General :: Get Internet Access Via Firefox On MachineB By Creating A Series Of SOCKS Proxy Via SSH?

I've been doing some security testing in a lab environment that does not have direct internet access. From home to connect to my lab machine, I

1. SSH to machineA.
2. SSH from machineA to machineB

where machineB is my actual lab machine. neither machineA or machineB allow anything other than SSH, and machineB is only accessible from machineA. However, I really need to run yum on machineB.I have managed to get internet access via Firefox on machineB by creating a series of SOCKS proxy via SSH.

1. machineB: ssh -L 12345:localhost:12345 user@machineA
2. machineA: ssh -D 12345 user@machineC
3. machineB: configure firefox to use socks proxy, localhost, 12345

where machineC has internet without limits placed. This is the only way I have managed to get internet working. I tried using ssh -L all the way from machineB->machineA->machineC but it didn't work (even when setting Firefox to use http proxy). I tried using ssh -D all the way, but again that doesn't work either. I do have access via Firefox using socks proxy. However, yum update fails to retrieve mirror list, and from what I have found I don't believe yum supports socks proxy directly. Instead, it uses http_proxy / ftp_proxy.how to get yum to go out over the SOCKS proxy I created (same one using in Firefox)? It seems like since Firefox can access the internet and everything without issues, i should be able to get yum to tunnel through the same connection to access everything.... I tried

>export http_proxy="http://localhost:12345"
(yum.conf) proxy="http://localhost:12345"