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fix data race in code for logging login attempts

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logging of login attempts happens in the background, because we don't want to
block regular operation with disk since for such logging. however, when a line
is logged, we evaluate some attributes of a connection, notably the username.
but about when we do authentication, we change the username on a connection. so
we were reading and writing at the same time. this is now fixed by evaluating
the attributes before we pass off the logger to the goroutine.

found by the go race detector.
This commit is contained in:
Mechiel Lukkien
2025-02-19 15:23:19 +01:00
parent de6262b90a
commit cbe5bb235c
8 changed files with 89 additions and 48 deletions
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20
smtpserver/server.go
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@ -338,7 +338,7 @@ type conn struct {
localIP net.IP
remoteIP net.IP
hostname dns.Domain
log mlog.Log
log mlog.Log // Used for all synchronous logging on this connection, see logbg for logging in a separate goroutine.
maxMessageSize int64
requireTLSForAuth bool
requireTLSForDelivery bool // If set, delivery is only allowed with TLS (STARTTLS), except if delivery is to a TLS reporting address.
@ -401,6 +401,18 @@ func isClosed(err error) bool {
return errors.Is(err, errIO) || moxio.IsClosed(err)
}
// Logbg returns a logger for logging in the background (in a goroutine), eg for
// logging LoginAttempts. The regular c.log has a handler that evaluates fields on
// the connection at time of logging, which may happen at the same time as
// modifications to those fields.
func (c *conn) logbg() mlog.Log {
log := mlog.New("smtpserver", nil).WithCid(c.cid)
if c.username != "" {
log = log.With(slog.String("username", c.username))
}
return log
}
// loginAttempt initializes a store.LoginAttempt, for adding to the store after
// filling in the results and other details.
func (c *conn) loginAttempt(useTLS bool, authMech string) store.LoginAttempt {
@ -483,6 +495,7 @@ func (c *conn) tlsClientAuthVerifyPeerCertParsed(cert *x509.Certificate) error {
// Get TLS connection state in goroutine because we are called while performing the
// TLS handshake, which already has the tls connection locked.
conn := c.conn.(*tls.Conn)
logbg := c.logbg() // Evaluate attributes now, can't do it in goroutine.
go func() {
defer func() {
// In case of panic don't take the whole program down.
@ -496,7 +509,7 @@ func (c *conn) tlsClientAuthVerifyPeerCertParsed(cert *x509.Certificate) error {
state := conn.ConnectionState()
la.TLS = store.LoginAttemptTLS(&state)
store.LoginAttemptAdd(context.Background(), c.log, la)
store.LoginAttemptAdd(context.Background(), logbg, la)
}()
if la.Result == store.AuthSuccess {
@ -896,6 +909,7 @@ func serve(listenerName string, cid int64, hostname dns.Domain, tlsConfig *tls.C
firstTimeSenderDelay: firstTimeSenderDelay,
}
var logmutex sync.Mutex
// Also see (and possibly update) c.logbg, for logging in a goroutine.
c.log = mlog.New("smtpserver", nil).WithFunc(func() []slog.Attr {
logmutex.Lock()
defer logmutex.Unlock()
@ -1294,7 +1308,7 @@ func (c *conn) cmdAuth(p *parser) {
la := c.loginAttempt(true, "")
defer func() {
store.LoginAttemptAdd(context.Background(), c.log, la)
store.LoginAttemptAdd(context.Background(), c.logbg(), la)
if la.Result == store.AuthSuccess {
mox.LimiterFailedAuth.Reset(c.remoteIP, time.Now())
} else if !missingDerivedSecrets {