Add an example fuzzing test

README.md

@@ -61,6 +61,41 @@ To keep track of upstream AMCL:
 - Test
 - Commit
 
+### Executing the test suite
+
+We recomment working within the nimbus build environment described here:
+https://github.com/status-im/nim-beacon-chain/
+
+To execute the test suite, just navigate to the root of this repo and execute:
+
+```
+nimble test
+```
+
+> Please note that within the nimbus build environment, the repository will
+  be located in `nim-beacon-chain/vendor/nim-blscurve`.
+
+### Executing the fuzzing tests
+
+Before you start, please make sure that the regular test suite executes
+successfully (see the instructions above). To start a particular fuzzing
+test, navigate to the root of this repo and execute:
+
+```
+nim tests/fuzzing/run_fuzzing_test.nims <test-name>
+```
+
+You can specify the fuzzing engine being used by passing an additional
+`--fuzzer` parameter. The currently supported engines are `libFuzzer`
+(used by default) and `afl`.
+
+All fuzzing tests are located in `tests/fuzzing` and use the following
+naming convention:
+
+```
+fuzz_<test-name>.nim
+```
+
 ## License
 
 Licensed and distributed under either of

tests/eth2_vectors.nim

@@ -12,28 +12,19 @@
 
 import
   # Standard library
-  json, strutils, os, streams, unittest,
-  # Third party
-  yaml,
+  json, strutils, os, unittest,
   # Status libraries
   stew/byteutils,
   # Public API
-  ../blscurve
+  ../blscurve,
+  # Test helpers
+  ./test_locator
 
-const ETH2_DIR = currentSourcePath.rsplit(DirSep, 1)[0] / "eth2.0_v0.10.1_vectors"
+type InOut = enum
+  Input
+  Output
 
-proc parseTest(file: string): JsonNode =
-  var yamlStream = openFileStream(file)
-  defer: yamlStream.close()
-  result = yamlStream.loadToJson()[0]
-
-const SkippedTests = [
-  "small"/"fast_aggregate_verify_e6922a0d196d9869"/"data.yaml", # Buggy upstream vector: https://github.com/ethereum/eth2.0-specs/issues/1618
-  "small"/"fast_aggregate_verify_62bca7cd61880e26"/"data.yaml",
-  "small"/"fast_aggregate_verify_3b2b0141e95125f0"/"data.yaml",
-]
-
-template testGen(name, testJson, body: untyped): untyped =
+template testGen*(name, testJson, body: untyped): untyped =
   ## Generates a test proc
   ## with identifier "test_name"
   ## The test file is availaible as JsonNode under the
@@ -41,14 +32,9 @@ template testGen(name, testJson, body: untyped): untyped =
   proc `test _ name`() =
     var count = 0 # Need to fail if walkDir doesn't return anything
     var skipped = 0
-    const testDir = ETH2_DIR / astToStr(name)
-    for file in walkDirRec(testDir, relative = true):
-      if file in SkippedTests:
-        echo "[WARNING] Skipping - ", file
-        inc skipped
-        continue
+    for dir, file in walkTests(astToStr(name), skipped):
       echo "       ", astToStr(name), " test: ", file
-      let testJson = parseTest(testDir / file)
+      let testJson = parseTest(dir / file)
 
       body
 
@@ -58,10 +44,6 @@ template testGen(name, testJson, body: untyped): untyped =
     if skipped > 0:
       echo "[Warning]: ", skipped, " tests skipped."
 
-type InOut = enum
-  Input
-  Output
-
 proc getFrom(T: typedesc, test: JsonNode, inout: static InOut): T =
   when inout == Output:
     when T is bool:

tests/fuzzing/collect_corpus.nim

@@ -0,0 +1,34 @@
+import
+  stew/byteutils,
+  ../test_locator,
+  fuzzing_assumptions
+
+var skipped = 0
+
+let corpusDir = getAppDir() / "corpus"
+
+removeDir corpusDir
+
+template getInputBytes(test: JsonNode, fieldName: string): seq[byte] =
+  test["input"][fieldName].getStr.hexToSeqByte
+
+var inputIdx = 0
+template nextInput: string =
+  inc inputIdx
+  "input" & $inputIdx
+
+let verifyCorpusDir = corpusDir / "verify"
+createDir verifyCorpusDir
+
+for dir, test in walkTests("verify", skipped):
+  let t = parseTest(dir / test)
+  let
+    message = t.getInputBytes "message"
+    pubKey = t.getInputBytes "pubkey"
+    signature = t.getInputBytes "signature"
+
+  doAssert pubKey.len == fuzzing_assumptions.pubkeyLen and
+           signature.len == fuzzing_assumptions.signatureLen
+
+  writeFile(verifyCorpusDir / nextInput(), message & pubkey & signature)
+

tests/fuzzing/fuzz_verify.nim

@@ -0,0 +1,23 @@
+import
+  testutils/fuzzing, stew/byteutils,
+  ../../blscurve, fuzzing_assumptions
+
+test:
+  block:
+    if payload.len < pubkeyLen + signatureLen:
+      break
+
+    let
+      signatureStart = payload.len - signatureLen
+      pubkeyStart = signatureStart - pubkeyLen
+
+    var sig: Signature
+    if not sig.fromBytes(payload[signatureStart ..< (signatureStart + signatureLen)]):
+      break
+
+    var pubKey: PublicKey
+    if not pubKey.fromBytes(payload[pubkeyStart ..< (pubkeyStart + pubkeyLen)]):
+      break
+
+    discard pubKey.verify(payload[0 ..< pubkeyStart], sig)
+

tests/fuzzing/fuzzing_assumptions.nim

@@ -0,0 +1,4 @@
+const
+  pubkeyLen* = 48
+  signatureLen* = 96
+

tests/fuzzing/run_fuzzing_test.nims

@@ -0,0 +1,22 @@
+import strformat
+import os except paramCount, paramStr, fileExists # these are also defined in the system module
+import confutils, testutils/fuzzing_engines
+
+cli do (testName {.argument.}: string,
+        fuzzer = libFuzzer):
+  let
+    fuzzingDir = thisDir()
+    fuzzingFile = fuzzingDir / "fuzz_" & addFileExt(testName, "nim")
+    corpusDir = fuzzingDir / "corpus" / testName
+
+  if not fileExists(fuzzingFile):
+    echo testName, " is not a recognized fuzzing test"
+    quit 1
+
+  let
+    collectCorpusNim = fuzzingDir / "collect_corpus.nim"
+    fuzzNims = fuzzingDir / ".." / ".." / ".." / "nim-testutils" / "testutils" / "fuzzing" / "fuzz.nims"
+
+  exec &"""nim c -r "{collectCorpusNim}""""
+  exec &"""nim "{fuzzNims}" {fuzzer} "{fuzzingFile}" "{corpusDir}" """
+

tests/test_locator.nim

@@ -0,0 +1,33 @@
+import
+  # Standard library
+  json, strutils, os, streams,
+  # Third party
+  yaml
+
+export
+  os, json
+
+const ETH2_DIR = currentSourcePath.rsplit(DirSep, 1)[0] / "eth2.0_v0.10.1_vectors"
+
+proc parseTest*(file: string): JsonNode =
+  var yamlStream = openFileStream(file)
+  defer: yamlStream.close()
+  result = yamlStream.loadToJson()[0]
+
+const SkippedTests = [
+  "small"/"fast_aggregate_verify_e6922a0d196d9869"/"data.yaml", # Buggy upstream vector: https://github.com/ethereum/eth2.0-specs/issues/1618
+  "small"/"fast_aggregate_verify_62bca7cd61880e26"/"data.yaml",
+  "small"/"fast_aggregate_verify_3b2b0141e95125f0"/"data.yaml",
+]
+
+iterator walkTests*(category: string, skipped: var int): (string, string) =
+  let testDir = ETH2_DIR / category
+
+  for file in walkDirRec(testDir, relative = true):
+    if file in SkippedTests:
+      echo "[WARNING] Skipping - ", file
+      inc skipped
+      continue
+
+    yield (testDir, file)
+