[Qemu-devel] Connection breaks for macvtap

[Qemu-devel] Connection breaks for macvtap

[Richa Marwaha]

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Hi

I am trying to run some KVM fuzz testing where I have a tool called scapy
running on my host and guest which changes the data in the IP header of the
packages and send it out to the host and vice versa. I have macvtap setup
on my host (have tried both VEPA and Bridge mode).
My ssh connection to my guest breaks down after having send just 22 packets
and also the gnome crashes. I see the following message in the dmesg

dbus[545]: [system] Rejected send message, 2 matched rules;
type="method_return", sender=":1.0" (uid=0 pid=499
comm="/usr/lib/systemd/systemd-logind ") interface="(unset)"
member="(unset)" error name="(unset)" requested_reply="0"
destination=":1.17" (uid=42 pid=658 comm="/usr/bin/gnome-session -f --debug
")

The connection to the guest restart but wanted to know what makes it
breakdown.

Regards,
Richa Marwaha

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Re: [Qemu-devel] Connection breaks for macvtap

[Anthony Liguori]

Richa Marwaha <rmarwah@us.ibm.com> writes:

> Hi
>
> I am trying to run some KVM fuzz testing where I have a tool called scapy
> running on my host and guest which changes the data in the IP header
> of the

FWIW, I don't think you'll gain a lot from this.  QEMU does not ever
look at a packet beyond the MAC address (and perhaps any vlan tags in
the ethernet header).  That far up the stack is strictly
application/network infrastructure land.

So if your goal is to fuzz test the Linux networking code, then this
approach is fine.  But it's unlikely to do anything useful with QEMU itself.

> packages and send it out to the host and vice versa. I have macvtap setup
> on my host (have tried both VEPA and Bridge mode).

Unless you have an explicit reason to use it, I'd steer away from
macvtap.  It's not commonly used.

> My ssh connection to my guest breaks down after having send just 22
> packets

If you're munging random IP packets, you're going to lose connections
:-)  That's pretty much a given.  I'm not surprised at all it happens
this quickly.

> and also the gnome crashes. I see the following message in the dmesg
>
> dbus[545]: [system] Rejected send message, 2 matched rules;
> type="method_return", sender=":1.0" (uid=0 pid=499
> comm="/usr/lib/systemd/systemd-logind ") interface="(unset)"
> member="(unset)" error name="(unset)" requested_reply="0"
> destination=":1.17" (uid=42 pid=658 comm="/usr/bin/gnome-session -f --debug
> ")

I don't know what this is but if you were doing something like remoting
X over an ssh session, this wouldn't be much of a surprise.

Regards,

Anthony Liguori

>
> The connection to the guest restart but wanted to know what makes it
> breakdown.
>
> Regards,
> Richa Marwaha