# HG changeset patch
# User Ruslan Ermilov <ru@nginx.com>
# Date 1541510989 -10800
# Node ID e7f19d268c72db6908cc467fbba9df402c3389b8
# Parent  d4448892a2943f27e5360705c719bfd045c8ef26
HTTP/2: limit the number of idle state switches.

An attack that continuously switches HTTP/2 connection between
idle and active states can result in excessive CPU usage.
This is because when a connection switches to the idle state,
all of its memory pool caches are freed.

This change limits the maximum allowed number of idle state
switches to 10 * http2_max_requests (i.e., 10000 by default).
This limits possible CPU usage in one connection, and also
imposes a limit on the maximum lifetime of a connection.

Initially reported by Gal Goldshtein from F5 Networks.

diff -r d4448892a294 -r e7f19d268c72 src/http/v2/ngx_http_v2.h
--- a/src/http/v2/ngx_http_v2.h	Tue Nov 06 16:29:35 2018 +0300
+++ b/src/http/v2/ngx_http_v2.h	Tue Nov 06 16:29:49 2018 +0300
@@ -121,6 +121,7 @@
 
     ngx_uint_t                       processing;
     ngx_uint_t                       frames;
+    ngx_uint_t                       idle;
 
     size_t                           send_window;
     size_t                           recv_window;