nginx: Mitigate HTTP/2 Stream Resets Flood impact

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 <jasper@fancydomain.eu>
Signed-off-by: Armin Kuster <akuster808@gmail.com>

3 files changed, 95 insertions, 0 deletions

diff --git a/meta-webserver/recipes-httpd/nginx/files/0001-HTTP-2-per-iteration-stream-handling-limit.patch b/meta-webserver/recipes-httpd/nginx/files/0001-HTTP-2-per-iteration-stream-handling-limit.patch
new file mode 100644
index 0000000000..7dd1e721c0
--- /dev/null
+++ b/meta-webserver/recipes-httpd/nginx/files/0001-HTTP-2-per-iteration-stream-handling-limit.patch
@@ -0,0 +1,92 @@
+From 2b9667f36551406169e3e2a6a774466ac70a83c0 Mon Sep 17 00:00:00 2001
+From: Maxim Dounin <mdounin@mdounin.ru>
+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 <jasper@fancydomain.eu>
+---
+ 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
+
diff --git a/meta-webserver/recipes-httpd/nginx/nginx_1.16.1.bb b/meta-webserver/recipes-httpd/nginx/nginx_1.16.1.bb
index 07e9f6ddbc..39cfd3a67b 100644
--- a/meta-webserver/recipes-httpd/nginx/nginx_1.16.1.bb
+++ b/meta-webserver/recipes-httpd/nginx/nginx_1.16.1.bb
@@ -7,4 +7,5 @@ SRC_URI[sha256sum] = "f11c2a6dd1d3515736f0324857957db2de98be862461b5a542a3ac6188
 
 SRC_URI += "file://CVE-2019-20372.patch \
             file://CVE-2022-41741-CVE-2022-41742.patch \
+            file://0001-HTTP-2-per-iteration-stream-handling-limit.patch \
            "
diff --git a/meta-webserver/recipes-httpd/nginx/nginx_1.17.8.bb b/meta-webserver/recipes-httpd/nginx/nginx_1.17.8.bb
index 3d2a5edd26..9fd6d73428 100644
--- a/meta-webserver/recipes-httpd/nginx/nginx_1.17.8.bb
+++ b/meta-webserver/recipes-httpd/nginx/nginx_1.17.8.bb
@@ -8,3 +8,5 @@ LIC_FILES_CHKSUM = "file://LICENSE;md5=52e384aaac868b755b93ad5535e2d075"
 
 SRC_URI[md5sum] = "29cd861a13aae69a058cbabaae86177b"
 SRC_URI[sha256sum] = "97d23ecf6d5150b30e284b40e8a6f7e3bb5be6b601e373a4d013768d5a25965b"
+
+SRC_URI += "file://0001-HTTP-2-per-iteration-stream-handling-limit.patch"