Validate connection security properties

Author: fulghum

sql/mysql_db/auth.go

@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"crypto/sha1"
 	"encoding/hex"
+	"fmt"
 	"net"
 
 	"github.com/dolthub/vitess/go/mysql"
@@ -107,7 +108,7 @@ var _ mysql.CachingStorage = (*noopCachingStorage)(nil)
 //
 // This implementation also handles authentication when a client doesn't send an auth response and
 // the associated user account does not have a password set.
-func (n noopCachingStorage) UserEntryWithCacheHash(_ *mysql.Conn, _ []byte, user string, authResponse []byte, remoteAddr net.Addr) (mysql.Getter, mysql.CacheState, error) {
+func (n noopCachingStorage) UserEntryWithCacheHash(conn *mysql.Conn, _ []byte, user string, authResponse []byte, remoteAddr net.Addr) (mysql.Getter, mysql.CacheState, error) {
 	db := n.db
 
 	// If there is no mysql database of user info, then don't approve or reject, since we can't look at
@@ -131,7 +132,12 @@ func (n noopCachingStorage) UserEntryWithCacheHash(_ *mysql.Conn, _ []byte, user
 
 		userEntry := db.GetUser(rd, user, host, false)
 		if userEntry == nil || userEntry.Locked {
-			return nil, mysql.AuthRejected, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+			return nil, mysql.AuthRejected, newAccessDeniedError(user)
+		}
+
+		// validate any extra connection security requirements, such as SSL or a client cert
+		if err = validateConnectionSecurity(userEntry, conn); err != nil {
+			return nil, mysql.AuthRejected, err
 		}
 
 		if userEntry.AuthString == "" {
@@ -166,7 +172,7 @@ var _ mysql.PlainTextStorage = (*sha2PlainTextStorage)(nil)
 
 // UserEntryWithPassword implements the mysql.PlainTextStorage interface.
 // The auth framework in Vitess also passes in user certificates, but we don't support that feature yet.
-func (s sha2PlainTextStorage) UserEntryWithPassword(_ *mysql.Conn, user string, password string, remoteAddr net.Addr) (mysql.Getter, error) {
+func (s sha2PlainTextStorage) UserEntryWithPassword(conn *mysql.Conn, user string, password string, remoteAddr net.Addr) (mysql.Getter, error) {
 	db := s.db
 
 	host, err := extractHostAddress(remoteAddr)
@@ -183,7 +189,12 @@ func (s sha2PlainTextStorage) UserEntryWithPassword(_ *mysql.Conn, user string,
 
 	userEntry := db.GetUser(rd, user, host, false)
 	if userEntry == nil || userEntry.Locked {
-		return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+		return nil, newAccessDeniedError(userEntry.User)
+	}
+
+	// validate any extra connection security requirements, such as SSL or a client cert
+	if err = validateConnectionSecurity(userEntry, conn); err != nil {
+		return nil, err
 	}
 
 	if len(userEntry.AuthString) > 0 {
@@ -202,12 +213,12 @@ func (s sha2PlainTextStorage) UserEntryWithPassword(_ *mysql.Conn, user string,
 		}
 
 		if userEntry.AuthString != string(authString) {
-			return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+			return nil, newAccessDeniedError(user)
 		}
 	} else if len(password) > 0 {
 		// password is nil or empty, therefore no password is set
 		// a password was given and the account has no password set, therefore access is denied
-		return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+		return nil, newAccessDeniedError(user)
 	}
 
 	return sql.MysqlConnectionUser{User: userEntry.User, Host: userEntry.Host}, nil
@@ -269,8 +280,7 @@ func (f extendedAuthPlainTextStorage) UserEntryWithPassword(conn *mysql.Conn, us
 			"Access denied for user '%v': %v", user, err)
 	}
 	if !authed {
-		return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError,
-			"Access denied for user '%v'", user)
+		return nil, newAccessDeniedError(user)
 	}
 	return connUser, nil
 }
@@ -329,7 +339,7 @@ var _ mysql.HashStorage = (*nativePasswordHashStorage)(nil)
 
 // UserEntryWithHash implements the mysql.HashStorage interface. This implementation is called by the MySQL
 // native password auth method to validate a password hash with the user's stored password hash.
-func (nphs *nativePasswordHashStorage) UserEntryWithHash(_ *mysql.Conn, salt []byte, user string, authResponse []byte, remoteAddr net.Addr) (mysql.Getter, error) {
+func (nphs *nativePasswordHashStorage) UserEntryWithHash(conn *mysql.Conn, salt []byte, user string, authResponse []byte, remoteAddr net.Addr) (mysql.Getter, error) {
 	db := nphs.db
 
 	host, err := extractHostAddress(remoteAddr)
@@ -346,21 +356,83 @@ func (nphs *nativePasswordHashStorage) UserEntryWithHash(_ *mysql.Conn, salt []b
 
 	userEntry := db.GetUser(rd, user, host, false)
 	if userEntry == nil || userEntry.Locked {
-		return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+		return nil, newAccessDeniedError(user)
 	}
+
+	// validate any extra connection security requirements, such as SSL or a client cert
+	if err = validateConnectionSecurity(userEntry, conn); err != nil {
+		return nil, err
+	}
+
 	if len(userEntry.AuthString) > 0 {
 		if !validateMysqlNativePassword(authResponse, salt, userEntry.AuthString) {
-			return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+			return nil, newAccessDeniedError(user)
 		}
 	} else if len(authResponse) > 0 {
 		// password is nil or empty, therefore no password is set
 		// a password was given and the account has no password set, therefore access is denied
-		return nil, mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", user)
+		return nil, newAccessDeniedError(user)
 	}
 
 	return sql.MysqlConnectionUser{User: userEntry.User, Host: userEntry.Host}, nil
 }
 
+// validateConnectionSecurity examines the security properties of |conn| (e.g. TLS,
+// selected cipher, X509 client certs) and validates specific connection properties
+// based on what |userEntry| has configured. An error is returned if any validation
+// issues were detected, otherwise nil is returned.
+func validateConnectionSecurity(userEntry *User, conn *mysql.Conn) error {
+	switch userEntry.SslType {
+	case "":
+		// No connection security validation needed
+		return nil
+	case "ANY":
+		// ANY indicates that we need any form of secure socket
+		if !conn.TLSEnabled() {
+			return newAccessDeniedError(userEntry.User)
+		}
+	case "X509":
+		// X509 means that a valid X509 client certificate is required
+		// NOTE: cert validation (e.g. expiration date, CA chain) is handled
+		//       in the Go networking stack, so long as tls.VerifyClientCertIfGiven
+		//       is specified in the TLS configuration for the server.
+		clientCerts := conn.GetTLSClientCerts()
+		if len(clientCerts) == 0 {
+			return newAccessDeniedError(userEntry.User)
+		}
+		// TODO: Do we need to do anything if there are multiple client certs provided?
+	case "SPECIFIED":
+		// Specified means that we have additional requirements on either the SSL cipher
+		// or the X509 cert, so we need to perform additional validation checks.
+		if userEntry.SslCipher != "" {
+			if !conn.TLSEnabled() {
+				return newAccessDeniedError(userEntry.User)
+			}
+			// TODO: validate the ssl cipher
+			// TODO: How do we get the SSL cipher in use? What are valid values you can specify in MySQL?
+			return fmt.Errorf("SSL cipher validation not supported yet")
+		}
+		if userEntry.X509Issuer != "" {
+			if len(conn.GetTLSClientCerts()) == 0 {
+				return newAccessDeniedError(userEntry.User)
+			}
+			// TODO: Validate the client cert issuer
+			return fmt.Errorf("X509 issuer validation not supported yet")
+		}
+		if userEntry.X509Subject != "" {
+			if len(conn.GetTLSClientCerts()) == 0 {
+				return newAccessDeniedError(userEntry.User)
+			}
+			// TODO: Validate the client cert subject
+			return fmt.Errorf("X509 subject validation not supported yet")
+		}
+	default:
+		return fmt.Errorf("unsupported ssl_type: %v", userEntry.SslType)
+	}
+
+	return nil
+}
+
 // userValidator implements the mysql.UserValidator interface. It looks up a user and host from the
 // associated mysql database (|db|) and validates that a user entry exists and that it is configured
 // for the specified authentication plugin (|authMethod|).
@@ -408,7 +480,13 @@ func (uv *userValidator) HandleUser(user string, remoteAddr net.Addr) bool {
 	}
 	userEntry := db.GetUser(rd, user, host, false)
 
-	return userEntry != nil && userEntry.Plugin == string(uv.authMethod)
+	// If we don't find a matching user, or we find one, but it's for a different auth method,
+	// then return false to indicate this auth method can't handle that user.
+	if userEntry == nil || userEntry.Plugin != string(uv.authMethod) {
+		return false
+	}
+
+	return true
 }
 
 // extractHostAddress extracts the host address from |addr|, checking to see if it is a unix socket, and if
@@ -429,6 +507,14 @@ func extractHostAddress(addr net.Addr) (host string, err error) {
 	return host, nil
 }
 
+// newAccessDeniedError returns an "access denied" error, including the |userName| trying to authenticate,
+// matching MySQL's error message. Note that MySQL tends to return a generic "access denied" error message
+// for authentication failures, without leaking more details about why so that attackers can't exploit that
+// information to determine how a user is configured for authentication.
+func newAccessDeniedError(userName string) error {
+	return mysql.NewSQLError(mysql.ERAccessDeniedError, mysql.SSAccessDeniedError, "Access denied for user '%v'", userName)
+}
+
 // validateMysqlNativePassword was taken from vitess and validates the password hash for the mysql_native_password
 // auth protocol. Note that this implementation has diverged slightly from the original code in Vitess.
 func validateMysqlNativePassword(authResponse, salt []byte, mysqlNativePassword string) bool {