Slirp has been moved to an external project now. If this is still an issue,
please report the problem there instead:
https://gitlab.freedesktop.org/slirp/libslirp
** Changed in: qemu
Status: New => Won't Fix
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https://bugs.launchpad.net/bugs/1668273
Title:
DoS possible on - a QEMU process using userspace SLIRP?
Status in QEMU:
Won't Fix
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.
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