Messages in this thread Patch in this message | | | Date | Thu, 10 Jan 2013 22:47:49 +0800 | From | Jason Wang <> | Subject | Re: [PATCH] tun: avoid owner checks on IFF_ATTACH_QUEUE |
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On 01/10/2013 10:41 PM, Michael S. Tsirkin wrote: > On Thu, Jan 10, 2013 at 10:27:20PM +0800, Jason Wang wrote: >> On 01/10/2013 10:19 PM, Michael S. Tsirkin wrote: >>> On Thu, Jan 10, 2013 at 10:08:03PM +0800, Jason Wang wrote: >>>> On 01/10/2013 07:31 PM, Michael S. Tsirkin wrote: >>>>> At the moment, we check owner when we enable queue in tun. >>>>> This seems redundant and will break some valid uses >>>>> where fd is passed around: I think TUNSETOWNER is there >>>>> to prevent others from attaching to a persistent device not >>>>> owned by them. Here the fd is already attached, >>>>> enabling/disabling queue is more like read/write. >>>> It also change the number of queues of the tuntap, maybe we should limit >>>> this. >>> Number of active queues? Why does it matter? >>> Max number of queues is already limited by SETIFF. >> Yes the number of active(real) queues in the kernel net device and this >> changing may introduce other events such uevent. > How can it trigger a uevent?
netif_set_real_num_{tx|rx}_queues() will update the queue kobjects which may trigger an uevent. > >> With this patch, even >> if a owner is set for tap, every user could change the number of real >> queues which I don't think is not expected. Without this patch, we can >> limit a user that just do read and write. > In the end if you want very fine tuned security policy you have to > use an LSM. > > Here we are talking about the expected usage without an LSM. > There, enabling/disabling queues is just an optimization: > if an application wants to process data from a single thread > it's better off getting it through a single fd. > Having to channel threading changes through a priveledged > proxy would be very awkward.
Yes, but we have something similar like bridge-helper in qemu which create devices through a privileged proxy. >>>> Note that if management layer does not call TUNSETOWNER, the check >>>> is just a nop. So if management layer want to limit the behavior, it's >>>> its duty to do this correctly. >>> The point is that management limits tun to allow SETIFF from libvirt >>> only, then passes the fds to qemu. >> Yes, but looks like libvirt does not call TUNSETOWNER before passing it >> to qemu, so we're ok even without this patch. And if libvirt want to do >> this, it can just call TUNSETOWNER to the user of qemu. > No, that would allow qemu to do SETIFF which we don't want.
True, I was wrong. > >>>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> >>>>> >>>>> --- >>>>> >>>>> Note: this is unrelated to Stefan's bugfix. >>>>> >>>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >>>>> index fbd106e..78e3225 100644 >>>>> --- a/drivers/net/tun.c >>>>> +++ b/drivers/net/tun.c >>>>> @@ -1789,10 +1792,8 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr) >>>>> tun = tfile->detached; >>>>> if (!tun) >>>>> ret = -EINVAL; >>>>> - else if (tun_not_capable(tun)) >>>>> - ret = -EPERM; >>>>> else >>>>> ret = tun_attach(tun, file); >>>>> } else if (ifr->ifr_flags & IFF_DETACH_QUEUE) { >>>>> tun = rcu_dereference_protected(tfile->tun, >>>>> lockdep_rtnl_is_held()); >>> -- >>> To unsubscribe from this list: send the line "unsubscribe netdev" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html
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