[PATCH] HTTP/2: fixed closed_nodes overflow (ticket #1708)

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1643772371 -10800
#      Wed Feb 02 06:26:11 2022 +0300
# Node ID 0b272d5fd6bd0dcca6dcca8f27f8fcde33119159
# Parent  dd718d1cef3c2ca2754a21176be3318b00be9e62
HTTP/2: fixed closed_nodes overflow (ticket #1708).

With large http2_max_concurrent_streams or http2_max_concurrent_pushes, more
than 255 ngx_http_v2_node_t structures might be allocated, eventually leading
to h2c->closed_nodes overflow when closing corresponding streams.  This will
in turn result in additional allocations in ngx_http_v2_get_node_by_id().

While mostly harmless, it can result in excessive memory usage by a HTTP/2
connection, notably in configurations with many keepalive_requests allowed.
Fix is to use ngx_uint_t for h2c->closed_nodes instead of unsigned:8.

diff --git a/src/http/v2/ngx_http_v2.h b/src/http/v2/ngx_http_v2.h
--- a/src/http/v2/ngx_http_v2.h
+++ b/src/http/v2/ngx_http_v2.h
@@ -153,12 +153,12 @@ struct ngx_http_v2_connection_s {
     ngx_queue_t                      dependencies;
     ngx_queue_t                      closed;
 
+    ngx_uint_t                       closed_nodes;
     ngx_uint_t                       last_sid;
     ngx_uint_t                       last_push;
 
     time_t                           lingering_time;
 
-    unsigned                         closed_nodes:8;
     unsigned                         settings_ack:1;
     unsigned                         table_update:1;
     unsigned                         blocked:1;