crypto/tls: randomly generate ticket_age_add

# AWS EKS
Backported To: go-1.16.15-eks
Backported On: Tue, 04 Oct 2022
Backported By: budris@amazon.com
Backported From: release-branch.go1.17
EKS Patch Source Commit: danbudris@3beb7c1
Upstream Source Commit: golang@c15a8e2

# Original Information

As required by RFC 8446, section 4.6.1, ticket_age_add now holds a
random 32-bit value. Before this change, this value was always set
to 0.

This change also documents the reasoning for always setting
ticket_nonce to 0. The value ticket_nonce must be unique per
connection, but we only ever send one ticket per connection.

Updates golang#52814
Fixes golang#52832
Fixes CVE-2022-30629

Change-Id: I6c2fc6ca0376b7b968abd59d6d3d3854c1ab68bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/405994
Reviewed-by: Tatiana Bradley <tatiana@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Run-TryBot: Tatiana Bradley <tatiana@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit fe4de36)
Reviewed-on: https://go-review.googlesource.com/c/go/+/408574
Run-TryBot: Roland Shoemaker <roland@golang.org>

src/crypto/tls/handshake_server_tls13.go

@@ -9,6 +9,7 @@ import (
 	"crypto"
 	"crypto/hmac"
 	"crypto/rsa"
+	"encoding/binary"
 	"errors"
 	"hash"
 	"io"
@@ -755,6 +756,19 @@ func (hs *serverHandshakeStateTLS13) sendSessionTickets() error {
 	}
 	m.lifetime = uint32(maxSessionTicketLifetime / time.Second)
 
+	// ticket_age_add is a random 32-bit value. See RFC 8446, section 4.6.1
+	// The value is not stored anywhere; we never need to check the ticket age
+	// because 0-RTT is not supported.
+	ageAdd := make([]byte, 4)
+	_, err = hs.c.config.rand().Read(ageAdd)
+	if err != nil {
+		return err
+	}
+	m.ageAdd = binary.LittleEndian.Uint32(ageAdd)
+
+	// ticket_nonce, which must be unique per connection, is always left at
+	// zero because we only ever send one ticket per connection.
+
 	if _, err := c.writeRecord(recordTypeHandshake, m.marshal()); err != nil {
 		return err
 	}