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Re: FreeBSD socket loss (a.k.a. MSIE DoS attack)


Lars Povlsen wrote:
Hi All!

I have run into a weird occurrence of total socket buffer drainage with the FreeBSD network stack (IPv4).

The problem is triggered by MSIE going bezerk while rendering an Ajax/DOM style, graphics heavy, web page. It goes into a mode of a series of spastic connnects to the (eCos) HTTP server, request a graphic object, followed immediately by a RST. Then a new connection, etc. The browser manages to get the job done, at the expense of TCP connections and - worse - the FreeBSD stack loosing socket buffers - forever!

When the network stack is void of buffers, exiting the browser only frees *1* socket buffer. And waiting > 10 minutes does not uncover more buffers from the depths of the stack.

While I realize that MSIE is acting up - BIG TIME - I hate that it can cause semi-permanent damage to the operation of my system. Does anybody have any clues as to how to uncover the leak? I have a workaround to the browser behavior, but thats dancing around the issue, really. The browser does dot always behave like this, but I guess I can hack up a perl script to recreate the problem more reliantly if needed...

I have attached (part of) a Ethereal summary to display the TCP/browser access pattern. The server is at 10.10.132.15, the client browser at 10.10.130.96. Needless to say, FF works like a champ...


If you think you can produce a small-ish test driver (perl?) which can cause this, I think that would be the best way forward. Then we can duplicate the problem and try to attack it.

--
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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