Accessing socket APIs soon after accept

[Quattlebaum, Ryan]

Hi, Adrian. Thanks for taking a look at this.

We're using FreeBSD 8.2 and httpd-2.4.10 with arp-1.5.1 and apr-util-1.5.4.

The problem we're seeing is pretty intermittent, so I hope this test case can                                      shine a little bit of light on the problem. We tried debugging this on our own by adding calls to getsockname() right after the accept call (in srclib/apr/network_io/unix/sockets.c: apr_socket_accept()) and logging the output. That's where we saw invalid data.

I took a look at the source code for the TCP syncache module and the accept syscall. It looks like the new child socket is available for the application to accept after the call to sonewconn returns, but the address information isn't set until further down in the function. Wouldn't this open a window where an application could accept on a socket that the syncache code isn't done configuring?

- Ryan Quattlebaum
________________________________________
From: adrian.chadd at gmail.com <adrian.chadd at gmail.com> on behalf of Adrian Chadd <adrian at freebsd.org>
Sent: Thursday, January 15, 2015 1:20 PM
To: Quattlebaum, Ryan
Cc: freebsd-net at freebsd.org
Subject: Re: Accessing socket APIs soon after accept

On 15 January 2015 at 08:29, Quattlebaum, Ryan
<Ryan.Quattlebaum at netapp.com> wrote:
> Is there anything preventing applications from calling functions e.g. getsockname() right after accept()? Or is there a recommended pattern that applications should use to ensure they get correct data? We recently upgraded to a new version of Apache and are seeing uninitialized data coming back from a few of these calls.

I'm under the impression that once you get the FD from accept(), it
should be fully formed and ready.

Which version of FreeBSD/apache is it? can you come up with a test
case that shows that it's happening?



-adrian

> Thanks,
>
> Ryan Quattlebaum
> Software Developer, NetApp, Inc.
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