fix bug with concurrent math/rand.Rand.Read

firstly by using crypto/rand in those cases. and secondly by putting a lock
around the Read (though it isn't used at the moment).

found while working while implementing sending tls reports.

dmarcdb/eval.go

@@ -272,7 +272,7 @@ func RemoveEvaluationsDomain(ctx context.Context, domain dns.Domain) error {
 	return err
 }
 
-var jitterRand = mox.NewRand()
+var jitterRand = mox.NewPseudoRand()
 
 // time to sleep until next whole hour t, replaced by tests.
 // Jitter so we don't cause load at exactly whole hours, other processes may

mox-/msgid.go

@@ -1,14 +1,13 @@
 package mox
 
 import (
+	cryptorand "crypto/rand"
 	"encoding/base64"
 )
 
-var messageIDRand = NewRand()
-
 // MessageIDGen returns a generated unique random Message-Id value, excluding <>.
 func MessageIDGen(smtputf8 bool) string {
 	buf := make([]byte, 16)
-	messageIDRand.Read(buf)
+	cryptorand.Read(buf)
 	return base64.RawURLEncoding.EncodeToString(buf) + "@" + Conf.Static.HostnameDomain.XName(smtputf8)
 }

mox-/rand.go

@@ -5,11 +5,24 @@ import (
 	"encoding/binary"
 	"fmt"
 	mathrand "math/rand"
+	"sync"
 )
 
-// NewRand returns a new PRNG seeded with random bytes from crypto/rand.
-func NewRand() *mathrand.Rand {
-	return mathrand.New(mathrand.NewSource(CryptoRandInt()))
+type rand struct {
+	*mathrand.Rand
+	sync.Mutex
+}
+
+// NewPseudoRand returns a new PRNG seeded with random bytes from crypto/rand.
+func NewPseudoRand() *rand {
+	return &rand{Rand: mathrand.New(mathrand.NewSource(CryptoRandInt()))}
+}
+
+// Read can be called concurrently.
+func (r *rand) Read(buf []byte) (int, error) {
+	r.Lock()
+	defer r.Unlock()
+	return r.Rand.Read(buf)
 }
 
 // CryptoRandInt returns a cryptographically random number.

queue/queue.go

@@ -61,7 +61,7 @@ var (
 	)
 )
 
-var jitter = mox.NewRand()
+var jitter = mox.NewPseudoRand()
 
 var DBTypes = []any{Msg{}} // Types stored in DB.
 var DB *bstore.DB          // Exported for making backups.

quickstart.go

@@ -40,11 +40,19 @@ import (
 var moxService string
 
 func pwgen() string {
-	rand := mox.NewRand()
 	chars := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*-_;:,<.>/"
 	s := ""
+	buf := make([]byte, 1)
 	for i := 0; i < 12; i++ {
-		s += string(chars[rand.Intn(len(chars))])
+		for {
+			cryptorand.Read(buf)
+			i := int(buf[0])
+			if i+len(chars) > 255 {
+				continue // Prevent bias.
+			}
+			s += string(chars[i%len(chars)])
+			break
+		}
 	}
 	return s
 }

smtpserver/server.go

@@ -168,7 +168,7 @@ var (
 	)
 )
 
-var jitterRand = mox.NewRand()
+var jitterRand = mox.NewPseudoRand()
 
 func durationDefault(delay *time.Duration, def time.Duration) time.Duration {
 	if delay == nil {

store/account.go

@@ -24,6 +24,7 @@ package store
 import (
 	"context"
 	"crypto/md5"
+	cryptorand "crypto/rand"
 	"crypto/sha1"
 	"crypto/sha256"
 	"encoding"
@@ -74,8 +75,6 @@ var (
 	ErrAccountUnknown     = errors.New("no such account")
 )
 
-var subjectpassRand = mox.NewRand()
-
 var DefaultInitialMailboxes = config.InitialMailboxes{
 	SpecialUse: config.SpecialUseMailboxes{
 		Sent:    "Sent",
@@ -1460,8 +1459,12 @@ func (a *Account) Subjectpass(email string) (key string, err error) {
 		}
 		key = ""
 		const chars = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
-		for i := 0; i < 16; i++ {
-			key += string(chars[subjectpassRand.Intn(len(chars))])
+		buf := make([]byte, 16)
+		if _, err := cryptorand.Read(buf); err != nil {
+			return err
+		}
+		for _, b := range buf {
+			key += string(chars[int(b)%len(chars)])
 		}
 		v.Key = key
 		return tx.Insert(&v)