fuzz found a bug

.github/workflows/golangci-lint.yml

@@ -12,7 +12,7 @@ jobs:
         uses: golangci/golangci-lint-action@v2
         with:
           # Required: the version of golangci-lint is required and must be specified without patch version: we always use the latest patch version.
-          version: v1.59
+          version: v1.63.4
 
           # Optional: working directory, useful for monorepos
           # working-directory: somedir

eazy_test.go

@@ -1311,11 +1311,17 @@ func FuzzWriter(f *testing.F) {
 		[]byte("aaaaaaaaaaabaaaaaaaaaaaa"),
 	)
 
+	var wbuf, rbuf bytes.Buffer
+	buf := make([]byte, 16)
+
+	w := NewWriter(nil, 512, 32)
+	r := NewReader(nil)
+
 	f.Fuzz(func(t *testing.T, p0, p1, p2 []byte) {
-		var wbuf, rbuf bytes.Buffer
-		buf := make([]byte, 16)
+		wbuf.Reset()
+		rbuf.Reset()
 
-		w := NewWriter(&wbuf, 512, 32)
+		w.Reset(&wbuf)
 
 		for _, p := range [][]byte{p0, p1, p2} {
 			n, err := w.Write(p)
@@ -1329,12 +1335,13 @@ func FuzzWriter(f *testing.F) {
 				return
 			}
 
+			t.Logf("input:\n%4x: %q\n%4x: %q\n%4x: %q", len(p0), p0, len(p1), p1, len(p2), p2)
 			t.Logf("encoded dump\n%s", Dump(wbuf.Bytes()))
 
 			panic(p)
 		}()
 
-		r := NewReaderBytes(wbuf.Bytes())
+		r.Reset(&wbuf)
 
 		m, err := io.CopyBuffer(&rbuf, r, buf)
 		assert.NoError(t, err)
@@ -1370,10 +1377,14 @@ func FuzzReader(f *testing.F) {
 	f.Add([]byte{Meta, MetaVer, 1, Meta, MetaReset, 6, Literal | 3, 'a', 'b', 'c'})
 	f.Add([]byte{Meta, MetaVer, 1, Meta, MetaReset, 6, Literal | 3, 'a', 'b', 'c', Copy | 3, 0})
 
+	var h, b BufReader
+	r := NewReader(nil)
+	w := NewDumper(nil)
+
 	f.Fuzz(func(t *testing.T, p []byte) {
-		b := BufReader{Buf: p}
-		r := NewReader(&b)
-		w := NewDumper(nil)
+		h.Reset(header)
+		b.Reset(p)
+		r.Reset(&b)
 
 		_, err := io.Copy(w, io.MultiReader(
 			&BufReader{Buf: header},
@@ -1503,6 +1514,11 @@ func (b *Buf) Write(p []byte) (int, error) {
 	return len(p), nil
 }
 
+func (b *BufReader) Reset(p []byte) {
+	b.Buf = p
+	b.R = 0
+}
+
 func (b *BufReader) Read(p []byte) (int, error) {
 	n := copy(p, b.Buf[b.R:])
 	b.R += n

reader.go

@@ -185,6 +185,9 @@ func (r *Reader) read(p []byte, st int) (n, i int, err error) {
 		// ^ 0       ^ run          ^ end   // p pos
 
 		run := int(r.pos) - r.off
+		if run > len(p) {
+			run = len(p)
+		}
 
 		for j := 0; j < run; {
 			j += copy(p[j:run], r.block[(r.off+j)&r.mask:])
@@ -664,7 +667,7 @@ func (w *Dumper) Write(p []byte) (i int, err error) { //nolint:gocognit
 				w.r.d.Ver = int(p[i])
 			}
 
-			w.b = fmt.Appendf(w.b, "meta %2x %x  %q\n", meta>>3, l, p[i:i+l])
+			w.b = fmt.Appendf(w.b, "meta %2x %x  %-8q  % [3]x\n", meta>>3, l, p[i:i+l])
 
 			if w.Debug != nil {
 				w.Debug(w.r.boff+int64(st), w.r.boff+int64(i), w.r.pos, 'm', l, meta)

testdata/fuzz/FuzzReader/50a1dcccf68df51c

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("\x80\x10\x0f\x0f0 \x010\x00\x00\x00\x100000000\xd90\xd90\xd90\xd90\xd90\xd9_\xd9!ԁ\xbe\x83\xfe\xd90\xd9\x00\xff0\xd9_\xd9!")

testdata/fuzz/FuzzWriter/aa21c93f4bd24cfa

@@ -0,0 +1,4 @@
+go test fuzz v1
+[]byte("0x\x00\x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000")
+[]byte("00000")
+[]byte("\x00x\x00\x00x\x00\x00x\x00")

writer.go

@@ -164,7 +164,7 @@ func (w *Writer) init(bs, hs int) {
 	}
 
 	if (hs-1)&hs != 0 || hs < 4 {
-		panic("hash table size must be a power of two (hs > 4)")
+		panic("hash table size must be a power of two (hs >= 4)")
 	}
 
 	w.mask = bs - 1