util/deephash: fix map hashing to actually hash elements

Fixes #4868

Change-Id: I574fd139cb7f7033dd93527344e6aa0e625477c7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
(cherry picked from commit 36ea837736)

util/deephash/deephash.go

@@ -342,7 +342,7 @@ func (h *hasher) hashMap(v reflect.Value) {
 		e.SetIterValue(iter)
 		mh.h.reset()
 		mh.h.hashValue(k)
-		mh.h.hashValue(v)
+		mh.h.hashValue(e)
 		sum.xor(mh.h.sum())
 	}
 	h.bw.Write(append(h.scratch[:0], sum.sum[:]...)) // append into scratch to avoid heap allocation

util/deephash/deephash_test.go

@@ -132,6 +132,15 @@ func TestDeepHash(t *testing.T) {
 	}
 }
 
+// Tests that we actually hash map elements. Whoops.
+func TestIssue4868(t *testing.T) {
+	m1 := map[int]string{1: "foo"}
+	m2 := map[int]string{1: "bar"}
+	if Hash(m1) == Hash(m2) {
+		t.Error("bogus")
+	}
+}
+
 func getVal() []any {
 	return []any{
 		&wgcfg.Config{