connect: improve binding to local ports on Windows #8528
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to use GetTcpTable2() and GetTcp6Table2()
There is a configuration parameter in windows registry called TcpTimedWaitDelay that determines the time that a connection stays in the TIME_WAIT state when it is closing. It's minimum and default value is 30 seconds. As long as a connection is in the TIME_WAIT state, the socket pair cannot be re-used, BUT bind() still returns 0 in this case. curl now can detect the state of a given port using GetTcpTable2() for IPv4 connections and avoids to bind that port if the state is TIME_WAIT Fixes: curl#8112 Bug: curl#8112 Reported-by: gclinch on github
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This is an interesting solution and I am very interested in what others will think of it. My initial thoughts are: I think it would probably have some cost to enumerate. The bind address would have to be checked as well as the port. IPv4 / IPv6 (af == AF_INET6) differences, the latter needs IPv6 enumeration check. Also how reliable is it if the port is in some other state and the check passes because it's not timewait and then on connect same problem? Also I wonder how malware detection software is going to react to enumerating the entire table of tcp. |
GetTcp6Table2 can be used for IPv6 connections.
I did some tests and yes... if the port is in some other state we may face the same problem (E.g. FIN_WAIT1). so basically bind should only be called if the port is not in any state defined in the MIB_TCP_STATE. |
bagder
changed the title
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I need more guidance and feedback on this proposal from people using and knowing Windows. |
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This improvement proposal has not received much interest and I cannot deem the necessity myself. As such, I cannot merge this. Sorry. |
There is a configuration parameter in windows registry
called TcpTimedWaitDelay that determines the time that a
connection stays in the TIME_WAIT state when it is closing.
It's minimum and default value is 30 seconds.
As long as a connection is in the TIME_WAIT state, the socket pair
cannot be re-used, BUT bind() still returns 0 in this case.
curl now can detect the state of a given port using
GetTcpTable2() for IPv4 connections and avoids to bind that port
if the state is TIME_WAIT
ref: https://docs.microsoft.com/en-us/troubleshoot/windows-client/networking/tcpip-and-nbt-configuration-parameters#optional-tcpip-parameters-that-you-can-configure-by-using-registry-editor
Fixes: #8112
Reported-by: gclinch on github