QUIC: reworked migration handling.

The quic connection now holds active, backup and probe paths instead
of sockets.  The number of migration paths is now limited and cannot
be inflated by a bad client or an attacker.

The client id is now associated with path rather than socket. This allows
to simplify processing of output and connection ids handling.

New migration abandons any previously started migrations.  This allows to
free consumed client ids and request new for use in future migrations and
make progress in case when connection id limit is hit during migration.

A path now can be revalidated without losing its state.

The patch also fixes various issues with NAT rebinding case handling:
    - paths are now validated (previously, there was no validation
      and paths were left in limited state)
    - attempt to reuse id on different path is now again verified
      (this was broken in 40445fc7c403)
    - former path is now validated in case of apparent migration

1 files changed, 34 insertions, 32 deletions

diff --git a/src/event/quic/ngx_event_quic.c b/src/event/quic/ngx_event_quic.c
index 96488c6a7..d47d0bc4e 100644
--- a/src/event/quic/ngx_event_quic.c
+++ b/src/event/quic/ngx_event_quic.c
@@ -131,8 +131,8 @@ ngx_quic_apply_transport_params(ngx_connection_t *c, ngx_quic_tp_t *ctp)
 
     qc = ngx_quic_get_connection(c);
 
-    scid.data = qc->socket->cid->id;
-    scid.len = qc->socket->cid->len;
+    scid.data = qc->path->cid->id;
+    scid.len = qc->path->cid->len;
 
     if (scid.len != ctp->initial_scid.len
         || ngx_memcmp(scid.data, ctp->initial_scid.data, scid.len) != 0)
@@ -373,7 +373,7 @@ ngx_quic_handle_stateless_reset(ngx_connection_t *c, ngx_quic_header_t *pkt)
     {
         cid = ngx_queue_data(q, ngx_quic_client_id_t, queue);
 
-        if (cid->seqnum == 0 || cid->refcnt == 0) {
+        if (cid->seqnum == 0 || !cid->used) {
             /*
              * No stateless reset token in initial connection id.
              * Don't accept a token from an unused connection id.
@@ -673,10 +673,12 @@ ngx_quic_handle_datagram(ngx_connection_t *c, ngx_buf_t *b,
     u_char                 *p, *start;
     ngx_int_t               rc;
     ngx_uint_t              good;
+    ngx_quic_path_t        *path;
     ngx_quic_header_t       pkt;
     ngx_quic_connection_t  *qc;
 
     good = 0;
+    path = NULL;
 
     size = b->last - b->pos;
 
@@ -690,6 +692,7 @@ ngx_quic_handle_datagram(ngx_connection_t *c, ngx_buf_t *b,
         pkt.len = b->last - p;
         pkt.log = c->log;
         pkt.first = (p == start) ? 1 : 0;
+        pkt.path = path;
         pkt.flags = p[0];
         pkt.raw->pos++;
 
@@ -720,6 +723,8 @@ ngx_quic_handle_datagram(ngx_connection_t *c, ngx_buf_t *b,
             good = 1;
         }
 
+        path = pkt.path; /* preserve packet path from 1st packet */
+
         /* NGX_OK || NGX_DECLINED */
 
         /*
@@ -825,14 +830,15 @@ ngx_quic_handle_packet(ngx_connection_t *c, ngx_quic_conf_t *conf,
             }
 
             if (pkt->first) {
-                if (ngx_quic_find_path(c, c->udp->dgram->sockaddr,
-                                       c->udp->dgram->socklen)
-                    == NULL)
+                if (ngx_cmp_sockaddr(c->udp->dgram->sockaddr,
+                                     c->udp->dgram->socklen,
+                                     qc->path->sockaddr, qc->path->socklen, 1)
+                    != NGX_OK)
                 {
                     /* packet comes from unknown path, possibly migration */
                     ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0,
                                   "quic too early migration attempt");
-                    return NGX_DECLINED;
+                    return NGX_DONE;
                 }
             }
 
@@ -991,9 +997,12 @@ ngx_quic_handle_payload(ngx_connection_t *c, ngx_quic_header_t *pkt)
 
     pkt->decrypted = 1;
 
-    if (pkt->first) {
-        if (ngx_quic_update_paths(c, pkt) != NGX_OK) {
-            return NGX_ERROR;
+    c->log->action = "handling decrypted packet";
+
+    if (pkt->path == NULL) {
+        rc = ngx_quic_set_path(c, pkt);
+        if (rc != NGX_OK) {
+            return rc;
         }
     }
 
@@ -1012,9 +1021,10 @@ ngx_quic_handle_payload(ngx_connection_t *c, ngx_quic_header_t *pkt)
          */
         ngx_quic_discard_ctx(c, ssl_encryption_initial);
 
-        if (qc->socket->path->state != NGX_QUIC_PATH_VALIDATED) {
-            qc->socket->path->state = NGX_QUIC_PATH_VALIDATED;
-            qc->socket->path->limited = 0;
+        if (!qc->path->validated) {
+            qc->path->validated = 1;
+            qc->path->limited = 0;
+            ngx_quic_path_dbg(c, "in handshake", qc->path);
             ngx_post_event(&qc->push, &ngx_posted_events);
         }
     }
@@ -1153,7 +1163,6 @@ ngx_quic_handle_frames(ngx_connection_t *c, ngx_quic_header_t *pkt)
     ngx_uint_t              do_close, nonprobing;
     ngx_chain_t             chain;
     ngx_quic_frame_t        frame;
-    ngx_quic_socket_t      *qsock;
     ngx_quic_connection_t  *qc;
 
     qc = ngx_quic_get_connection(c);
@@ -1335,7 +1344,8 @@ ngx_quic_handle_frames(ngx_connection_t *c, ngx_quic_header_t *pkt)
 
         case NGX_QUIC_FT_PATH_CHALLENGE:
 
-            if (ngx_quic_handle_path_challenge_frame(c, &frame.u.path_challenge)
+            if (ngx_quic_handle_path_challenge_frame(c, pkt,
+                                                     &frame.u.path_challenge)
                 != NGX_OK)
             {
                 return NGX_ERROR;
@@ -1394,26 +1404,18 @@ ngx_quic_handle_frames(ngx_connection_t *c, ngx_quic_header_t *pkt)
         ngx_quic_close_connection(c, NGX_OK);
     }
 
-    qsock = ngx_quic_get_socket(c);
+    if (pkt->path != qc->path && nonprobing) {
 
-    if (qsock != qc->socket) {
-
-        if (qsock->path != qc->socket->path && nonprobing) {
-            /*
-             * RFC 9000, 9.2.  Initiating Connection Migration
-             *
-             * An endpoint can migrate a connection to a new local
-             * address by sending packets containing non-probing frames
-             * from that address.
-             */
-            if (ngx_quic_handle_migration(c, pkt) != NGX_OK) {
-                return NGX_ERROR;
-            }
-        }
         /*
-         * else: packet arrived via non-default socket;
-         *       no reason to change active path
+         * RFC 9000, 9.2.  Initiating Connection Migration
+         *
+         * An endpoint can migrate a connection to a new local
+         * address by sending packets containing non-probing frames
+         * from that address.
          */
+        if (ngx_quic_handle_migration(c, pkt) != NGX_OK) {
+            return NGX_ERROR;
+        }
     }
 
     if (ngx_quic_ack_packet(c, pkt) != NGX_OK) {