'Setup' section of https://wiki.qemu.org/Features/HelperNetworking says that setuid attribute needs to be turned on for 'qemu-bridge-helper' binary, but it forgets to mention that owner of this file must be root user. Otherwise, setuid bit makes no sense. Looks like in most scenarios this binary already installed with root privileges. But this isn't a case, when you build QEMU from sources and install it in custom location, running 'make install' by non-privileged user. Yes, maybe it's obvious for mature linux users, but it took me a lot of time to figure out why QEMU fails with error: "failed to create tun device: Operation not permitted" (googling this error shows mostly answers like "you just forget setuid"). So, it would be useful to add sudo chown root /usr/local/libexec/qemu-bridge-helper *before* sudo chmod u+s /usr/local/libexec/qemu-bridge-helper
