prog: use separate allocation size for KFuzzTest arguments

Author: Ethan Graham

prog/kfuzztest.go

@@ -22,6 +22,9 @@ const (
 	// x86_64, so we hardcode it for now. A more robust solution would involve
 	// reading this from the debugfs entry at boot before fuzzing begins.
 	kFuzzTestMinalign uint64 = 8
+
+	// Maximum input size accepted by the KFuzzTest kernel module.
+	KFuzzTestMaxInputSize uint64 = 64 << 10
 )
 
 func kFuzzTestWritePrefix(buf *bytes.Buffer) {

prog/rand.go

@@ -368,6 +368,10 @@ func (r *randGen) randString(s *state, t *BufferType) []byte {
 }
 
 func (r *randGen) allocAddr(s *state, typ Type, dir Dir, size uint64, data Arg) *PointerArg {
+	_, isStruct := data.(*GroupArg)
+	if r.genKFuzzTest && isStruct {
+		size = KFuzzTestMaxInputSize
+	}
 	return MakePointerArg(typ, dir, s.ma.alloc(r, size, data.Type().Alignment()), data)
 }