[nginx] Upstream: read handler cleared on upstream finalization.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/5850fed24639
branches:  
changeset: 6909:5850fed24639
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Fri Feb 10 20:24:26 2017 +0300
description:
Upstream: read handler cleared on upstream finalization.

With "proxy_ignore_client_abort off" (the default), upstream module changes
r->read_event_handler to ngx_http_upstream_rd_check_broken_connection().
If the handler is not cleared during upstream finalization, it can be
triggered later, causing unexpected effects, if, for example, a request
was redirected to a different location using error_page or X-Accel-Redirect.
In particular, it makes "proxy_ignore_client_abort on" non-working after
a redirection in a configuration like this:

    location = / {
        error_page 502 = /error;
        proxy_pass http://127.0.0.1:8082;
    }

    location /error {
        proxy_pass http://127.0.0.1:8083;
        proxy_ignore_client_abort on;
    }

It is also known to cause segmentation faults with aio used, see
http://mailman.nginx.org/pipermail/nginx-ru/2015-August/056570.html.

Fix is to explicitly set r->read_event_handler to ngx_http_block_reading()
during upstream finalization, similar to how it is done in the request body
reading code and in the limit_req module.

diffstat:

 src/http/ngx_http_upstream.c |  2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diffs (12 lines):

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -4366,6 +4366,8 @@ ngx_http_upstream_finalize_request(ngx_h
         u->buffer.last = u->buffer.pos;
     }
 
+    r->read_event_handler = ngx_http_block_reading;
+
     if (rc == NGX_DECLINED) {
         return;
     }