hcl/json: fuzzing utilities

hcl/json/fuzz/.gitignore

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+fuzz*-fuzz.zip

hcl/json/fuzz/Makefile

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+
+ifndef FUZZ_WORK_DIR
+$(error FUZZ_WORK_DIR is not set)
+endif
+
+default:
+	@echo "See README.md for usage instructions"
+
+fuzz-config: fuzz-exec-config
+
+fuzz-exec-%: fuzz%-fuzz.zip
+	go-fuzz -bin=./fuzz$*-fuzz.zip -workdir=$(FUZZ_WORK_DIR)
+
+fuzz%-fuzz.zip: %/fuzz.go
+	go-fuzz-build github.com/hashicorp/hcl2/hcl/json/fuzz/$*
+
+tools:
+	go get -u github.com/dvyukov/go-fuzz/go-fuzz
+	go get -u github.com/dvyukov/go-fuzz/go-fuzz-build
+
+clean:
+	rm fuzz*-fuzz.zip
+
+.PHONY: tools clean fuzz-config fuzz-expr fuzz-template fuzz-traversal
+.PRECIOUS: fuzzconfig-fuzz.zip fuzzexpr-fuzz.zip fuzztemplate-fuzz.zip fuzztraversal-fuzz.zip

hcl/json/fuzz/README.md

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+# JSON syntax fuzzing utilities
+
+This directory contains helper functions and corpuses that can be used to
+fuzz-test the HCL JSON parser using [go-fuzz](https://github.com/dvyukov/go-fuzz).
+
+To fuzz, first install go-fuzz and its build tool in your `GOPATH`:
+
+```
+$ make tools
+```
+
+Now you can fuzz one or all of the parsers:
+
+```
+$ make fuzz-config FUZZ_WORK_DIR=/tmp/hcl2-fuzz-config
+```
+
+In all cases, set `FUZZ_WORK_DIR` to a directory where `go-fuzz` can keep state
+as it works. This should ideally be in a ramdisk for efficiency, and should
+probably _not_ be on an SSD to avoid thrashing it.
+
+## Understanding the result
+
+A small number of subdirectories will be created in the work directory.
+
+If you let `go-fuzz` run for a few minutes (the more minutes the better) it
+may detect "crashers", which are inputs that caused the parser to panic. Details
+about these are written to `$FUZZ_WORK_DIR/crashers`:
+
+```
+$ ls /tmp/hcl2-fuzz-config/crashers
+7f5e9ec80c89da14b8b0b238ec88969f658f5a2d
+7f5e9ec80c89da14b8b0b238ec88969f658f5a2d.output
+7f5e9ec80c89da14b8b0b238ec88969f658f5a2d.quoted
+```
+
+The base file above (with no extension) is the input that caused a crash. The
+`.output` file contains the panic stack trace, which you can use as a clue to
+figure out what caused the crash.
+
+A good first step to fixing a detected crasher is to copy the failing input
+into one of the unit tests in the `hcl/json` package and see it crash there
+too. After that, it's easy to re-run the test as you try to fix it. The
+file with the `.quoted` extension contains a form of the input that is quoted
+in Go syntax for easy copy-paste into a test case, even if the input contains
+non-printable characters or other inconvenient symbols.
+
+## Rebuilding for new Upstream Code
+
+An archive file is created for `go-fuzz` to use on the first run of each
+of the above, as a `.zip` file created in this directory. If upstream code
+is changed these will need to be deleted to cause them to be rebuilt with
+the latest code:
+
+```
+$ make clean
+```

hcl/json/fuzz/config/corpus/attr-expr.hcl.json

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+{
+    "foo": "${upper(bar + baz[1])}"
+}

hcl/json/fuzz/config/corpus/attr-literal.hcl.json

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+{
+    "foo": "bar"
+}

hcl/json/fuzz/config/corpus/block-attrs.hcl.json

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+{
+  "block": {
+    "foo": true
+  }
+}

hcl/json/fuzz/config/corpus/block-empty.json

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+{
+    "block": {}
+}

hcl/json/fuzz/config/corpus/block-nested.hcl.json

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+{
+  "block": {
+    "another_block": {
+      "foo": "bar"
+    }
+  }
+}

hcl/json/fuzz/config/corpus/empty.hcl.json

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+{}

hcl/json/fuzz/config/corpus/list-empty.json

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+{
+    "hello": []
+}

hcl/json/fuzz/config/corpus/list-nested.json

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+{
+    "hello": [[]]
+}

hcl/json/fuzz/config/corpus/list-values.json

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+{
+    "hello": [
+        "hello",
+        true,
+        1.2
+    ]
+}

hcl/json/fuzz/config/corpus/number-big.hcl.json

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+{
+    "foo": 1.234234e30
+}

hcl/json/fuzz/config/corpus/number-int.hcl.json

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+{
+    "foo": 1024
+}

hcl/json/fuzz/config/corpus/utf8.hcl.json

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+{
+    "foo": "föo ${föo(\"föo\")}"
+}

hcl/json/fuzz/config/fuzz.go

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+package fuzzconfig
+
+import (
+	"github.com/hashicorp/hcl2/hcl/json"
+)
+
+func Fuzz(data []byte) int {
+	_, diags := json.Parse(data, "<fuzz-conf>")
+
+	if diags.HasErrors() {
+		return 0
+	}
+
+	return 1
+}