From 2b9667f36551406169e3e2a6a774466ac70a83c0 Mon Sep 17 00:00:00 2001 From: Maxim Dounin Date: Tue, 10 Oct 2023 15:13:39 +0300 Subject: [PATCH] HTTP/2: per-iteration stream handling limit. To ensure that attempts to flood servers with many streams are detected early, a limit of no more than 2 * max_concurrent_streams new streams per one event loop iteration was introduced. This limit is applied even if max_concurrent_streams is not yet reached - for example, if corresponding streams are handled synchronously or reset. Further, refused streams are now limited to maximum of max_concurrent_streams and 100, similarly to priority_limit initial value, providing some tolerance to clients trying to open several streams at the connection start, yet low tolerance to flooding attempts. Upstream-Status: Backport [https://github.com/nginx/nginx/commit/6ceef192e7af1c507826ac38a2d43f08bf265fb9] Reduces the impact of HTTP/2 Stream Reset flooding in the nginx product (CVE-2023-44487). See: https://www.nginx.com/blog/http-2-rapid-reset-attack-impacting-f5-nginx-products/ This patch only reduces the impact and does not completely mitigate the CVE in question, the latter being due to a design flaw in the HTTP/2 protocol itself. For transparancy reasons I therefore opted to not mark the CVE as resolved, so that integrators can decide for themselves, wheither to enable HTTP/2 support or allow HTTP/1.1 connections only. Signed-off-by: Jasper Orschulko --- src/http/v2/ngx_http_v2.c | 15 +++++++++++++++ src/http/v2/ngx_http_v2.h | 2 ++ 2 files changed, 17 insertions(+) diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c index 3611a2e50..291677aca 100644 --- a/src/http/v2/ngx_http_v2.c +++ b/src/http/v2/ngx_http_v2.c @@ -361,6 +361,7 @@ ngx_http_v2_read_handler(ngx_event_t *rev) ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "http2 read handler"); h2c->blocked = 1; + h2c->new_streams = 0; if (c->close) { c->close = 0; @@ -1320,6 +1321,14 @@ ngx_http_v2_state_headers(ngx_http_v2_connection_t *h2c, u_char *pos, goto rst_stream; } + if (h2c->new_streams++ >= 2 * h2scf->concurrent_streams) { + ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0, + "client sent too many streams at once"); + + status = NGX_HTTP_V2_REFUSED_STREAM; + goto rst_stream; + } + if (!h2c->settings_ack && !(h2c->state.flags & NGX_HTTP_V2_END_STREAM_FLAG) && h2scf->preread_size < NGX_HTTP_V2_DEFAULT_WINDOW) @@ -1385,6 +1394,12 @@ ngx_http_v2_state_headers(ngx_http_v2_connection_t *h2c, u_char *pos, rst_stream: + if (h2c->refused_streams++ > ngx_max(h2scf->concurrent_streams, 100)) { + ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0, + "client sent too many refused streams"); + return ngx_http_v2_connection_error(h2c, NGX_HTTP_V2_NO_ERROR); + } + if (ngx_http_v2_send_rst_stream(h2c, h2c->state.sid, status) != NGX_OK) { return ngx_http_v2_connection_error(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 349229711..6a7aaa62c 100644 --- a/src/http/v2/ngx_http_v2.h +++ b/src/http/v2/ngx_http_v2.h @@ -125,6 +125,8 @@ struct ngx_http_v2_connection_s { ngx_uint_t processing; ngx_uint_t frames; ngx_uint_t idle; + ngx_uint_t new_streams; + ngx_uint_t refused_streams; ngx_uint_t priority_limit; ngx_uint_t pushing; -- 2.42.1