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Subject [Bug 54526] New: mod_proxy_http ignores request abortion
Date Tue, 05 Feb 2013 14:37:31 GMT

            Bug ID: 54526
           Summary: mod_proxy_http ignores request abortion
           Product: Apache httpd-2
           Version: 2.4.3
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: mod_proxy_http
    Classification: Unclassified

our application is affected by "Double Execution of onload and
onreadystatechange Events for Script Elements" bug in IE9. See

It means when IE9 loads one HTML page twice. First hit is aborted when the
second occures.
There are CSS, JS and images on that page. Sometimes they started being served
as part of first hit but the request is aborted almost immediatelly.

Our application is behind reverse proxy. All traffic is thru HTTPS.

The problem is that sometimes the reverse proxy keeps established connection to
backend until the backend times out.

Log from reverse proxy: - - [01/Feb/2013:14:01:15 +0000] "GET /main.css HTTP/1.1" 200 - - - [01/Feb/2013:14:01:15 +0000] "GET /main.css HTTP/1.1" 200

Log from application: - - [01/Feb/2013:14:01:15 +0000] "GET /main.css HTTP/1.1" 200
9376 300100937 - - [01/Feb/2013:14:01:15 +0000] "GET /main.css HTTP/1.1" 200
9376 12003
The last number is %D - The time taken to serve the request, in microseconds.

I was trying to reproduce this behavior but the time window to trigger the bug
is too small.

We have enabled mod_deflate recently and the log has changed.
Now it reports it sent 26 bytes to client during such aborted request. The
problem with established connection to backend persist.

I can see code in mod_proxy_http like:
if (ap_pass_brigade(r->output_filters, bb) || c->aborted)
but I'm not sure where in the code the "aborted" field is supposed to be set.

In similar code in mod_proxy_connect is the c->aborted check before
That would mean that right code is:
if (c->aborted || ap_pass_brigade(r->output_filters, bb))

My main concern is that somebody who knows exact timing to trigger the bug can
DoS us.

Any hints?

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