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Bugtraq archives for 4th quarter (Oct-Dec) 1997: Re: Linux inetd..

Re: Linux inetd..

Alan Cox (alanLXORGUK.UKUU.ORG.UK)
Tue, 2 Dec 1997 20:50:01 +0000 

> Now you may be wondering why does a write to the socket returned by
> accept() generates a SIGPIPE. This bring us to the second issue. It seems
> that at least under Linux 2.0.X accept will return a socket in the
> received queue if it is not in the SYN_SENT or SYN_RECV state, even when
> it has not gone through the ESTABLISHED state.
>
> By doing a stealth scan on the port the socket goes from the SYN_RECV
> state to the CLOSED state. When you try to read from such a socket you
> get a SIGPIPE. The sematics of Linux's accept seems to be non-standard. I
> wonder what else breaks by not handling SIGPIPE.

On that issue you are a little astray. Linux merely made the window for
the inetd problem a bit larger. You can hit a box betwen the accept
returning towards user space and the write() with a seperate RST frame
regardless of what accept returns. If generic BSD has this missing
SIGPIPE I venture to say that if you can hit the precise boundary needed
you can bring down inetd there too.

ie
                SYN/ SYN-RECV/ ACK
        accept()
                RST
        write()
        SIGPIPE

Alan