Re: disablenetwork (v5): Simplify the disablenetwork sendmsg hook.

From: Michael S. Tsirkin
Date: Sun Jan 17 2010 - 13:07:22 EST

On Sun, Jan 17, 2010 at 12:04:32PM -0500, Michael Stone wrote:
> Michael Tsirkin wrote:
>> On Fri, Jan 15, 2010 at 03:12:46AM -0500, Michael Stone wrote:
>>> The idea is that calls like
>>> sendto(fd, buffer, len, 0, NULL, 0);
>>> send(fd, buffer, len, 0)
>>> write(fd, buffer, len)
>>> are all to be permitted but that calls like
>>> sendto(fd, buffer, len, 0, (struct sockadr *) &addr, sizeof(addr));
>>> are to be rejected when the current task's network is disabled on the grounds
>>> that the former calls must use previously connected sockets but that the latter
>>> socket need not have been previously connected.
>>> Signed-off-by: Michael Stone <michael@xxxxxxxxxx>
>> Michael, if I understand correctly, with this patch one could use
>> disablenetwork to pass an af_packet socket bound to a device to a
>> task, and make sure that the task does not use it to inject packets into
>> another device?
> Michael,
> Thanks for writing. If I understand you correctly, you're asking:
> May a network-disabled process use recvmsg() with SCM_RIGHTS control messages
> to receive a file descriptor pointing to previously connected or bound
> AF_PACKET socket and, having received such an fd, may the network-disabled
> process use the socket normally?
> If I've understood correctly, then the answer is "yes, to the extent that you
> can't do stupid things with sendmsg(), fnctl(), ioctl(), and friends."
> I intend to look more carefully at the ability to use those calls to do stupid
> things in coming weeks.
> Does this help?
> Regards,
> Michael
> P.S. - Incidentally, what is the nature of your interest?

We discussed using af_packet sockets for networking in qemu. qemu is a
large project so it might not be a great idea to run it as root all the
time: a better idea is to e.g. get fd from a priveledged server.
However, we'd like to limit qemu even more, so that it can only use the
fd for send/receive.

> (And was your question intentionally or accidentally off-list?)

Oops. Adding it back.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at