On Thu, Dec 12, 2019 at 2:14 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote: > On Thu, Dec 12, 2019 at 07:56:26AM -0500, Michael S. Tsirkin wrote: > > On Thu, Dec 12, 2019 at 01:36:24PM +0100, Stefano Garzarella wrote: > > > On Wed, Dec 11, 2019 at 11:03:07AM -0500, Michael S. Tsirkin wrote: > > > > On Fri, Dec 06, 2019 at 03:39:12PM +0100, Stefano Garzarella wrote: > > > > > When we receive a new packet from the guest, we check if the > > > > > src_cid is correct, but we forgot to check the dst_cid. > > > > > > > > > > The host should accept only packets where dst_cid is > > > > > equal to the host CID. > > > > > > > > > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx> > > > > > > > > Stefano can you clarify the impact pls? > > > > > > Sure, I'm sorry I didn't do it earlier. > > > > > > > E.g. is this needed on stable? Etc. > > > > > > This is a better analysis (I hope) when there is a malformed guest > > > that sends a packet with a wrong dst_cid: > > > - before v5.4 we supported only one transport at runtime, so the sockets > > > in the host can only receive packets from guests. In this case, if > > > the dst_cid is wrong, maybe the only issue is that the getsockname() > > > returns an inconsistent address (the cid returned is the one received > > > from the guest) > > > > > > - from v5.4 we support multi-transport, so the L1 VM (e.g. L0 assigned > > > cid 5 to this VM) can have both Guest2Host and Host2Guest transports. > > > In this case, we have these possible issues: > > > - L2 (or L1) guest can use cid 0, 1, and 2 to reach L1 (or L0), > > > instead we should allow only CID_HOST (2) to reach the level below. > > > Note: this happens also with not malformed guest that runs Linux v5.4 > > > - if a malformed L2 guest sends a packet with the wrong dst_cid, for example > > > instead of CID_HOST, it uses the cid assigned by L0 to L1 (5 in this > > > example), this packets can wrongly queued to a socket on L1 bound to cid 5, > > > that only expects connections from L0. > > > > Oh so a security issue? > > > > It seems so, I'll try to see if I can get a real example, > maybe I missed a few checks. I was wrong! Multi-transport will be released with v5.5, which will contain this patch. Linux <= v5.4 are safe, with the exception of the potential wrong address returned by getsockname(). In addition, trying Linux <= v5.4 (both guests and host), I found that userspace applications can use any dst_cid to reach the host. It is not a security issue but for sure a wrong semantics. Maybe we should still consider to backport this patch on stables to get the right semantics. Thanks, Stefano _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
