[squid-users] FTP relay with active client is broken?

Amos Jeffries squid3 at treenet.co.nz
Tue Feb 14 01:58:42 UTC 2017

On 14/02/2017 1:18 a.m., Alex wrote:
>   Well, actually it looks like a bug in squid to me. Some points:
> 1. When client connects with active FTP mode, squid opens a local socket and tries to assign server's IP address to it. So far so good, however this doesn't work (tested in both 'intercept' and 'tproxy' modes):
>    2017/02/13 14:58:51.234| 50,3| comm.cc(347) comm_openex: comm_openex: Attempt open socket for:
>    2017/02/13 14:58:51.234| 50,3| comm.cc(388) comm_openex: comm_openex: Opened socket local= remote=[::] FD 17 flags=1 : family=2, type=1, protocol=6
>    2017/02/13 14:58:51.234| 5,5| comm.cc(420) comm_init_opened: local= remote=[::] FD 17 flags=1 is a new socket
>    2017/02/13 14:58:51.234| 51,3| fd.cc(198) fd_open: fd_open() FD 17
>    2017/02/13 14:58:51.234| commBind: Cannot bind socket FD 17 to (99) Cannot assign requested address
> 2. Ok, we've got the errno. Let's look in comm_apply_flags(). There's something like this in the middle:
>     /* MUST be done before binding or face OS Error: "(99) Cannot assign requested address"... */
>     if ((flags & COMM_TRANSPARENT)) {
>         comm_set_transparent(new_socket);
>     }
>     This means that socket is not IP_TRANSPARENT and can not be bound to arbitrary IP address ('net.ipv4.ip_nonlocal_bind' can fix bind(), but connect() will obviously fail with EINVAL).
> 3. Let's take a look on Ftp::Server::createDataConnection():
>     Comm::ConnectionPointer conn = new Comm::Connection();
>     conn->flags |= COMM_DOBIND;
>     // Use local IP address of the control connection as the source address
>     // of the active data connection, or some clients will refuse to accept.
>     conn->setAddrs(clientConnection->local, cltAddr);
>     Fine, looks reasonable. However, connection has only COMM_DOBIND flag, COMM_TRANSPARENT is missing. AFAIU, we'll never be able to bind and connect a socket...

Good catch. Thank you.

* NAT intercept needs to listen on the local IP of the Squid->server
control connection.
* TPROXY needs to listen on the local IP of the client->Squid control
connection plus the TRANSPARENT flag.

Any chance of a patch?


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