temporarily Unavailable</title></head>
<body>
<center><h1>503 Service Temporarily Unavailable</h1></center>
<hr><center>nginx</center>
</body>
</html>

Checklist:

My change requires a change to the documentation.
I have updated the documentation accordingly.
I've read the CONTRIBUTION guide
I have added unit and/or e2e tests to cover my changes.
All new and existing tests passed.

k8s-ci-robot · 2024-08-24T18:33:34Z

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linux-foundation-easycla · 2024-08-24T18:33:34Z

The committers listed above are authorized under a signed CLA.

✅ login: ZJfans / name: zhangjie (8104914, 72ff20f)

k8s-ci-robot · 2024-08-24T18:33:34Z

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k8s-ci-robot · 2024-08-24T18:33:35Z

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Gacko · 2024-08-25T06:04:42Z

We are currently trying to refrain from snippets and/or Lua at all, so I'm not sure if it makes sense to further extend these parts of the codebase.

@strongjz @rikatz @tao12345666333 WDYT?

ZJfans · 2024-08-25T10:06:12Z

We are currently trying to refrain from snippets and/or Lua at all, so I'm not sure if it makes sense to further extend these parts of the codebase.

@strongjz @rikatz @tao12345666333 WDYT?

Sorry, I didn't realize that Lua is being removed at the moment. If this is not necessary, we can close this request.

Gacko · 2024-08-25T10:35:01Z

Lua is not being removed, but reduced and we'd like to replace it by NJS (https://nginx.org/en/docs/njs) or something similar in the long run - if even required.

Currently I can not tell if your PR is just a fix or a feature as I'm not so deep into Lua, yet. I can only tell that - what you already noticed - we'd like to reduce it and - for security reasons - get rid of snippets. Which brings me back to the "feature or fix" question as this issue only occurs in conjunction with snippets, right?

ZJfans · 2024-08-25T12:29:03Z

It's a fix, this is my analysis, not English, need translation (https://zjfans.github.io/2024/08/25/Problems%20with%20ingress-nginx%20using%20limit_except/)

Gacko · 2024-08-26T21:54:49Z

Do I understand correctly, that in case of a forbidden request method NGINX does not enter the location block and therefore does not set the proxy upstream name, but still enters the get_balancer function? Because then we should rather just do the same nil check as a few lines below and also return nil instead of answering the request with 403.

At least this Lua function does not seem to be the right place for generating the final response to me.

Gacko · 2024-08-26T21:56:24Z

/triage accepted
/kind bug
/priority backlog
/hold

Gacko · 2024-08-26T21:56:31Z

/cherry-pick release-1.10

Gacko · 2024-08-26T21:56:33Z

/cherry-pick release-1.11

k8s-infra-cherrypick-robot · 2024-08-26T21:56:33Z

@Gacko: once the present PR merges, I will cherry-pick it on top of release-1.10 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.10

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

k8s-infra-cherrypick-robot · 2024-08-26T21:56:34Z

@Gacko: once the present PR merges, I will cherry-pick it on top of release-1.11 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.11

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

Gacko · 2024-08-26T21:57:03Z

/ok-to-test

Gacko

Please also add appropriate tests for what you're trying to fix.

rikatz · 2024-08-26T23:48:18Z

I would like as well an e2e test for this situation returning the right behavior.

ZJfans · 2024-08-27T02:04:23Z

Do I understand correctly, that in case of a forbidden request method NGINX does not enter the location block and therefore does not set the proxy upstream name, but still enters the get_balancer function? Because then we should rather just do the same nil check as a few lines below and also return nil instead of answering the request with 403.

At least this Lua function does not seem to be the right place for generating the final response to me.

Exactly, for the reasons you mentioned. I will add tests, but I'm not very familiar with this, so it will take me some time.

ZJfans · 2024-08-30T13:43:41Z

@Gacko
I have a question, e2e does not allow post, but I need to test get and post, can you give me some advice

f.HTTPTestClient().
		    POST("/").
		    WithHeader("Host", host).
		    Expect().
		    Status(http.StatusForbidden)

run golangci-lint
  Running [/home/runner/golangci-lint-1.56.2-linux-amd64/golangci-lint run] in [/home/runner/work/ingress-nginx/ingress-nginx] ...
  test/e2e/annotations/affinity.go:1: : # k8s.io/ingress-nginx/test/e2e/annotations
  Error: test/e2e/annotations/limitexcept.go:60:7: f.HTTPTestClient().POST undefined (type *httpexpect.HTTPRequest has no field or method POST)
  Error: test/e2e/annotations/limitexcept.go:72:7: f.HTTPTestClient().POST undefined (type *httpexpect.HTTPRequest has no field or method POST) (typecheck)
  /*
  Error: test/e2e/e2e.go:[33](https://github.com/kubernetes/ingress-nginx/actions/runs/10597984395/job/29369438735?pr=11860#step:5:35):4: could not import k8s.io/ingress-nginx/test/e2e/annotations (-: # k8s.io/ingress-nginx/test/e2e/annotations
  Error: test/e2e/annotations/limitexcept.go:60:7: f.HTTPTestClient().POST undefined (type *httpexpect.HTTPRequest has no field or method POST)
  Error: test/e2e/annotations/limitexcept.go:72:7: f.HTTPTestClient().POST undefined (type *httpexpect.HTTPRequest has no field or method POST)) (typecheck)
  	_ "k8s.io/ingress-nginx/test/e2e/annotations"
  	  ^
  
  Error: issues found
  Ran golangci-lint in 86874ms

Gacko · 2024-08-31T07:48:31Z

We had a chat about this PR in our Community Meeting and came to the conclusion that this is not the ideal place to add this kind of error handling.

The function you're adding it to is meant for determining the upstream to use and not for making a final decision about the HTTP status code, especially not a 403.

I cannot tell if there is a more proper way to handle this as, from the top of my head, I don't know if this issue is more about the order NGINX is executing Lua and/or plain directives in the nginx.conf or could maybe solved by just not returning a 503 here, or at least not if the backend name is undefined / set to - from the very beginning.

Gacko · 2024-08-31T07:48:46Z

/cc @strongjz WDYT?

ZJfans · 2024-08-31T11:11:51Z

It's great that you discussed this issue. I also think this fix is not good enough. But I can't think of a better solution. The good thing is that this error has a small impact, just the expected 403 becomes 503.

I think the order is, 1. If a request is forbidden, nginx updates the configuration of the location block to the limit_except block (excluding the location configuration) 2. Lua gets the variable set in the location block (error occurs) 3. Execute the limit_except logic.

I think it's better to merge the location block configuration instead of simply replacing it. Maybe nginx thinks that the request is forbidden and should not get the original location block configuration again, because it will return 403 anyway.

Maybe my analysis is wrong, this is interesting, and I look forward to a good solution. And more importantly, limit_except should be used with caution in the future to prevent interference with other location directives.

github-actions · 2024-10-16T02:04:08Z

This is stale, but we won't close it automatically, just bare in mind the maintainers may be busy with other tasks and will reach your issue ASAP. If you have any question or request to prioritize this, please reach #ingress-nginx-dev on Kubernetes Slack.

k8s-triage-robot · 2024-10-16T04:59:51Z

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…11742)

k8s-ci-robot requested a review from puerco August 24, 2024 18:33

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ZJfans marked this pull request as draft August 25, 2024 05:37

k8s-ci-robot added the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Aug 25, 2024

ZJfans marked this pull request as ready for review August 25, 2024 05:56

k8s-ci-robot removed the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Aug 25, 2024

k8s-ci-robot requested review from Gacko and strongjz August 25, 2024 05:56

Gacko changed the title ~~fix: limit_except returns 503 instead of the correct 403 (#11742)~~ Lua: Check backend name to be non-nil. Aug 26, 2024

k8s-ci-robot added the do-not-merge/hold Indicates that a PR should not merge because someone has issued a /hold command. label Aug 26, 2024

k8s-ci-robot added ok-to-test Indicates a non-member PR verified by an org member that is safe to test. and removed needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels Aug 26, 2024

Gacko changed the title ~~Lua: Check backend name to be non-nil.~~ Lua: Fix limit_except returning 503. Aug 26, 2024

Gacko requested changes Aug 26, 2024

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k8s-ci-robot added size/M Denotes a PR that changes 30-99 lines, ignoring generated files. and removed size/XS Denotes a PR that changes 0-9 lines, ignoring generated files. labels Aug 28, 2024

ZJfans force-pushed the fix_limit_except_503 branch from 952020f to 35657b3 Compare August 28, 2024 13:45

github-actions bot added the lifecycle/frozen Indicates that an issue or PR should not be auto-closed due to staleness. label Oct 16, 2024

k8s-ci-robot removed the lifecycle/frozen Indicates that an issue or PR should not be auto-closed due to staleness. label Oct 16, 2024

ZJfans added 2 commits November 13, 2024 15:25

fix: limit_except returns 503 instead of the correct 403 (kubernetes#…

72ff20f

…11742)

Add tests for limit_except

8104914

strongjz force-pushed the fix_limit_except_503 branch from 35657b3 to 8104914 Compare November 13, 2024 22:25

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Lua: Fix `limit_except` returning 503. #11860

Lua: Fix `limit_except` returning 503. #11860

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Lua: Fix limit_except returning 503. #11860

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Lua: Fix limit_except returning 503. #11860

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Lua: Fix `limit_except` returning 503. #11860

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