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 --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index 8089ddd..9571e71 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -4511,12 +4511,19 @@
#endif
- c->destroyed = 0;
- ngx_reusable_connection(c, 0);
-
h2scf = ngx_http_get_module_srv_conf(h2c->http_connection->conf_ctx,
ngx_http_v2_module);
+ if (h2c->idle++ > 10 * h2scf->max_requests) {
+ ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
+ "http2 flood detected");
+ ngx_http_v2_finalize_connection(h2c, NGX_HTTP_V2_NO_ERROR);
+ return;
+ }
+
+ c->destroyed = 0;
+ ngx_reusable_connection(c, 0);
+
h2c->pool = ngx_create_pool(h2scf->pool_size, h2c->connection->log);
if (h2c->pool == NULL) {
ngx_http_v2_finalize_connection(h2c, NGX_HTTP_V2_INTERNAL_ERROR);
diff --git a/src/http/v2/ngx_http_v2.h b/src/http/v2/ngx_http_v2.h
index e8eaebb..bec2216 100644
--- a/src/http/v2/ngx_http_v2.h
+++ b/src/http/v2/ngx_http_v2.h
@@ -121,6 +121,7 @@
ngx_uint_t processing;
ngx_uint_t frames;
+ ngx_uint_t idle;
ngx_uint_t pushing;
ngx_uint_t concurrent_pushes;