QUIC: fixed handling of RETIRE_CONNECTION_ID frame.

Previously, the retired socket was not closed if it didn't match
active or backup.

New sockets could not be created (due to count limit), since retired socket
was not closed before calling ngx_quic_create_sockets().

When replacing retired socket, new socket is only requested after closing
old one, to avoid hitting the limit on the number of active connection ids.

Together with added restrictions, this fixes an issue when a current socket
could be closed during migration, recreated and erroneously reused leading
to null pointer dereference.

3 files changed, 55 insertions, 30 deletions

diff --git a/src/event/quic/ngx_event_quic_connid.c b/src/event/quic/ngx_event_quic_connid.c
index 8b9805b1e..503a71b4e 100644
--- a/src/event/quic/ngx_event_quic_connid.c
+++ b/src/event/quic/ngx_event_quic_connid.c
@@ -403,6 +403,10 @@ ngx_quic_handle_retire_connection_id_frame(ngx_connection_t *c,
         return NGX_OK;
     }
 
+    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic socket #%uL is retired", qsock->sid.seqnum);
+
+    /* check if client is willing to retire sid we have in use */
     if (qsock->sid.seqnum == qc->socket->sid.seqnum) {
         tmp = &qc->socket;
 
@@ -410,46 +414,68 @@ ngx_quic_handle_retire_connection_id_frame(ngx_connection_t *c,
         tmp = &qc->backup;
 
     } else {
-        tmp = NULL;
-    }
-
-    if (ngx_quic_create_sockets(c) != NGX_OK) {
-        return NGX_ERROR;
-    }
 
-    if (tmp) {
-        /* replace socket in use (active or backup) */
+        ngx_quic_close_socket(c, qsock);
 
-        ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                       "quic %s socket #%uL:%uL:%uL retired",
-                       (*tmp) == qc->socket ? "active" : "backup",
-                       (*tmp)->sid.seqnum, (*tmp)->cid->seqnum,
-                       (*tmp)->path->seqnum);
-
-        qsock = ngx_quic_get_unconnected_socket(c);
-        if (qsock == NULL) {
+        /* restore socket count up to a limit after deletion */
+        if (ngx_quic_create_sockets(c) != NGX_OK) {
             return NGX_ERROR;
         }
 
-        path = (*tmp)->path;
-        cid = (*tmp)->cid;
+        return NGX_OK;
+    }
 
-        ngx_quic_connect(c, qsock, path, cid);
+    /* preserve path/cid from retired socket */
+    path = qsock->path;
+    cid = qsock->cid;
 
+    /* ensure that closing_socket will not drop path and cid */
+    path->refcnt++;
+    cid->refcnt++;
 
-        ngx_log_debug5(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                       "quic %s socket is now #%uL:%uL:%uL (%s)",
-                       (*tmp) == qc->socket ? "active" : "backup",
-                       qsock->sid.seqnum, qsock->cid->seqnum,
-                       qsock->path->seqnum,
-                       ngx_quic_path_state_str(qsock->path));
+    ngx_quic_close_socket(c, qsock);
 
-        ngx_quic_close_socket(c, *tmp); /* no longer used */
+    /* restore original values */
+    path->refcnt--;
+    cid->refcnt--;
 
-        *tmp = qsock;
+    /* restore socket count up to a limit after deletion */
+    if (ngx_quic_create_sockets(c) != NGX_OK) {
+        goto failed;
     }
 
+    qsock = ngx_quic_get_unconnected_socket(c);
+    if (qsock == NULL) {
+        qc->error = NGX_QUIC_ERR_CONNECTION_ID_LIMIT_ERROR;
+        qc->error_reason = "not enough server IDs";
+        goto failed;
+    }
+
+    ngx_quic_connect(c, qsock, path, cid);
+
+    ngx_log_debug5(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic %s socket is now #%uL:%uL:%uL (%s)",
+                   (*tmp) == qc->socket ? "active" : "backup",
+                   qsock->sid.seqnum, qsock->cid->seqnum,
+                   qsock->path->seqnum,
+                   ngx_quic_path_state_str(qsock->path));
+
+    /* restore active/backup pointer in quic connection */
+    *tmp = qsock;
+
     return NGX_OK;
+
+failed:
+
+    /*
+     * socket was closed, path and cid were preserved artifically
+     * to be reused, but it didn't happen, thus unref here
+     */
+
+    ngx_quic_unref_path(c, path);
+    ngx_quic_unref_client_id(c, cid);
+
+    return NGX_ERROR;
 }
 
 
diff --git a/src/event/quic/ngx_event_quic_socket.c b/src/event/quic/ngx_event_quic_socket.c
index ddde68f09..3b507fca8 100644
--- a/src/event/quic/ngx_event_quic_socket.c
+++ b/src/event/quic/ngx_event_quic_socket.c
@@ -14,8 +14,6 @@ static ngx_int_t ngx_quic_create_temp_socket(ngx_connection_t *c,
     ngx_quic_connection_t *qc, ngx_str_t *dcid, ngx_quic_path_t *path,
     ngx_quic_client_id_t *cid);
 
-static void ngx_quic_unref_path(ngx_connection_t *c, ngx_quic_path_t *path);
-
 
 ngx_int_t
 ngx_quic_open_sockets(ngx_connection_t *c, ngx_quic_connection_t *qc,
@@ -207,7 +205,7 @@ ngx_quic_close_socket(ngx_connection_t *c, ngx_quic_socket_t *qsock)
 }
 
 
-static void
+void
 ngx_quic_unref_path(ngx_connection_t *c, ngx_quic_path_t *path)
 {
     ngx_quic_connection_t  *qc;
diff --git a/src/event/quic/ngx_event_quic_socket.h b/src/event/quic/ngx_event_quic_socket.h
index 1372822c0..72ed67ad0 100644
--- a/src/event/quic/ngx_event_quic_socket.h
+++ b/src/event/quic/ngx_event_quic_socket.h
@@ -22,6 +22,7 @@ ngx_int_t ngx_quic_listen(ngx_connection_t *c, ngx_quic_connection_t *qc,
     ngx_quic_socket_t *qsock);
 void ngx_quic_close_socket(ngx_connection_t *c, ngx_quic_socket_t *qsock);
 
+void ngx_quic_unref_path(ngx_connection_t *c, ngx_quic_path_t *path);
 void ngx_quic_connect(ngx_connection_t *c, ngx_quic_socket_t *qsock,
     ngx_quic_path_t *path, ngx_quic_client_id_t *cid);