[golang] Added 2 fuzzers (#5437)

* [golang] Added 2 fuzzers

* Change fuzzer to call exported targets

* Added fuzzer

projects/golang/Dockerfile

@@ -17,6 +17,6 @@
 FROM gcr.io/oss-fuzz-base/base-builder
 
 RUN git clone --depth 1 https://github.com/dvyukov/go-fuzz-corpus golang
-COPY build.sh $SRC/
+COPY build.sh math_big_fuzzer.go $SRC/
 
 WORKDIR $SRC/golang

projects/golang/build.sh

@@ -15,8 +15,14 @@
 # These two dependencies cause build issues and are not used by oss-fuzz:
 rm -r sqlparser
 rm -r parser
+
+mkdir math && cp $SRC/math_big_fuzzer.go ./math/
+
 go mod init "github.com/dvyukov/go-fuzz-corpus"
 export FUZZ_ROOT="github.com/dvyukov/go-fuzz-corpus"
+compile_go_fuzzer $FUZZ_ROOT/math FuzzBigIntCmp1 big_cmp_fuzzer1
+compile_go_fuzzer $FUZZ_ROOT/math FuzzBigIntCmp2 big_cmp_fuzzer2
+compile_go_fuzzer $FUZZ_ROOT/math FuzzRatSetString big_rat_fuzzer
 compile_go_fuzzer $FUZZ_ROOT/asn1 Fuzz asn_fuzzer
 compile_go_fuzzer $FUZZ_ROOT/csv Fuzz csv_fuzzer
 compile_go_fuzzer $FUZZ_ROOT/elliptic Fuzz elliptic_fuzzer

projects/golang/math_big_fuzzer.go

@@ -0,0 +1,63 @@
+// Copyright 2021 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.
+//
+
+
+package mathfuzzer
+
+import "math/big"
+
+func FuzzBigIntCmp1(data []byte) int {
+    if !isDivisibleBy(len(data), 2) {
+        return -1
+    }
+    i1 := new(big.Int)
+    i2 := new(big.Int)
+
+    half := len(data) / 2
+
+    halfOne := data[:half]
+    halfTwo := data[half:]
+
+    i1.SetBytes(halfOne)
+    i2.SetBytes(halfTwo)
+
+    i1.Cmp(i2)
+    return 1
+}
+
+func FuzzBigIntCmp2(data []byte) int {
+    if !isDivisibleBy(len(data), 2) {
+        return -1
+    }
+    x, y := new(big.Int), new(big.Int)
+    half := len(data)/2
+    if err := x.UnmarshalText(data[:half]); err != nil {
+      return 0
+    }
+    if err := y.UnmarshalText(data[half:]); err != nil {
+      return 0
+    }
+    x.Cmp(y)
+    return 1
+}
+
+func FuzzRatSetString(data []byte) int {
+    _, _ = new(big.Rat).SetString(string(data))
+    return 1
+}
+
+func isDivisibleBy(n int, divisibleby int) bool {
+    return (n % divisibleby) == 0
+}