security of your machine when connecting to exposed server via ssh
 

if somebody gains control of the server i'm connecting to using ssh (creating a socks tunnel)
does he have access to my machine?
i am behind a router, acting as a firewall, not giving access to ports on my machine from outside the network

how about when forwarding a single port? (port 80), do they still have access?

Controlling the remote host you SSH to or through means the perp in theory controls whatever you execute on, get from or send through that host. Since you only tunnel encrypted SSH traffic through the remote host and don't allow new connections to your LAN machine behind your LAN router / firewall and only use SSH with pubkey auth and your remote host uses a unique password or (better) pass-phrase the risk of the perp finding a way in through that connection is infinitesimal.

since the way ssh works for tunneling is creating another ssh connection from server to host(my machine), doesnt this mean they have access for execution of commands?

Looks like something you could do the groundwork for yourself: create your SSH tunnel (you never listed if you were using a reverse tunnel or not BTW), log in on the remote host, then try to execute commands through your tunnel.

dear unSpawn
i'm using the reverse tunnel for bypassing some restriction (a SOCKS proxy), that's what the -D option does (reverse tunnel), right?

"-D" just means dynamic and using it doesn't make it a "reverse tunnel".

thank you unSpawn!! a lot