Upstream: fixed X-Accel-Redirect handling from cache files. The X-Accel-Redirect header might appear in cache files if its handling is ignored with the "proxy_ignore_headers" directive. If the cache file is later served with different settings, ngx_http_upstream_process_headers() used to call ngx_http_upstream_finalize_request(NGX_DECLINED), which is not expected to happen before the cleanup handler is installed and resulted in ngx_http_finalize_request(NGX_DONE) (after 5994:5abf5af257a7, nginx 1.7.11), leading to unexpected request counter decrement, "request count is zero" alerts, and segmentation faults. Similarly, errors in ngx_http_upstream_process_headers() resulted in ngx_http_upstream_finalize_request(NGX_HTTP_INTERNAL_SERVER_ERROR) being called. This is also not expected to happen before the cleanup handler is installed, and resulted in ngx_http_finalize_request(NGX_DONE) without proper request finalization. Fix is to avoid calling ngx_http_upstream_finalize_request() from ngx_http_upstream_process_headers(), notably when the cleanup handler is not yet installed. Errors are now simply return NGX_ERROR, so the caller is responsible for proper finalization by calling either ngx_http_finalize_request() or ngx_http_upstream_finalize_request(). And X-Accel-Redirect handling now does not call ngx_http_upstream_finalize_request(NGX_DECLINED) if no cleanup handler is installed. Reported by Jiří Setnička (https://mailman.nginx.org/pipermail/nginx-devel/2024-February/HWLYHOO3DDB3XTFT6X3GRMXIEJ3SJRUA.html).

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>


ngx_queue_t  ngx_posted_accept_events;
ngx_queue_t  ngx_posted_next_events;
ngx_queue_t  ngx_posted_events;


void
ngx_event_process_posted(ngx_cycle_t *cycle, ngx_queue_t *posted)
{
    ngx_queue_t  *q;
    ngx_event_t  *ev;

    while (!ngx_queue_empty(posted)) {

        q = ngx_queue_head(posted);
        ev = ngx_queue_data(q, ngx_event_t, queue);

        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                      "posted event %p", ev);

        ngx_delete_posted_event(ev);

        ev->handler(ev);
    }
}


void
ngx_event_move_posted_next(ngx_cycle_t *cycle)
{
    ngx_queue_t  *q;
    ngx_event_t  *ev;

    for (q = ngx_queue_head(&ngx_posted_next_events);
         q != ngx_queue_sentinel(&ngx_posted_next_events);
         q = ngx_queue_next(q))
    {
        ev = ngx_queue_data(q, ngx_event_t, queue);

        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                      "posted next event %p", ev);

        ev->ready = 1;
        ev->available = -1;
    }

    ngx_queue_add(&ngx_posted_events, &ngx_posted_next_events);
    ngx_queue_init(&ngx_posted_next_events);
}