Upstream error handling issue

Maxim Dounin mdounin at
Mon Aug 19 15:17:45 UTC 2013


On Mon, Aug 19, 2013 at 05:17:24PM +0300, Aviram Cohen wrote:

> Hello!
> I have encountered a potential bug in Nginx's upstream module -
> When the upstream server is an SSL server, if an error occurs in
> ngx_http_upstream_ssl_handshake() - the
> function ngx_http_run_posted_requests() is never called.
> This happens when initiating an SSL connection, the SSL module handles the
> handshake, and not the upstream module (meaning ngx_http_upstream_handler()
> is not involved in the process), and so if an error occurs, there's no one
> who calls ngx_http_run_posted_requests().
> The effect of this issue is the requests that "spawn" subrequests that use
> the upstream error get stuck in case of an SSL error.
> I can suggest two possible fixes (in the file ngx_http_upstream.c):
>   - Add a call to ngx_http_run_posted_requests() to the end
> of ngx_http_upstream_finalize_request().
>   - Add a call to ngx_http_run_posted_requests() after calling
> ngx_http_upstream_finalize_request() during error handling of the SSL
> connection establishment.
> Can anyone verify this issue and the suggested solution? If so, I'll be
> more than happy to submit a patch.

Yes, it looks like there is a problem.

The ngx_http_run_posted_requests() is usually called by an event 
handler, so adding a call to ngx_http_upstream_ssl_handshake() 
might be more appropriate.  Something like this should fix the 

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
@@ -1343,8 +1343,11 @@ ngx_http_upstream_ssl_handshake(ngx_conn
+    c = r->connection;
     ngx_http_upstream_next(r, u, NGX_HTTP_UPSTREAM_FT_ERROR);
+    ngx_http_run_posted_requests(c);

Maxim Dounin

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