I suspect a VPN application from Mullvad may have broken some network configuration settings. My system hung while I was using it, and after restarting, I can connect to networks over WiFi and get an IP via DHCP, but I can't access or ping any websites by their domain names. I do get ping response from my router, and from 188.8.131.52, so it seems like it's just domain name resolution that's broken. But I went into my wifi settings and told it to use 184.108.40.206 as the DNS, and I still can't get anywhere.
What can I do from here?
EDIT: I think I've found the root of the problem. It appears that every time NetworkManager sets up a network connection, it's setting the DNS server in /etc/resolv.conf to 127.0.1.1. How do I stop it from doing this?