ipv4 tcp autobind problem

[Kovacs Krisztian (hidden@balabit.hu)]

  Hi,

  While testing the tproxy patch for linux-2.4 
(http://www.balabit.com/downloads/tproxy/linux-2.4), Stas Grabois has 
found a quite strange aspect of Linux 2.4 TCP. Imagine the following 
scenario: you create a new socket (AF_INET, SOCK_STREAM), bind it to local 
port 0, and try to connect() to a closed port. Of course, the peer sends 
back an RST, indicating no one is listening on that port. However, if your 
application does not care about the return value of connect(), and calls 
send() on the not connected socket, inet_autobind() is called and a new 
local port is allocated for the socket. So, besides returning an error, 
there is also a side effect of the send(). The same thing happens with an 
established TCP session if the peer sends an RST between two send() calls, 
the second call will autobind the socket, and then return error.
  Is this behaviour intentional? Shouldn't inet_sendmsg() check for an 
error before calling inet_autobind()?

--
  Regards,
    Krisztian KOVACS


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