Macos – How to share the Ethernet connection over Wi-Fi on OS X

On your Mac: System Preferences -> Sharing -> Internet Sharing

Share internet From Airport via Ethernet (the wording on that page of System Prefs is pretty close)

On Ubuntu: Disable then re-enable the network and let it use DHCP to automatically get an IP and settings.

Unless you've customised your Mac's settings and firewall this should just work.

The easiest solution I have found for wireless networking is to get a wireless router. This allows you to have a dedicated machine that is designed for this very purpose. It also gives you added security of not having your machine directly connected to the internet.

Make sure the wireless card is good by having your laptop connect to a known good hot spot. It could be that a bad device is causing problems. I doubt that your virus scanner is preventing you from connecting to the internet. A firewall could cause problems if it is setup to block outbound traffic. You stated that you disabled both and you still have problems so it is probably a configuration issue. Use tools like ping and tracert to determin what you can talk to. Check your ip settings with ipconfig and make sure that you are getting the correct DHCP information.

If you don't want to do that, then you might try using a third party hotspot tool like Connectify. It can setup your network without you knowing much. Other than that, make sure that you are following the correct steps to create the ICS connection.

Hope this helps,