Implement TLS fingerprint pinning

Closes: https://todo.sr.ht/~emersion/soju/56

database/database.go

@@ -130,6 +130,7 @@ type Network struct {
 	Realname        string
 	Pass            string
 	ConnectCommands []string
+	CertFP          string
 	SASL            SASL
 	AutoAway        bool
 	Enabled         bool

database/postgres.go

@@ -44,6 +44,7 @@ CREATE TABLE "Network" (
 	nick VARCHAR(255),
 	username VARCHAR(255),
 	realname VARCHAR(255),
+	certfp TEXT,
 	pass VARCHAR(255),
 	connect_commands VARCHAR(1023),
 	sasl_mechanism sasl_mechanism,
@@ -165,6 +166,7 @@ var postgresMigrations = []string{
 		SET NOT NULL;
 	`,
 	`ALTER TABLE "Network" ADD COLUMN auto_away BOOLEAN NOT NULL DEFAULT TRUE`,
+	`ALTER TABLE "Network" ADD COLUMN certfp TEXT`,
 }
 
 type PostgresDB struct {
@@ -380,7 +382,7 @@ func (db *PostgresDB) ListNetworks(ctx context.Context, userID int64) ([]Network
 	defer cancel()
 
 	rows, err := db.db.QueryContext(ctx, `
-		SELECT id, name, addr, nick, username, realname, pass, connect_commands, sasl_mechanism,
+		SELECT id, name, addr, nick, username, realname, certfp, pass, connect_commands, sasl_mechanism,
 			sasl_plain_username, sasl_plain_password, sasl_external_cert, sasl_external_key, auto_away, enabled
 		FROM "Network"
 		WHERE "user" = $1`, userID)
@@ -392,9 +394,9 @@ func (db *PostgresDB) ListNetworks(ctx context.Context, userID int64) ([]Network
 	var networks []Network
 	for rows.Next() {
 		var net Network
-		var name, nick, username, realname, pass, connectCommands sql.NullString
+		var name, nick, username, realname, certfp, pass, connectCommands sql.NullString
 		var saslMechanism, saslPlainUsername, saslPlainPassword sql.NullString
-		err := rows.Scan(&net.ID, &name, &net.Addr, &nick, &username, &realname,
+		err := rows.Scan(&net.ID, &name, &net.Addr, &nick, &username, &realname, &certfp,
 			&pass, &connectCommands, &saslMechanism, &saslPlainUsername, &saslPlainPassword,
 			&net.SASL.External.CertBlob, &net.SASL.External.PrivKeyBlob, &net.AutoAway, &net.Enabled)
 		if err != nil {
@@ -404,6 +406,7 @@ func (db *PostgresDB) ListNetworks(ctx context.Context, userID int64) ([]Network
 		net.Nick = nick.String
 		net.Username = username.String
 		net.Realname = realname.String
+		net.CertFP = certfp.String
 		net.Pass = pass.String
 		if connectCommands.Valid {
 			net.ConnectCommands = strings.Split(connectCommands.String, "\r\n")
@@ -428,6 +431,7 @@ func (db *PostgresDB) StoreNetwork(ctx context.Context, userID int64, network *N
 	nick := toNullString(network.Nick)
 	netUsername := toNullString(network.Username)
 	realname := toNullString(network.Realname)
+	certfp := toNullString(network.CertFP)
 	pass := toNullString(network.Pass)
 	connectCommands := toNullString(strings.Join(network.ConnectCommands, "\r\n"))
 
@@ -450,23 +454,23 @@ func (db *PostgresDB) StoreNetwork(ctx context.Context, userID int64, network *N
 	var err error
 	if network.ID == 0 {
 		err = db.db.QueryRowContext(ctx, `
-			INSERT INTO "Network" ("user", name, addr, nick, username, realname, pass, connect_commands,
+			INSERT INTO "Network" ("user", name, addr, nick, username, realname, certfp, pass, connect_commands,
 				sasl_mechanism, sasl_plain_username, sasl_plain_password, sasl_external_cert,
 				sasl_external_key, auto_away, enabled)
-			VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15)
+			VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16)
 			RETURNING id`,
-			userID, netName, network.Addr, nick, netUsername, realname, pass, connectCommands,
+			userID, netName, network.Addr, nick, netUsername, realname, certfp, pass, connectCommands,
 			saslMechanism, saslPlainUsername, saslPlainPassword, network.SASL.External.CertBlob,
 			network.SASL.External.PrivKeyBlob, network.AutoAway, network.Enabled).Scan(&network.ID)
 	} else {
 		_, err = db.db.ExecContext(ctx, `
 			UPDATE "Network"
-			SET name = $2, addr = $3, nick = $4, username = $5, realname = $6, pass = $7,
+			SET name = $2, addr = $3, nick = $4, username = $5, realname = $6, certfp = $7, pass = $8,
-				connect_commands = $8, sasl_mechanism = $9, sasl_plain_username = $10,
+				connect_commands = $9, sasl_mechanism = $10, sasl_plain_username = $11,
-				sasl_plain_password = $11, sasl_external_cert = $12, sasl_external_key = $13,
+				sasl_plain_password = $12, sasl_external_cert = $13, sasl_external_key = $14,
 				auto_away = $14, enabled = $15
 			WHERE id = $1`,
-			network.ID, netName, network.Addr, nick, netUsername, realname, pass, connectCommands,
+			network.ID, netName, network.Addr, nick, netUsername, realname, certfp, pass, connectCommands,
 			saslMechanism, saslPlainUsername, saslPlainPassword, network.SASL.External.CertBlob,
 			network.SASL.External.PrivKeyBlob, network.AutoAway, network.Enabled)
 	}

database/sqlite.go

@@ -42,6 +42,7 @@ CREATE TABLE Network (
 	nick TEXT,
 	username TEXT,
 	realname TEXT,
+	certfp TEXT,
 	pass TEXT,
 	connect_commands TEXT,
 	sasl_mechanism TEXT,
@@ -250,6 +251,7 @@ var sqliteMigrations = []string{
 	`,
 	"ALTER TABLE User ADD COLUMN nick TEXT;",
 	"ALTER TABLE Network ADD COLUMN auto_away INTEGER NOT NULL DEFAULT 1;",
+	"ALTER TABLE Network ADD COLUMN certfp TEXT;",
 }
 
 type SqliteDB struct {
@@ -488,7 +490,7 @@ func (db *SqliteDB) ListNetworks(ctx context.Context, userID int64) ([]Network,
 	defer cancel()
 
 	rows, err := db.db.QueryContext(ctx, `
-		SELECT id, name, addr, nick, username, realname, pass,
+		SELECT id, name, addr, nick, username, realname, certfp, pass,
 			connect_commands, sasl_mechanism, sasl_plain_username, sasl_plain_password,
 			sasl_external_cert, sasl_external_key, auto_away, enabled
 		FROM Network
@@ -502,9 +504,9 @@ func (db *SqliteDB) ListNetworks(ctx context.Context, userID int64) ([]Network,
 	var networks []Network
 	for rows.Next() {
 		var net Network
-		var name, nick, username, realname, pass, connectCommands sql.NullString
+		var name, nick, username, realname, certfp, pass, connectCommands sql.NullString
 		var saslMechanism, saslPlainUsername, saslPlainPassword sql.NullString
-		err := rows.Scan(&net.ID, &name, &net.Addr, &nick, &username, &realname,
+		err := rows.Scan(&net.ID, &name, &net.Addr, &nick, &username, &realname, &certfp,
 			&pass, &connectCommands, &saslMechanism, &saslPlainUsername, &saslPlainPassword,
 			&net.SASL.External.CertBlob, &net.SASL.External.PrivKeyBlob, &net.AutoAway, &net.Enabled)
 		if err != nil {
@@ -514,6 +516,7 @@ func (db *SqliteDB) ListNetworks(ctx context.Context, userID int64) ([]Network,
 		net.Nick = nick.String
 		net.Username = username.String
 		net.Realname = realname.String
+		net.CertFP = certfp.String
 		net.Pass = pass.String
 		if connectCommands.Valid {
 			net.ConnectCommands = strings.Split(connectCommands.String, "\r\n")
@@ -556,6 +559,7 @@ func (db *SqliteDB) StoreNetwork(ctx context.Context, userID int64, network *Net
 		sql.Named("nick", toNullString(network.Nick)),
 		sql.Named("username", toNullString(network.Username)),
 		sql.Named("realname", toNullString(network.Realname)),
+		sql.Named("certfp", toNullString(network.CertFP)),
 		sql.Named("pass", toNullString(network.Pass)),
 		sql.Named("connect_commands", toNullString(strings.Join(network.ConnectCommands, "\r\n"))),
 		sql.Named("sasl_mechanism", saslMechanism),
@@ -575,7 +579,7 @@ func (db *SqliteDB) StoreNetwork(ctx context.Context, userID int64, network *Net
 		_, err = db.db.ExecContext(ctx, `
 			UPDATE Network
 			SET name = :name, addr = :addr, nick = :nick, username = :username,
-				realname = :realname, pass = :pass, connect_commands = :connect_commands,
+				realname = :realname, certfp = :certfp, pass = :pass, connect_commands = :connect_commands,
 				sasl_mechanism = :sasl_mechanism, sasl_plain_username = :sasl_plain_username, sasl_plain_password = :sasl_plain_password,
 				sasl_external_cert = :sasl_external_cert, sasl_external_key = :sasl_external_key,
 				auto_away = :auto_away, enabled = :enabled
@@ -583,10 +587,10 @@ func (db *SqliteDB) StoreNetwork(ctx context.Context, userID int64, network *Net
 	} else {
 		var res sql.Result
 		res, err = db.db.ExecContext(ctx, `
-			INSERT INTO Network(user, name, addr, nick, username, realname, pass,
+			INSERT INTO Network(user, name, addr, nick, username, realname, certfp, pass,
 				connect_commands, sasl_mechanism, sasl_plain_username,
 				sasl_plain_password, sasl_external_cert, sasl_external_key, auto_away, enabled)
-			VALUES (:user, :name, :addr, :nick, :username, :realname, :pass,
+			VALUES (:user, :name, :addr, :nick, :username, :realname, :certfp, :pass,
 				:connect_commands, :sasl_mechanism, :sasl_plain_username,
 				:sasl_plain_password, :sasl_external_cert, :sasl_external_key, :auto_away, :enabled)`,
 			args...)

doc/soju.1.scd

@@ -213,6 +213,12 @@ abbreviated form, for instance *network* can be abbreviated as *net* or just
 		Connect with the specified real name. By default, the account's realname
 		is used if set, otherwise the network's nickname is used.
 
+	*-certfp* <fingerprint>
+		Instead of using certificate authorities to check the server's TLS
+		certificate, check whether the server certificate matches the provided
+		fingerprint. This can be used to connect to servers using self-signed
+		certificates. The fingerprint format is SHA512.
+
 	*-nick* <nickname>
 		Connect with the specified nickname. By default, the account's username
 		is used.

service.go

@@ -201,7 +201,7 @@ func init() {
 		"network": {
 			children: serviceCommandSet{
 				"create": {
-					usage:  "-addr <addr> [-name name] [-username username] [-pass pass] [-realname realname] [-nick nick] [-auto-away auto-away] [-enabled enabled] [-connect-command command]...",
+					usage:  "-addr <addr> [-name name] [-username username] [-pass pass] [-realname realname] [-certfp fingerprint] [-nick nick] [-auto-away auto-away] [-enabled enabled] [-connect-command command]...",
 					desc:   "add a new network",
 					handle: handleServiceNetworkCreate,
 				},
@@ -210,7 +210,7 @@ func init() {
 					handle: handleServiceNetworkStatus,
 				},
 				"update": {
-					usage:  "[name] [-addr addr] [-name name] [-username username] [-pass pass] [-realname realname] [-nick nick] [-auto-away auto-away] [-enabled enabled] [-connect-command command]...",
+					usage:  "[name] [-addr addr] [-name name] [-username username] [-pass pass] [-realname realname] [-certfp fingerprint] [-nick nick] [-auto-away auto-away] [-enabled enabled] [-connect-command command]...",
 					desc:   "update a network",
 					handle: handleServiceNetworkUpdate,
 				},
@@ -435,9 +435,9 @@ func getNetworkFromArg(dc *downstreamConn, params []string) (*network, []string,
 
 type networkFlagSet struct {
 	*flag.FlagSet
-	Addr, Name, Nick, Username, Pass, Realname *string
+	Addr, Name, Nick, Username, Pass, Realname, CertFP *string
-	AutoAway, Enabled                          *bool
+	AutoAway, Enabled                                  *bool
-	ConnectCommands                            []string
+	ConnectCommands                                    []string
 }
 
 func newNetworkFlagSet() *networkFlagSet {
@@ -448,6 +448,7 @@ func newNetworkFlagSet() *networkFlagSet {
 	fs.Var(stringPtrFlag{&fs.Username}, "username", "")
 	fs.Var(stringPtrFlag{&fs.Pass}, "pass", "")
 	fs.Var(stringPtrFlag{&fs.Realname}, "realname", "")
+	fs.Var(stringPtrFlag{&fs.CertFP}, "fingerprint", "")
 	fs.Var(boolPtrFlag{&fs.AutoAway}, "auto-away", "")
 	fs.Var(boolPtrFlag{&fs.Enabled}, "enabled", "")
 	fs.Var((*stringSliceFlag)(&fs.ConnectCommands), "connect-command", "")
@@ -484,6 +485,19 @@ func (fs *networkFlagSet) update(network *database.Network) error {
 	if fs.Realname != nil {
 		network.Realname = *fs.Realname
 	}
+	if fs.CertFP != nil {
+		certFP := strings.ReplaceAll(*fs.CertFP, ":", "")
+		if _, err := hex.DecodeString(certFP); err != nil {
+			return fmt.Errorf("the certificate fingerprint must be hex-encoded")
+		}
+		if len(certFP) == 64 {
+			network.CertFP = "sha-256:" + certFP
+		} else if len(certFP) == 128 {
+			network.CertFP = "sha-512:" + certFP
+		} else {
+			return fmt.Errorf("the certificate fingerprint must be a SHA256 or SHA512 hash")
+		}
+	}
 	if fs.AutoAway != nil {
 		network.AutoAway = *fs.AutoAway
 	}

upstream.go

@@ -4,9 +4,11 @@ import (
 	"context"
 	"crypto"
 	"crypto/sha256"
+	"crypto/sha512"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/base64"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"io"
@@ -285,6 +287,40 @@ func connectToUpstream(ctx context.Context, network *network) (*upstreamConn, er
 			logger.Printf("using TLS client certificate %x", sha256.Sum256(network.SASL.External.CertBlob))
 		}
 
+		if network.CertFP != "" {
+			tlsConfig.InsecureSkipVerify = true
+			tlsConfig.VerifyPeerCertificate = func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error {
+				if len(rawCerts) == 0 {
+					return fmt.Errorf("the server didn't present any TLS certificate")
+				}
+
+				parts := strings.SplitN(network.CertFP, ":", 2)
+				algo, localCertFP := parts[0], parts[1]
+
+				for _, rawCert := range rawCerts {
+					var remoteCertFP string
+					switch algo {
+					case "sha-512":
+						sum := sha512.Sum512(rawCert)
+						remoteCertFP = hex.EncodeToString(sum[:])
+					case "sha-256":
+						sum := sha256.Sum256(rawCert)
+						remoteCertFP = hex.EncodeToString(sum[:])
+					}
+
+					if remoteCertFP == localCertFP {
+						return nil // fingerprints match
+					}
+				}
+
+				// Fingerprints don't match, let's give the user a fingerprint
+				// they can use to connect
+				sum := sha512.Sum512(rawCerts[0])
+				remoteCertFP := hex.EncodeToString(sum[:])
+				return fmt.Errorf("the configured TLS certificate fingerprint doesn't match the server's - %s", remoteCertFP)
+			}
+		}
+
 		netConn, err = dialer.DialContext(ctx, "tcp", addr)
 		if err != nil {
 			return nil, fmt.Errorf("failed to dial %q: %v", addr, err)