[PATCH] HTTP/2: fixed buffer management with HTTP/2 auto-detection

[Sergey Kandaurov]

# HG changeset patch
# User Sergey Kandaurov <pluknet at nginx.com>
# Date 1697808142 -14400
#      Fri Oct 20 17:22:22 2023 +0400
# Node ID 318c8ace6aa24506004bfbb7d52674f61a3716a5
# Parent  3038bd4d78169a5e8a2624d79cf76f45f0805ddc
HTTP/2: fixed buffer management with HTTP/2 auto-detection.

As part of normal HTTP/2 processing, incomplete frames are saved in the
control state using a fixed size memcpy of NGX_HTTP_V2_STATE_BUFFER_SIZE.
For this matter, two state buffers are reserved in the HTTP/2 recv buffer.

As part of HTTP/2 auto-detection on plain TCP connections, initial data
is first read into a buffer specified by the client_header_buffer_size
directive that doesn't have state reservation.  Previously, this made it
possible to over-read the buffer as part of saving the state.

The fix is to read the available buffer size rather than a fixed size.
Although memcpy of a fixed size can produce a better optimized code,
handling of incomplete frames isn't a common execution path, so it was
sacrificed for the sake of simplicity of the fix.

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -386,13 +386,11 @@ ngx_http_v2_read_handler(ngx_event_t *re
     h2mcf = ngx_http_get_module_main_conf(h2c->http_connection->conf_ctx,
                                           ngx_http_v2_module);
 
-    available = h2mcf->recv_buffer_size - 2 * NGX_HTTP_V2_STATE_BUFFER_SIZE;
+    available = h2mcf->recv_buffer_size - NGX_HTTP_V2_STATE_BUFFER_SIZE;
 
     do {
         p = h2mcf->recv_buffer;
-
-        ngx_memcpy(p, h2c->state.buffer, NGX_HTTP_V2_STATE_BUFFER_SIZE);
-        end = p + h2c->state.buffer_used;
+        end = ngx_cpymem(p, h2c->state.buffer, h2c->state.buffer_used);
 
         n = c->recv(c, end, available);
 
@@ -2592,7 +2590,7 @@ ngx_http_v2_state_save(ngx_http_v2_conne
         return ngx_http_v2_connection_error(h2c, NGX_HTTP_V2_INTERNAL_ERROR);
     }
 
-    ngx_memcpy(h2c->state.buffer, pos, NGX_HTTP_V2_STATE_BUFFER_SIZE);
+    ngx_memcpy(h2c->state.buffer, pos, size);
 
     h2c->state.buffer_used = size;
     h2c->state.handler = handler;
diff --git a/src/http/v2/ngx_http_v2_module.c b/src/http/v2/ngx_http_v2_module.c
--- a/src/http/v2/ngx_http_v2_module.c
+++ b/src/http/v2/ngx_http_v2_module.c
@@ -388,7 +388,7 @@ ngx_http_v2_recv_buffer_size(ngx_conf_t 
 {
     size_t *sp = data;
 
-    if (*sp <= 2 * NGX_HTTP_V2_STATE_BUFFER_SIZE) {
+    if (*sp <= NGX_HTTP_V2_STATE_BUFFER_SIZE) {
         return "value is too small";
     }