HTTP/2: enforce writing the sync request body buffer to file. The sync flag of HTTP/2 request body buffer is used when the size of request body is unknown or bigger than configured "client_body_buffer_size". In this case the buffer points to body data inside the global receive buffer that is used for reading all HTTP/2 connections in the worker process. Thus, when the sync flag is set, the buffer must be flushed to a temporary file, otherwise the request body data can be overwritten. Previously, the sync buffer wasn't flushed to a temporary file if the whole body was received in one DATA frame with the END_STREAM flag and wasn't copied into the HTTP/2 body preread buffer. As a result, the request body might be corrupted (ticket #1384). Now, setting r->request_body_in_file_only enforces writing the sync buffer to a temporary file in all cases.

--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -3557,11 +3557,6 @@ ngx_http_v2_read_request_body(ngx_http_r
         rb->buf = ngx_create_temp_buf(r->pool, (size_t) len);
 
     } else {
-        if (stream->preread) {
-            /* enforce writing preread buffer to file */
-            r->request_body_in_file_only = 1;
-        }
-
         rb->buf = ngx_calloc_buf(r->pool);
 
         if (rb->buf != NULL) {
@@ -3660,6 +3655,8 @@ ngx_http_v2_process_request_body(ngx_htt
             buf->pos = buf->start = pos;
             buf->last = buf->end = pos + size;
 
+            r->request_body_in_file_only = 1;
+
         } else {
             if (size > (size_t) (buf->end - buf->last)) {
                 ngx_log_error(NGX_LOG_INFO, fc->log, 0,