Allow for fuzzing with libFuzzer

tests/fuzzing/discovery/fuzz.nim

@@ -1,55 +1,25 @@
 import
-  streams, posix, sequtils, strutils, chronicles, chronos, stew/byteutils,
-  eth/p2p/[discovery, kademlia, enode], eth/[keys, rlp],
-  ../../p2p/p2p_test_helper
-
-template fuzz(body) =
-  # For code we want to fuzz.
-  try:
-    body
-  except:
-    let e = getCurrentException()
-    debug "Fuzzer input created exception", exception=e.name, trace=e.repr
-    discard kill(getpid(), SIGSEGV)
-
-template noFuzz(body) =
-  # For code not in the scope of the test.
-  # Lets not have false negatives due to possible issues in this code.
-  try:
-    body
-  except:
-    let e = getCurrentException()
-    debug "Exception out of scope of the fuzzing target",
-      exception=e.name, trace=e.repr
-    return
+  chronicles, eth/p2p/[discovery, enode], eth/[keys, rlp],
+  ../../p2p/p2p_test_helper, ../fuzz_helpers
 
 const DefaultListeningPort = 30303
+var targetNode: DiscoveryProtocol
 
-proc fuzzTest() =
+proc init() =
+  # Set up a discovery node, this is the node we target when fuzzing
   var
-    msg: seq[byte]
-    address: Address
-    targetNode: DiscoveryProtocol
-
-  noFuzz:
-    # Set up a discovery node, this is the node we target with fuzzing
-    let
     targetNodeKey = initPrivateKey("a2b50376a79b1a8c8a3296485572bdfbf54708bb46d3c25d73d2723aaaf6a617")
     targetNodeAddr = localAddress(DefaultListeningPort)
   targetNode = newDiscoveryProtocol(targetNodeKey, targetNodeAddr, @[])
   # Create the transport as else replies on the messages send will fail.
   targetNode.open()
 
-    # Read input from stdin (fastest for AFL)
-    let s = newFileStream(stdin)
-    # We use binary files as with hex we can get lots of "not hex" failures
-    var input = s.readAll()
-    s.close()
-    # Remove newline if it is there
-    input.removeSuffix
-    # TODO: is there a better/faster way?
-    let payload = input.mapIt(it.byte)
+proc test(payload: seq[byte]) =
+  var
+    msg: seq[byte]
+    address: Address
 
+  fuzz:
     # Sending raw payload is possible but won't find us much. We need a hash and
     # a signature, and without it there is a big chance it will always result in
     # "Wrong msg mac from" error.
@@ -64,5 +34,31 @@ proc fuzzTest() =
     except RlpError, DiscProtocolError:
       debug "Receive failed", err = getCurrentExceptionMsg()
 
-fuzz:
-  fuzzTest()
+proc NimMain() {.importc: "NimMain".}
+
+proc fuzzerInit(): cint {.exportc: "LLVMFuzzerInitialize".} =
+  NimMain()
+
+  init()
+
+  return 0
+
+template `+`*[T](p: ptr T, off: int): ptr T =
+  cast[ptr type(p[])](cast[ByteAddress](p) +% off * sizeof(p[]))
+
+proc fuzzerCall(data: ptr byte, len: csize): cint {.exportc: "LLVMFuzzerTestOneInput".} =
+  if len > 0:
+    var input: seq[byte]
+
+    # TODO: something better to get this data in the seq?
+    newSeq(input, len)
+    for i in 0..<len:
+      input[i] = (data + i)[]
+
+    test(input)
+
+  return 0
+
+when defined(afl):
+  init()
+  test(readStdin())

tests/fuzzing/fuzz.nims

@@ -7,8 +7,7 @@ if not dirExists("generated-input"):
 if not fileExists("fuzz"):
   # Requires afl-gcc to be installed
   # TODO: add + test option for clang
-  exec "nim c --cc=gcc --gcc.exe=afl-gcc --gcc.linkerexe=afl-gcc fuzz"
-
+  exec "nim c -d:afl -d:noSignalHandler --cc=gcc --gcc.exe=afl-gcc --gcc.linkerexe=afl-gcc fuzz"
 if dirExists("output"):
   exec "afl-fuzz -i - -o output -M fuzzer01 -- ./fuzz"
 else:

tests/fuzzing/fuzz_helpers.nim

@@ -0,0 +1,27 @@
+import streams, posix, sequtils, strutils, chronicles
+
+template fuzz*(body) =
+  # For code we want to fuzz, SIGSEGV is needed on unwanted exceptions.
+  # However, this is only needed when fuzzing with afl.
+  when defined(afl):
+    try:
+      body
+    except Exception as e:
+      error "Fuzzer input created exception", exception=e.name, trace=e.repr, msg=e.msg
+      discard kill(getpid(), SIGSEGV)
+  else:
+    body
+
+proc readStdin*(): seq[byte] =
+  # Read input from stdin (fastest for AFL)
+  let s = newFileStream(stdin)
+  if s.isNil:
+    error "Error opening stdin"
+    discard kill(getpid(), SIGSEGV)
+  # We use binary files as with hex we can get lots of "not hex" failures
+  var input = s.readAll()
+  s.close()
+  # Remove newline if it is there
+  input.removeSuffix
+  # TODO: is there a better/faster way?
+  result = input.mapIt(it.byte)