On Thu, Jun 18, 2015 at 11:12:24AM +0200, Igor Mammedov wrote: > On Wed, 17 Jun 2015 18:30:02 +0200 > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > On Wed, Jun 17, 2015 at 06:09:21PM +0200, Igor Mammedov wrote: > > > On Wed, 17 Jun 2015 17:38:40 +0200 > > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > > > > On Wed, Jun 17, 2015 at 05:12:57PM +0200, Igor Mammedov wrote: > > > > > On Wed, 17 Jun 2015 16:32:02 +0200 > > > > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > > > > > > > > On Wed, Jun 17, 2015 at 03:20:44PM +0200, Paolo Bonzini wrote: > > > > > > > > > > > > > > > > > > > > > On 17/06/2015 15:13, Michael S. Tsirkin wrote: > > > > > > > > > > Considering userspace can be malicious, I guess yes. > > > > > > > > > I don't think it's a valid concern in this case, > > > > > > > > > setting limit back from 509 to 64 will not help here in any > > > > > > > > > way, userspace still can create as many vhost instances as > > > > > > > > > it needs to consume memory it desires. > > > > > > > > > > > > > > > > Not really since vhost char device isn't world-accessible. > > > > > > > > It's typically opened by a priveledged tool, the fd is > > > > > > > > then passed to an unpriveledged userspace, or permissions > > > > > > > > dropped. > > > > > > > > > > > > > > Then what's the concern anyway? > > > > > > > > > > > > > > Paolo > > > > > > > > > > > > Each fd now ties up 16K of kernel memory. It didn't use to, so > > > > > > priveledged tool could safely give the unpriveledged userspace > > > > > > a ton of these fds. > > > > > if privileged tool gives out unlimited amount of fds then it > > > > > doesn't matter whether fd ties 4K or 16K, host still could be DoSed. > > > > > > > > > > > > > Of course it does not give out unlimited fds, there's a way > > > > for the sysadmin to specify the number of fds. Look at how libvirt > > > > uses vhost, it should become clear I think. > > > then it just means that tool has to take into account a new limits > > > to partition host in sensible manner. > > > > Meanwhile old tools are vulnerable to OOM attacks. > I've chatted with libvirt folks, it doesn't care about how much memory > vhost would consume nor do any host capacity planning in that regard. Exactly, it's up to host admin. > But lets assume that there are tools that do this so > how about instead of hardcoding limit make it a module parameter > with default set to 64. That would allow users to set higher limit > if they need it and nor regress old tools. it will also give tools > interface for reading limit from vhost module. And now you need to choose between security and functionality :( > > > > > Exposing limit as module parameter might be of help to tool for > > > getting/setting it in a way it needs. > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
