[Qemu-devel] [Bug 1628971] Re: -netdev user: guestfwd doesn't work

[T. Huth]

Not sure whether this is really a bug or working as intended - but
apparently, the server IP address from the guest point of view (before
the NAT) has to be in the same subnet as the guest itself. So everything
should work fine if you use something like this in your first example:

 -netdev
'user,id=net0,hostfwd=tcp::2222-:22,guestfwd=tcp:10.0.2.200:1234-cmd:nc
192.168.1.46 8842'

(i.e. just replace the 1.2.3.4 with 10.0.2.200)

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https://bugs.launchpad.net/bugs/1628971

Title:
  -netdev user: guestfwd doesn't work

Status in QEMU:
  New

Bug description:
  Hello!

  QEMU emulator version 2.6.1 (Debian 1:2.6.1+dfsg-0ubuntu4), Copyright
  (c) 2003-2008 Fabrice Bellard

  The IP address 192.168.1.46 is assigned to eth0.

  qemu-system-x86_64 \
      -no-hpet \
      -nodefconfig \
      -machine accel=kvm \
      -cpu host \
      -smp 2 \
      -drive if=virtio,file=yakkety-server-cloudimg-amd64.img \
      -device virtio-net-pci,netdev=net0 \
      -netdev 
'user,id=net0,hostfwd=tcp::2222-:22,guestfwd=tcp:1.2.3.4:1234-cmd:nc 
192.168.1.46 8842' \
      -m 1024 \
      -initrd yakkety-server-cloudimg-amd64-initrd-generic \
      -kernel yakkety-server-cloudimg-amd64-vmlinuz-generic \
      -append 'root=/dev/vda1 modprobe.blacklist=floppy systemd.log_level=debug 
systemd.journald.forward_to_console=1'

  Without the guestfwd=... part everything works nicely. With it I get
  the following message.

  
  qemu-system-x86_64: -netdev 
user,id=net0,hostfwd=tcp::2222-:22,guestfwd=tcp:1.2.3.4:1234-cmd:nc 
192.168.1.46 8842: conflicting/invalid host:port in guest forwarding rule 
'tcp:1.2.3.4:1234-cmd:nc 192.168.1.46 8842'
  qemu-system-x86_64: -netdev 
user,id=net0,hostfwd=tcp::2222-:22,guestfwd=tcp:1.2.3.4:1234-cmd:nc 
192.168.1.46 8842: Device 'user' could not be initialized

  
  But I just compiled c640f2849ee8775fe1bbd7a2772610aa77816f9f, and I get the 
same behavior.

  address@hidden:~/qemu/x86_64-softmmu$ ./qemu-system-x86_64 -net 
'user,guestfwd=tcp:1.2.3.4:1234-cmd:nc 192.168.1.48 80'
  qemu-system-x86_64: -net user,guestfwd=tcp:1.2.3.4:1234-cmd:nc 192.168.1.48 
80: conflicting/invalid host:port in guest forwarding rule 
'tcp:1.2.3.4:1234-cmd:nc 192.168.1.48 80'
  qemu-system-x86_64: -net user,guestfwd=tcp:1.2.3.4:1234-cmd:nc 192.168.1.48 
80: Device 'user' could not be initialized

  
  After poking a bit around it seems that this check fails in slirp/slirp.c: 
(around line 1074)

      if ((guest_addr->s_addr & slirp->vnetwork_mask.s_addr) !=
          slirp->vnetwork_addr.s_addr ||
          guest_addr->s_addr == slirp->vhost_addr.s_addr ||
          guest_addr->s_addr == slirp->vnameserver_addr.s_addr) {
          return -1;
      }

  Because guest_addr, and slirp has equivalent s_addr values.

  x86_64-softmmu/qemu-system-x86_64 -net
  'user,net=10.0.2.0/24,host=10.0.2.2,guestfwd=tcp:12.0.0.2:80-cmd:echo
  ok'

  guest_addr: 12.0.0.2
  vnetwork_mask: 12.0.0.2
  vhost_addr: 12.0.0.2
  vnameserver_addr: 12.0.0.2
  guest_addr & mask: 12.0.0.2

  
  Thanks in advance for looking into this!

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