On 16/06/17 22:26, Julien Gomes wrote: > On 06/15/2017 06:00 AM, Nikolay Aleksandrov wrote: >> On 15/06/17 14:44, Nikolay Aleksandrov wrote: >>> On 15/06/17 14:33, Nikolay Aleksandrov wrote: >>>> On 15/06/17 00:51, Julien Gomes wrote: >>>>> Hi Nikolay, >>>>> >>>>> On 06/14/2017 05:04 AM, Nikolay Aleksandrov wrote: >>>>> >>>>>> This has been on our todo list and I'm definitely interested in the >>>>>> implementation. >>>>>> A few things that need careful consideration from my POV. First are the >>>>>> security >>>>>> implications - this sends rtnl multicast messages but the rtnl socket has >>>>>> the NL_CFG_F_NONROOT_RECV flag thus allowing any user on the system to >>>>>> listen in. >>>>>> This would allow them to see the full packets and all reports (granted >>>>>> they can see >>>>>> the notifications even now), but the full packet is like giving them the >>>>>> opportunity >>>>>> to tcpdump the PIM traffic. >>>>> I definitely see how this can be an issue. >>>>> From what I see, this means that either the packet should be >>>>> transmitted another way, or another Netlink family should be used. >>>>> >>>>> NETLINK_ROUTE looks to be the logical family to choose though, >>>>> but then I do not see a proper other way to handle this. >>>> Right, currently me neither, unless it provides a bind callback when >>>> registering >>>> the kernel socket. >>>> >>>>> However I may just not be looking into the right direction, >>>>> maybe you currently have another approach in mind? >>>> I haven't gotten around to make (or even try) them but I was thinking >>>> about 2 options >>>> ending up with a similar result: >>>> >>>> 1) genetlink >>>> It also has the NONROOT_RECV flag, but it also allows for a callback - >>>> mcast_bind() >>>> which can be used to filter. >>>> >>>> or >>>> >>>> 2) Providing a bind callback to the NETLINK_ROUTE socket. >>>> >>> Ah nevermind, these cannot be used for filtering currently, so it seems >>> the netlink interface would need to be extended too if going down this road. >>> >> Sorry for the multiple emails, just to be thorough - again if going down this >> road all of these would obviously require a different group to bind to in >> order >> to be able to filter on it, because users must keep receiving their >> notifications >> for the ipmr one. > > Actually, using a bind callback for NETLINK_ROUTE with a new group, > without netlink interface extension, could work. > > I quickly tested something like this: >> static int rtnetlink_bind(struct net *net, int group) >> { >> switch (group) { >> case RTNLGRP_IPV4_MROUTE_R: >> case RTNLGRP_IPV6_MROUTE_R: >> if (!ns_capable(net->user_ns, CAP_NET_ADMIN)) >> return -EPERM; >> break; >> } >> return 0; >> } > > With the addition of one/two groups this does restrict the reports' > potential listeners. > The group names here are just placeholders, I am not especially fixed > on these ones. > > It is not perfect as this would introduce groups with specific > requirements in NETLINK_ROUTE, but I think it can be decent. > > What do you think about this? >
Oh yes, that is exactly what I had in mind. I missed that the netns is passed to the bind function. Thanks, Nik