Fix corrupted wal segment panic on 32 bit systems

CHANGELOG.md

@@ -73,6 +73,7 @@
 - [#8900](https://github.com/influxdata/influxdb/issues/8900): Don't assume `which` is present in package post-install script.
 - [#8908](https://github.com/influxdata/influxdb/issues/8908): Fix missing man pages in new packaging output
 - [#8909](https://github.com/influxdata/influxdb/issues/8909): Fix use of `INFLUXD_OPTS` in service file
+- [#8952](https://github.com/influxdata/influxdb/issues/8952): Fix WAL panic: runtime error: makeslice: cap out of range
 
 ## v1.3.4 [unreleased]
 

tsdb/engine/tsm1/wal.go

@@ -772,6 +772,10 @@ func (w *WriteWALEntry) UnmarshalBinary(b []byte) error {
 		nvals := int(binary.BigEndian.Uint32(b[i : i+4]))
 		i += 4
 
+		if nvals <= 0 || nvals > len(b) {
+			return ErrWALCorrupt
+		}
+
 		switch typ {
 		case float64EntryType:
 			if i+16*nvals > len(b) {

tsdb/engine/tsm1/wal_test.go

@@ -603,6 +603,52 @@ func TestWALWriter_Corrupt(t *testing.T) {
 	}
 }
 
+// Reproduces a `panic: runtime error: makeslice: cap out of range` when run with
+// GOARCH=386 go test -run TestWALSegmentReader_Corrupt -v ./tsdb/engine/tsm1/
+func TestWALSegmentReader_Corrupt(t *testing.T) {
+	dir := MustTempDir()
+	defer os.RemoveAll(dir)
+	f := MustTempFile(dir)
+	w := tsm1.NewWALSegmentWriter(f)
+
+	p4 := tsm1.NewValue(1, "string")
+
+	values := map[string][]tsm1.Value{
+		"cpu,host=A#!~#string": []tsm1.Value{p4, p4},
+	}
+
+	entry := &tsm1.WriteWALEntry{
+		Values: values,
+	}
+
+	typ, b := mustMarshalEntry(entry)
+
+	// This causes the nvals field to overflow on 32 bit systems which produces a
+	// negative count and a panic when reading the segment.
+	b[25] = 255
+
+	if err := w.Write(typ, b); err != nil {
+		fatal(t, "write points", err)
+	}
+
+	if err := w.Flush(); err != nil {
+		fatal(t, "flush", err)
+	}
+
+	// Create the WAL segment reader.
+	if _, err := f.Seek(0, io.SeekStart); err != nil {
+		fatal(t, "seek", err)
+	}
+
+	r := tsm1.NewWALSegmentReader(f)
+	defer r.Close()
+
+	// Try to decode two entries.
+	for r.Next() {
+		r.Read()
+	}
+}
+
 func TestWriteWALSegment_UnmarshalBinary_WriteWALCorrupt(t *testing.T) {
 	p1 := tsm1.NewValue(1, 1.1)
 	p2 := tsm1.NewValue(1, int64(1))