BUG/MEDIUM: quic: 0-RTT securing

It has been reported by Wedl Michael, a student at the University of Applied
Sciences St. Poelten, a potential vulnerability into haproxy as described below.

An attacker could have obtained a TLS session ticket after having established
a connection to an haproxy QUIC listener, using its real IP address. The
attacker has not even to send a application level request (HTTP3). Then
the attacker could open a 0-RTT session with a spoofed IP address
trusted by the QUIC listen to bypass IP allow/block list and send HTTP3 requests.

To mitigate this vulnerability, one decided to use a token which can be provided
to the client each time it successfully managed to connect to haproxy. These
tokens may be reused for future connections to validate the address/path of the
remote peer as this is done with the Retry token which is used for the current
connection, not the next one. Such tokens are transported by NEW_TOKEN frames
which was not used at this time by haproxy.

So, each time a client connect to an haproxy QUIC listener with 0-RTT
enabled, it is provided with such a token which can be reused for the
next 0-RTT session. If no such a token is presented by the client,
haproxy checks if the session is a 0-RTT one, so with early-data presented
by the client. Contrary to the Retry token, the decision to refuse the
connection is made only when the TLS stack has been provided with
enough early-data from the Initial ClientHello TLS message and when
these data have been accepted. Hopefully, this event arrives fast enough
to allow haproxy to kill the connection if some early-data have been accepted
without token presented by the client.

quic_build_post_handshake_frames() has been modified to build a NEW_TOKEN
frame with this newly implemented token to be transported inside.

quic_tls_derive_retry_token_secret() was renamed to quic_do_tls_derive_token_secre()
and modified to be reused and derive the secret for the new token implementation.

quic_token_validate() has been implemented to validate both the Retry and
the new token implemented by this patch. When this is a non-retry token
which could not be validated, the datagram received is marked as requiring
a Retry packet to be sent, and no connection is created.

When the Initial packet does not embed any non-retry token and if 0-RTT is enabled
the connection is marked with this new flag: QUIC_FL_CONN_NO_TOKEN_RCVD. As soon
as the TLS stack detects that some early-data have been provided and accepted by
the client, the connection is marked to be killed (QUIC_FL_CONN_TO_KILL) from
ha_quic_add_handshake_data(). This is done calling qc_ssl_eary_data_accepted()
new function. The secret TLS handshake is interrupted as soon as possible returnin
0 from ha_quic_add_handshake_data(). The connection is also marked as
requiring a Retry packet to be sent (QUIC_FL_CONN_SEND_RETRY) from
ha_quic_add_handshake_data(). The the handshake I/O handler (quic_conn_io_cb())
knows how to behave: kill the connection after having sent a Retry packet.

About TLS stack compatibility, this patch is supported by aws-lc. It is
disabled for wolfssl which does not support 0-RTT at this time thanks
to HAVE_SSL_0RTT_QUIC.

This patch depends on these commits:

     MINOR: quic: Add trace for QUIC_EV_CONN_IO_CB event.
     MINOR: quic: Implement qc_ssl_eary_data_accepted().
     MINOR: quic: Modify NEW_TOKEN frame structure (qf_new_token struct)
     BUG/MINOR: quic: Missing incrementation in NEW_TOKEN frame builder
     MINOR: quic: Token for future connections implementation.
     MINOR: quic: Implement quic_tls_derive_token_secret().
     MINOR: tools: Implement ipaddrcpy().

Must be backported as far as 2.6.

include/haproxy/quic_conn-t.h

@@ -445,6 +445,8 @@ struct quic_conn_closed {
 #define QUIC_FL_CONN_IPKTNS_DCD                  (1U << 15) /* Initial packet number space discarded  */
 #define QUIC_FL_CONN_HPKTNS_DCD                  (1U << 16) /* Handshake packet number space discarded  */
 #define QUIC_FL_CONN_PEER_VALIDATED_ADDR         (1U << 17) /* Peer address is considered as validated for this connection. */
+#define QUIC_FL_CONN_NO_TOKEN_RCVD               (1U << 18) /* Client dit not send any token */
+#define QUIC_FL_CONN_SEND_RETRY                  (1U << 19) /* A send retry packet must be sent */
 /* gap here */
 #define QUIC_FL_CONN_TO_KILL                     (1U << 24) /* Unusable connection, to be killed */
 #define QUIC_FL_CONN_TX_TP_RECEIVED              (1U << 25) /* Peer transport parameters have been received (used for the transmitting part) */

src/quic_conn.c

@@ -57,6 +57,7 @@
 #include <haproxy/quic_sock.h>
 #include <haproxy/quic_stats.h>
 #include <haproxy/quic_stream.h>
+#include <haproxy/quic_token.h>
 #include <haproxy/quic_tp.h>
 #include <haproxy/quic_trace.h>
 #include <haproxy/quic_tx.h>
@@ -479,6 +480,30 @@ int quic_build_post_handshake_frames(struct quic_conn *qc)
 		}
 
 		LIST_APPEND(&frm_list, &frm->list);
+
+#ifdef HAVE_SSL_0RTT_QUIC
+		if (qc->li->bind_conf->ssl_conf.early_data) {
+			size_t new_token_frm_len;
+
+			frm = qc_frm_alloc(QUIC_FT_NEW_TOKEN);
+			if (!frm) {
+				TRACE_ERROR("frame allocation error", QUIC_EV_CONN_IO_CB, qc);
+				goto leave;
+			}
+
+			new_token_frm_len =
+				quic_generate_token(frm->new_token.data,
+				                    sizeof(frm->new_token.data), &qc->peer_addr);
+			if (!new_token_frm_len) {
+				TRACE_ERROR("token generation failed", QUIC_EV_CONN_IO_CB, qc);
+				goto leave;
+			}
+
+			BUG_ON(new_token_frm_len != sizeof(frm->new_token.data));
+			frm->new_token.len = new_token_frm_len;
+			LIST_APPEND(&frm_list, &frm->list);
+		}
+#endif
 	}
 
 	/* Initialize <max> connection IDs minus one: there is
@@ -761,6 +786,11 @@ struct task *quic_conn_io_cb(struct task *t, void *context, unsigned int state)
 		HA_ATOMIC_AND(&tl->state, ~TASK_HEAVY);
 	}
 
+	if (qc->flags & QUIC_FL_CONN_TO_KILL) {
+		TRACE_DEVEL("connection to be killed", QUIC_EV_CONN_PHPKTS, qc);
+		goto out;
+	}
+
 	/* Retranmissions */
 	if (qc->flags & QUIC_FL_CONN_RETRANS_NEEDED) {
 		TRACE_DEVEL("retransmission needed", QUIC_EV_CONN_PHPKTS, qc);
@@ -862,7 +892,25 @@ struct task *quic_conn_io_cb(struct task *t, void *context, unsigned int state)
 		quic_nictx_free(qc);
 	}
 
-	if ((qc->flags & QUIC_FL_CONN_CLOSING) && qc->mux_state != QC_MUX_READY) {
+	if (qc->flags & QUIC_FL_CONN_SEND_RETRY) {
+		struct quic_counters *prx_counters;
+		struct proxy *prx = qc->li->bind_conf->frontend;
+		struct quic_rx_packet pkt = {
+			.scid = qc->dcid,
+			.dcid = qc->odcid,
+		};
+
+		prx_counters = EXTRA_COUNTERS_GET(prx->extra_counters_fe, &quic_stats_module);
+		if (send_retry(qc->li->rx.fd, &qc->peer_addr, &pkt, qc->original_version)) {
+			TRACE_ERROR("Error during Retry generation",
+			            QUIC_EV_CONN_LPKT, NULL, NULL, NULL, qc->original_version);
+		}
+		else
+			HA_ATOMIC_INC(&prx_counters->retry_sent);
+	}
+
+	if ((qc->flags & (QUIC_FL_CONN_CLOSING|QUIC_FL_CONN_TO_KILL)) &&
+	    qc->mux_state != QC_MUX_READY) {
 		quic_conn_release(qc);
 		qc = NULL;
 	}
@@ -969,11 +1017,15 @@ struct task *qc_process_timer(struct task *task, void *ctx, unsigned int state)
  * for QUIC servers (or haproxy listeners).
  * <dcid> is the destination connection ID, <scid> is the source connection ID.
  * This latter <scid> CID as the same value on the wire as the one for <conn_id>
- * which is the first CID of this connection but a different internal representation used to build
+ * which is the first CID of this connection but a different internal
+ * representation used to build
  * NEW_CONNECTION_ID frames. This is the responsibility of the caller to insert
  * <conn_id> in the CIDs tree for this connection (qc->cids).
- * <token> is the token found to be used for this connection with <token_len> as
- * length. Endpoints addresses are specified via <local_addr> and <peer_addr>.
+ * <token> is a boolean denoting if a token was received for this connection
+ * from an Initial packet.
+ * <token_odcid> is the original destination connection ID which was embedded
+ * into the Retry token sent to the client before instantiated this connection.
+ * Endpoints addresses are specified via <local_addr> and <peer_addr>.
  * Returns the connection if succeeded, NULL if not.
  */
 struct quic_conn *qc_new_conn(const struct quic_version *qv, int ipv4,
@@ -1080,6 +1132,9 @@ struct quic_conn *qc_new_conn(const struct quic_version *qv, int ipv4,
 		qc->prx_counters = EXTRA_COUNTERS_GET(prx->extra_counters_fe,
 		                                      &quic_stats_module);
 		qc->flags = QUIC_FL_CONN_LISTENER;
+		/* Mark this connection as having not received any token when 0-RTT is enabled. */
+		if (l->bind_conf->ssl_conf.early_data && !token)
+			qc->flags |= QUIC_FL_CONN_NO_TOKEN_RCVD;
 		qc->state = QUIC_HS_ST_SERVER_INITIAL;
 		/* Copy the client original DCID. */
 		qc->odcid = *dcid;
@@ -1102,7 +1157,7 @@ struct quic_conn *qc_new_conn(const struct quic_version *qv, int ipv4,
 	/* If connection is instantiated due to an INITIAL packet with an
 	 * already checked token, consider the peer address as validated.
 	 */
-	if (token_odcid->len) {
+	if (token) {
 		TRACE_STATE("validate peer address due to initial token",
 		            QUIC_EV_CONN_INIT, qc);
 		qc->flags |= QUIC_FL_CONN_PEER_VALIDATED_ADDR;

src/quic_retry.c

@@ -258,17 +258,11 @@ int quic_retry_token_check(struct quic_rx_packet *pkt,
 	TRACE_ENTER(QUIC_EV_CONN_LPKT, qc);
 
 	/* The caller must ensure this. */
-	BUG_ON(!pkt->token_len);
+	BUG_ON(!pkt->token_len || *pkt->token != QUIC_TOKEN_FMT_RETRY);
 
 	prx = l->bind_conf->frontend;
 	prx_counters = EXTRA_COUNTERS_GET(prx->extra_counters_fe, &quic_stats_module);
 
-	if (*pkt->token != QUIC_TOKEN_FMT_RETRY) {
-		/* TODO: New token check */
-		TRACE_PROTO("Packet dropped", QUIC_EV_CONN_LPKT, qc, NULL, NULL, pkt->version);
-		goto leave;
-	}
-
 	if (sizeof buf < tokenlen) {
 		TRACE_ERROR("too short buffer", QUIC_EV_CONN_LPKT, qc);
 		goto err;

src/quic_rx.c

@@ -27,6 +27,7 @@
 #include <haproxy/quic_stream.h>
 #include <haproxy/quic_ssl.h>
 #include <haproxy/quic_tls.h>
+#include <haproxy/quic_token.h>
 #include <haproxy/quic_trace.h>
 #include <haproxy/quic_tx.h>
 #include <haproxy/ssl_sock.h>
@@ -1522,6 +1523,47 @@ static inline int quic_padding_check(const unsigned char *pos,
 	return pos == end;
 }
 
+/* Validate the token, retry or not (provided by NEW_TOKEN) parsed into
+ * <pkt> RX packet from <dgram> datagram.
+ * Return 1 if succeded, 0 if not.
+ */
+static inline int quic_token_validate(struct quic_rx_packet *pkt,
+                                      struct quic_dgram *dgram,
+                                      struct listener *l, struct quic_conn *qc,
+                                      struct quic_cid *odcid)
+{
+	int ret = 0;
+
+	TRACE_ENTER(QUIC_EV_CONN_LPKT, qc);
+
+	switch (*pkt->token) {
+	case QUIC_TOKEN_FMT_RETRY:
+		ret = quic_retry_token_check(pkt, dgram, l, qc, odcid);
+		break;
+	case QUIC_TOKEN_FMT_NEW:
+		ret = quic_token_check(pkt, dgram, qc);
+		if (!ret) {
+			/* Fallback to a retry token in case of any error. */
+			dgram->flags |= QUIC_DGRAM_FL_SEND_RETRY;
+		}
+		break;
+	default:
+		TRACE_PROTO("Packet dropped", QUIC_EV_CONN_LPKT, qc, NULL, NULL, pkt->version);
+		break;
+	}
+
+	if (!ret)
+		goto err;
+
+	ret = 1;
+ leave:
+	TRACE_LEAVE(QUIC_EV_CONN_LPKT, qc);
+	return ret;
+ err:
+	TRACE_DEVEL("leaving in error", QUIC_EV_CONN_LPKT, qc);
+	goto leave;
+}
+
 /* Find the associated connection to the packet <pkt> or create a new one if
  * this is an Initial packet. <dgram> is the datagram containing the packet and
  * <l> is the listener instance on which it was received.
@@ -1581,9 +1623,25 @@ static struct quic_conn *quic_rx_pkt_retrieve_conn(struct quic_rx_packet *pkt,
 			}
 
 			if (pkt->token_len) {
-				/* Validate the token only when connection is unknown. */
-				if (!quic_retry_token_check(pkt, dgram, l, qc, &token_odcid))
+				TRACE_PROTO("Initial with token", QUIC_EV_CONN_LPKT, NULL, NULL, NULL, pkt->version);
+				/* Validate the token, retry or not only when connection is unknown. */
+				if (!quic_token_validate(pkt, dgram, l, qc, &token_odcid)) {
+					if (dgram->flags & QUIC_DGRAM_FL_SEND_RETRY) {
+						if (send_retry(l->rx.fd, &dgram->saddr, pkt, pkt->version)) {
+							TRACE_ERROR("Error during Retry generation",
+							            QUIC_EV_CONN_LPKT, NULL, NULL, NULL, pkt->version);
+						}
+						else
+							HA_ATOMIC_INC(&prx_counters->retry_sent);
+
+						goto out;
+					}
+
 					goto err;
+				}
+			}
+			else {
+				TRACE_PROTO("Initial without token", QUIC_EV_CONN_LPKT, NULL, NULL, NULL, pkt->version);
 			}
 
 			if (!quic_init_exec_rules(l, dgram)) {

src/quic_ssl.c

@@ -353,6 +353,23 @@ static int ha_quic_add_handshake_data(SSL *ssl, enum ssl_encryption_level_t leve
 
 	TRACE_ENTER(QUIC_EV_CONN_ADDDATA, qc);
 
+	TRACE_PROTO("ha_quic_add_handshake_data() called", QUIC_EV_CONN_IO_CB, qc, NULL, ssl);
+
+#ifdef HAVE_SSL_0RTT_QUIC
+	/* Detect asap if some 0-RTT data were accepted for this connection.
+	 * If this is the case and no token was provided, interrupt the useless
+	 * secrets derivations. A Retry packet must be sent, and this connection
+	 * must be killed.
+	 * Note that QUIC_FL_CONN_NO_TOKEN_RCVD is possibly set only for when 0-RTT is
+	 * enabled for the connection.
+	 */
+	if ((qc->flags & QUIC_FL_CONN_NO_TOKEN_RCVD) && qc_ssl_eary_data_accepted(ssl)) {
+		TRACE_PROTO("connection to be killed", QUIC_EV_CONN_ADDDATA, qc);
+		qc->flags |= QUIC_FL_CONN_TO_KILL|QUIC_FL_CONN_SEND_RETRY;
+		goto leave;
+	}
+#endif
+
 	if (qc->flags & QUIC_FL_CONN_TO_KILL) {
 		TRACE_PROTO("connection to be killed", QUIC_EV_CONN_ADDDATA, qc);
 		goto out;
@@ -533,9 +550,10 @@ static int qc_ssl_provide_quic_data(struct ncbuf *ncbuf,
 	state = qc->state;
 	if (state < QUIC_HS_ST_COMPLETE) {
 		ssl_err = SSL_do_handshake(ctx->ssl);
+		TRACE_PROTO("SSL_do_handshake() called", QUIC_EV_CONN_IO_CB, qc, NULL, ctx->ssl);
 
 		if (qc->flags & QUIC_FL_CONN_TO_KILL) {
-			TRACE_DEVEL("connection to be killed", QUIC_EV_CONN_IO_CB, qc);
+			TRACE_DEVEL("connection to be killed", QUIC_EV_CONN_IO_CB, qc, &state, ctx->ssl);
 			goto leave;
 		}