all: use math/rand/v2 more

Updates #11058

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/cert.go

@@ -22,7 +22,7 @@ import (
 	"fmt"
 	"io"
 	"log"
-	insecurerand "math/rand"
+	randv2 "math/rand/v2"
 	"net"
 	"os"
 	"path/filepath"
@@ -212,7 +212,7 @@ func (b *LocalBackend) domainRenewalTimeByARI(cs certStore, pair *TLSCertKeyPair
 	// passed. Time is randomized per recommendation in
 	// https://datatracker.ietf.org/doc/draft-ietf-acme-ari/
 	start, end := ri.SuggestedWindow.Start, ri.SuggestedWindow.End
-	renewTime := start.Add(time.Duration(insecurerand.Int63n(int64(end.Sub(start)))))
+	renewTime := start.Add(randv2.N(end.Sub(start)))
 	return renewTime, nil
 }
 

ipn/ipnlocal/local.go

@@ -15,7 +15,7 @@ import (
 	"log"
 	"maps"
 	"math"
-	"math/rand"
+	"math/rand/v2"
 	"net"
 	"net/http"
 	"net/netip"
@@ -6650,12 +6650,12 @@ func pickWeighted(candidates []tailcfg.NodeView) []tailcfg.NodeView {
 
 // randomRegion is a selectRegionFunc that selects a uniformly random region.
 func randomRegion(regions views.Slice[int]) int {
-	return regions.At(rand.Intn(regions.Len()))
+	return regions.At(rand.IntN(regions.Len()))
 }
 
 // randomNode is a selectNodeFunc that returns a uniformly random node.
 func randomNode(nodes views.Slice[tailcfg.NodeView]) tailcfg.NodeView {
-	return nodes.At(rand.Intn(nodes.Len()))
+	return nodes.At(rand.IntN(nodes.Len()))
 }
 
 // minLatencyDERPRegion returns the region with the lowest latency value given the last netcheck report.

ipn/ipnlocal/profiles.go

@@ -5,10 +5,10 @@ package ipnlocal
 
 import (
 	"cmp"
+	"crypto/rand"
 	"encoding/json"
 	"errors"
 	"fmt"
-	"math/rand"
 	"runtime"
 	"slices"
 	"strings"