[opus] Add new fuzzer (#4118)

* added new opus fuzzer, build working

* added missing license header, cleaned up Dockerfile

* fixed build process

* changed build process depending on C or C++ fuzzer

* converted opus_multi_fuzzer from C++ to C, reverted build script to only accept C files

3 files changed, 103 insertions, 2 deletions

diff --git a/projects/opus/Dockerfile b/projects/opus/Dockerfile
index ccdd01937..717b88270 100644
--- a/projects/opus/Dockerfile
+++ b/projects/opus/Dockerfile
@@ -21,3 +21,4 @@ RUN git clone https://gitlab.xiph.org/xiph/opus.git
 RUN wget https://opus-codec.org/static/testvectors/opus_testvectors.tar.gz
 WORKDIR opus
 COPY build.sh $SRC/
+COPY *.c tests/
diff --git a/projects/opus/build.sh b/projects/opus/build.sh
index 0cd91bf76..850007151 100644
--- a/projects/opus/build.sh
+++ b/projects/opus/build.sh
@@ -16,7 +16,7 @@
 ##############################################################################
 set -eu
 
-FUZZERS="opus_decode_fuzzer"
+FUZZERS="opus_decode_fuzzer opus_multi_fuzzer"
 BUILDS=(floating fixed)
 
 tar xvf $SRC/opus_testvectors.tar.gz
@@ -53,7 +53,8 @@ for build in "${BUILDS[@]}"; do
 
     # Setup the .options and test corpus zip files using the corresponding
     # fuzzer's name
-    cp tests/$fuzzer.options $OUT/${fuzzer}_${build}.options
+    [ -f tests/$fuzzer.options ] \
+        && cp tests/$fuzzer.options $OUT/${fuzzer}_${build}.options
     zip -r $OUT/${fuzzer}_${build}_seed_corpus.zip opus_testvectors/
   done
 done
diff --git a/projects/opus/opus_multi_fuzzer.c b/projects/opus/opus_multi_fuzzer.c
new file mode 100644
index 000000000..de63bfb3e
--- /dev/null
+++ b/projects/opus/opus_multi_fuzzer.c
@@ -0,0 +1,99 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <stddef.h>
+#include <stdlib.h>
+
+#include "opus.h"
+#include "opus_multistream.h"
+
+struct TocInfo {
+  opus_int32 frequency;  // in [Hz*1000]
+  int channels;          // number of channels; either 1 or 2
+  int frame_len_x2;      // in [ms*2]. x2 is to avoid float value of 2.5 ms
+};
+
+void extractTocInfo(const uint8_t toc, struct TocInfo *const info) {
+  const int frame_lengths_x2[3][4] = {
+    {20, 40, 80, 120},
+    {20, 40, 20, 40},
+    {5, 10, 20, 40}
+  };
+
+  info->channels = toc & 4 ? 2 : 1;
+
+  const uint8_t config = toc >> 3;
+
+  int len_index;
+  if (config < 12) {
+    len_index = 0;
+  } else if (config < 16) {
+    len_index = 1;
+  } else {
+    len_index = 2;
+  }
+  info->frame_len_x2 = frame_lengths_x2[len_index][config & 3];
+
+  switch (config >> 2) {
+    case 0: info->frequency = 8; break;
+    case 1: info->frequency = 12; break;
+    case 2: info->frequency = 16; break;
+    case 3: info->frequency = (config < 14) ? 24 : 48; break;
+    case 4: info->frequency = 8; break;
+    case 5: info->frequency = 16; break;
+    case 6: info->frequency = 24; break;
+    default: info->frequency = 48; break;
+  }
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  if (size < 3 || size > 1000000) return 0;
+
+  // Using last byte as a number of streams (instead of rand_r). Each stream
+  // should be at least 3 bytes long hence divmod.
+  int streams = 1 + data[size - 1] % (size / 3);
+  if (streams > 255) streams = 255;
+  unsigned char *mapping = (unsigned char*) malloc(sizeof(unsigned char)*streams);
+  if (!mapping) return 0;
+
+  for (int i = 0; i < streams; ++i) {
+    mapping[i] = i;
+  }
+
+  struct TocInfo info;
+  extractTocInfo(*data, &info);
+
+  int error = 0;
+  OpusMSDecoder *const decoder = opus_multistream_decoder_create(
+      info.frequency * 1000, streams, streams, 0, mapping, &error);
+
+  if (!decoder || error) return 0;
+
+  const int frame_size = (info.frequency * info.frame_len_x2) / 2;
+  opus_int16 *pcm = (opus_int16*) malloc(sizeof(opus_int16)*frame_size*streams);
+  if (!pcm) goto exit;
+
+  // opus_decode wants us to use its return value, but we don't really care.
+  const int foo =
+      opus_multistream_decode(decoder, data, size, pcm, frame_size, 0);
+  (void)foo;
+
+  opus_multistream_decoder_destroy(decoder);
+
+  free(pcm);
+
+exit:
+  free(mapping);
+  return 0;
+}