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898695e312
This allows gitops-pusher to detect external ACL changes. I'm not sure what to call this problem, so I've been calling it the "three version problem" in my notes. The basic problem is that at any given time we only have two versions of the ACL file at any given point: the version in CONTROL and the one in the git repo. In order to check if there has been tampering of the ACL files in the admin panel, we need to have a _third_ version to compare against. In this case I am not storing the old ACL entirely (though that could be a reasonable thing to add in the future), but only its sha256sum. This allows us to detect if the shasum in control matches the shasum we expect, and if that expectation fails, then we can react accordingly. This will require additional configuration in CI, but I'm sure that can be done. Signed-off-by: Xe <xe@tailscale.com>
68 lines
2.0 KiB
Go
68 lines
2.0 KiB
Go
// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"encoding/json"
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"os"
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)
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// Cache contains cached information about the last time this tool was run.
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//
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// This is serialized to a JSON file that should NOT be checked into git.
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// It should be managed with either CI cache tools or stored locally somehow. The
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// exact mechanism is irrelevant as long as it is consistent.
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//
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// This allows gitops-pusher to detect external ACL changes. I'm not sure what to
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// call this problem, so I've been calling it the "three version problem" in my
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// notes. The basic problem is that at any given time we only have two versions
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// of the ACL file at any given point. In order to check if there has been
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// tampering of the ACL files in the admin panel, we need to have a _third_ version
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// to compare against.
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//
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// In this case I am not storing the old ACL entirely (though that could be a
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// reasonable thing to add in the future), but only its sha256sum. This allows
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// us to detect if the shasum in control matches the shasum we expect, and if that
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// expectation fails, then we can react accordingly.
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type Cache struct {
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PrevETag string // Stores the previous ETag of the ACL to allow
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}
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// Save persists the cache to a given file.
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func (c *Cache) Save(fname string) error {
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os.Remove(fname)
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fout, err := os.Create(fname)
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if err != nil {
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return err
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}
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defer fout.Close()
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return json.NewEncoder(fout).Encode(c)
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}
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// LoadCache loads the cache from a given file.
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func LoadCache(fname string) (*Cache, error) {
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var result Cache
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fin, err := os.Open(fname)
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if err != nil {
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return nil, err
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}
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defer fin.Close()
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err = json.NewDecoder(fin).Decode(&result)
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if err != nil {
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return nil, err
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}
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return &result, nil
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}
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// Shuck removes the first and last character of a string, analogous to
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// shucking off the husk of an ear of corn.
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func Shuck(s string) string {
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return s[1 : len(s)-1]
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}
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