TLS client: Use Xray-core's built-in RootCAs by default (avoids maliciously injected CA in the OS) (#7105)

https://github.com/XTLS/Xray-core/pull/5532#issuecomment-3745598515
https://github.com/XTLS/Xray-core/pull/7098#issuecomment-6053012480
https://github.com/XTLS/Xray-core/pull/7105#issuecomment-6093006914

transport/internet/tls/config.go

@@ -19,6 +19,7 @@ import (
 	"github.com/xtls/xray-core/common/platform/filesystem"
 	"github.com/xtls/xray-core/common/protocol/tls/cert"
 	"github.com/xtls/xray-core/transport/internet"
+	"golang.org/x/crypto/x509roots/fallback/bundle"
 )
 
 var globalSessionCache = tls.NewLRUClientSessionCache(128)
@@ -578,3 +579,39 @@ func verifyChain(certs []*x509.Certificate, pinnedPeerCertSha256 [][]byte) (veri
 	}
 	return certNotFound, nil
 }
+
+var bundleCertPool = sync.OnceValue(func() *x509.CertPool {
+	pool := x509.NewCertPool()
+	for r := range bundle.Roots() {
+		cert, err := x509.ParseCertificate(r.Certificate)
+		if err != nil {
+			continue
+		}
+		if r.Constraint != nil {
+			pool.AddCertWithConstraint(cert, r.Constraint)
+		} else {
+			pool.AddCert(cert)
+		}
+	}
+	return pool
+})
+
+var systemCertPool = sync.OnceValue(func() *x509.CertPool {
+	pool, err := x509.SystemCertPool()
+	if err != nil {
+		// use bundle cert pool as fallback
+		pool = bundleCertPool()
+	}
+	return pool
+})
+
+// pool should not be modified directly, use CertPool.Clone() if needed.
+func loadCA(useSystem bool) *x509.CertPool {
+	var pool *x509.CertPool
+	if useSystem {
+		pool = systemCertPool()
+	} else {
+		pool = bundleCertPool()
+	}
+	return pool
+}

transport/internet/tls/config.pb.go

@@ -206,6 +206,7 @@ type Config struct {
 	EchConfigList        string                 `protobuf:"bytes,19,opt,name=ech_config_list,json=echConfigList,proto3" json:"ech_config_list,omitempty"`
 	EchSocketSettings    *internet.SocketConfig `protobuf:"bytes,21,opt,name=ech_socket_settings,json=echSocketSettings,proto3" json:"ech_socket_settings,omitempty"`
 	PinnedPeerCertSha256 [][]byte               `protobuf:"bytes,22,rep,name=pinned_peer_cert_sha256,json=pinnedPeerCertSha256,proto3" json:"pinned_peer_cert_sha256,omitempty"`
+	UseSystemCa          bool                   `protobuf:"varint,23,opt,name=use_system_ca,json=useSystemCa,proto3" json:"use_system_ca,omitempty"`
 	unknownFields        protoimpl.UnknownFields
 	sizeCache            protoimpl.SizeCache
 }
@@ -359,6 +360,13 @@ func (x *Config) GetPinnedPeerCertSha256() [][]byte {
 	return nil
 }
 
+func (x *Config) GetUseSystemCa() bool {
+	if x != nil {
+		return x.UseSystemCa
+	}
+	return false
+}
+
 var File_transport_internet_tls_config_proto protoreflect.FileDescriptor
 
 const file_transport_internet_tls_config_proto_rawDesc = "" +
@@ -377,7 +385,7 @@ const file_transport_internet_tls_config_proto_rawDesc = "" +
 	"\x05Usage\x12\x10\n" +
 	"\fENCIPHERMENT\x10\x00\x12\x14\n" +
 	"\x10AUTHORITY_VERIFY\x10\x01\x12\x13\n" +
-	"\x0fAUTHORITY_ISSUE\x10\x02\"\xa6\x06\n" +
+	"\x0fAUTHORITY_ISSUE\x10\x02\"\xca\x06\n" +
 	"\x06Config\x12J\n" +
 	"\vcertificate\x18\x02 \x03(\v2(.xray.transport.internet.tls.CertificateR\vcertificate\x12\x1f\n" +
 	"\vserver_name\x18\x03 \x01(\tR\n" +
@@ -398,7 +406,8 @@ const file_transport_internet_tls_config_proto_rawDesc = "" +
 	"\x0fech_server_keys\x18\x12 \x01(\fR\rechServerKeys\x12&\n" +
 	"\x0fech_config_list\x18\x13 \x01(\tR\rechConfigList\x12U\n" +
 	"\x13ech_socket_settings\x18\x15 \x01(\v2%.xray.transport.internet.SocketConfigR\x11echSocketSettings\x125\n" +
-	"\x17pinned_peer_cert_sha256\x18\x16 \x03(\fR\x14pinnedPeerCertSha256Bs\n" +
+	"\x17pinned_peer_cert_sha256\x18\x16 \x03(\fR\x14pinnedPeerCertSha256\x12\"\n" +
+	"\ruse_system_ca\x18\x17 \x01(\bR\vuseSystemCaBs\n" +
 	"\x1fcom.xray.transport.internet.tlsP\x01Z0github.com/xtls/xray-core/transport/internet/tls\xaa\x02\x1bXray.Transport.Internet.Tlsb\x06proto3"
 
 var (

transport/internet/tls/config.proto

@@ -86,4 +86,6 @@ message Config {
   SocketConfig ech_socket_settings = 21;
 
   repeated bytes pinned_peer_cert_sha256 = 22;
+
+  bool use_system_ca = 23;
 }

transport/internet/tls/config_other.go

@@ -5,50 +5,23 @@ package tls
 
 import (
 	"crypto/x509"
-	"sync"
 
 	"github.com/xtls/xray-core/common/errors"
 )
 
-type rootCertsCache struct {
-	sync.Mutex
-	pool *x509.CertPool
-}
-
-func (c *rootCertsCache) load() (*x509.CertPool, error) {
-	c.Lock()
-	defer c.Unlock()
-
-	if c.pool != nil {
-		return c.pool, nil
-	}
-
-	pool, err := x509.SystemCertPool()
-	if err != nil {
-		return nil, err
-	}
-	c.pool = pool
-	return pool, nil
-}
-
-var rootCerts rootCertsCache
-
 func (c *Config) getCertPool() (*x509.CertPool, error) {
 	if c.DisableSystemRoot {
 		return c.loadSelfCertPool()
 	}
 
 	if len(c.Certificate) == 0 {
-		return rootCerts.load()
+		return loadCA(c.UseSystemCa), nil
 	}
 
-	pool, err := x509.SystemCertPool()
-	if err != nil {
-		return nil, errors.New("system root").Base(err)
-	}
+	pool := loadCA(c.UseSystemCa).Clone()
 	for _, cert := range c.Certificate {
 		if !pool.AppendCertsFromPEM(cert.Certificate) {
-			return nil, errors.New("append cert to root").Base(err)
+			return nil, errors.New("append cert to root")
 		}
 	}
 	return pool, nil

transport/internet/tls/config_windows.go

@@ -3,12 +3,30 @@
 
 package tls
 
-import "crypto/x509"
+import (
+	"crypto/x509"
+
+	"github.com/xtls/xray-core/common/errors"
+)
 
 func (c *Config) getCertPool() (*x509.CertPool, error) {
 	if c.DisableSystemRoot {
 		return c.loadSelfCertPool()
 	}
 
-	return nil, nil
+	// Windows should keep RootCAs nil for using the system CA.
+	if c.UseSystemCa && len(c.Certificate) == 0 {
+		return nil, nil
+	}
+
+	if len(c.Certificate) == 0 {
+		return loadCA(c.UseSystemCa), nil
+	}
+	pool := loadCA(c.UseSystemCa).Clone()
+	for _, cert := range c.Certificate {
+		if !pool.AppendCertsFromPEM(cert.Certificate) {
+			return nil, errors.New("failed to append cert")
+		}
+	}
+	return pool, nil
 }