LSM sensor

[anfedotoff]

LSM sensor support allows to use LSM BPF programs the way we use BPF programs for kprobes/tracepoints/uprobes.

TracingPolicy example:

apiVersion: cilium.io/v1alpha1
kind: TracingPolicy
metadata:
  name: "lsm"
spec:
  lsmhooks:
  - hook: "file_open"
    args:
      - index: 0
        type: "file"
    selectors:
    - matchBinaries:
      - operator: "In"
        values:
        - "/usr/bin/cat"

Event example:

{                                                                                                     
  "process_lsm": {                                                                                    
    "process": {                                                                                      
      "exec_id": "dXNlci1uaXg6MTk5MzE1NDk0NTk3MzM6MzIwMTA4",                                  
      "pid": 320108,                                                                                  
      "uid": 1000,                                                                                    
      "cwd": "/home/user/go/src/github.com/cilium/tetragon",                                    
      "binary": "/usr/bin/cat",                                                                       
      "arguments": "/etc/passwd",                                                                     
      "flags": "execve clone",                                                                        
      "start_time": "2024-06-15T18:03:29.742161520Z",                                                                                                                                                       
      "auid": 1000,                                                                                   
      "parent_exec_id": "dXNlci1uaXg6ODg1NjMwMDAwMDAwMDoxNDc4MTI=",                                                                                                                                 
      "refcnt": 1,                                                                                    
      "tid": 320108,                                                                                  
      "user": {                                                                                       
        "name": "user"                                                                          
      }                                                                                               
    },                                                                                                
    "parent": {                                                                                       
      "exec_id": "dXNlci1uaXg6ODg1NjMwMDAwMDAwMDoxNDc4MTI=",                                  
      "pid": 147812,                                                                                  
      "uid": 1000,                                                                                    
      "cwd": "/home/user/go/src/github.com/cilium/tetragon",                                                                                                                                          
      "binary": "/usr/bin/zsh",                                                                                                                                                                             
      "flags": "procFS auid",                                                                         
      "start_time": "2024-06-15T14:37:33.597296165Z",
      "auid": 1000,
      "parent_exec_id": "dXNlci1uaXg6MTM1ODA0MDAwMDAwMDozMTQ2",
      "tid": 147812
    },
    "function_name": "file_open",
    "policy_name": "lsm",
    "args": [
      {
        "file_arg": {
          "path":"/etc/passwd",
          "permission":"-rw-r--r--"
        }
      }
    ],
    "action": "KPROBE_ACTION_POST"
  },
  "node_name": "user-nix",
  "time": "2024-06-15T18:03:29.743030933Z"
}

This is also necessary for #2409.

[netlify]

✅ Deploy Preview for tetragon ready!

Name	Link
🔨 Latest commit	e0f9144
🔍 Latest deploy log	https://app.netlify.com/sites/tetragon/deploys/6686edcd56030e00097020d9
😎 Deploy Preview	https://deploy-preview-2566--tetragon.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[anfedotoff]

There are things to do:

• Fix tests
• Add lsm test
• Decide minimal kernel version for LSM sensor support (LSM BPF is needed 5.7 kernel).
• Fix some bugs in code and make it more neat.

I managed to load LSM BPF programs, tail calls also work for LSM programs! The most terrifying problems are solved, I think. I managed to catch some Lsm events).

[anfedotoff]

For now I managed to fix problem with args resolving. LSM BPF programs get args the way raw tracepoint programs do. So, LSM events now are looking good. It would be nice to start code review.

Some open questions:

• ./verify/verify.sh . I made a hack for loading generic LSM programs. But I need to install llvm-objcopy in CI
• Tests. I think we need some tests. Maybe more than one. I'll work on it. Maybe we discuss what kind of tests it's good to have?
• Enforce mode. If LSM BPF returns the value that is not qual to zero, than operation is not permitted. Maybe we should add an action for that? For example, if policy is violated just return -EPERM, instead of sending SIGKILL.

@kkourt, @olsajiri, @mtardy please could you have a look?

[kkourt]

Thanks!

Overall, this looks good to me! I've left some minor comments.

./verify/verify.sh . I made a hack for loading generic LSM programs. But I need to install llvm-objcopy in CI

Looks good to me. Yap, let's install it. I'm guessing it should be part of our clang container so we can just use that.

Tests. I think we need some tests. Maybe more than one. I'll work on it. Maybe we discuss what kind of tests it's good to have?

That's a good question. I would say start simple, and have one or two tests for the basic functionality (observability and enforcement)

Enforce mode. If LSM BPF returns the value that is not qual to zero, than operation > is not permitted. Maybe we should add an action for that? For example, if policy is > violated just return -EPERM, instead of sending SIGKILL.

Yap, I think that makes sense. We also have an override action that does something similar, but having a separate action for lsm (as you do in your PR) makes sense to me.

[kkourt]

It would have been nice to use the new interface, but it's not clear when it's going to be ready: #2128.

CC: @olsajiri

[kkourt]

@olsajiri I added you to the reviewers. It would be great if you could have a look when you get a chance. Thanks!