On Thu, Apr 03, 2025 at 11:33:14AM +0200, Stefano Garzarella wrote: > On Wed, Apr 02, 2025 at 03:28:19PM -0700, Bobby Eshleman wrote: > > On Wed, Apr 02, 2025 at 03:18:13PM -0700, Bobby Eshleman wrote: > > > On Wed, Apr 02, 2025 at 10:21:36AM +0100, Daniel P. Berrangé wrote: > > > > On Wed, Apr 02, 2025 at 10:13:43AM +0200, Stefano Garzarella wrote: > > > > > On Wed, 2 Apr 2025 at 02:21, Bobby Eshleman <bobbyeshle...@gmail.com> > > > > > wrote: > > > > > > > > > > > > I do like Stefano's suggestion to add a sysctl for a "strict" mode, > > > > > > Since it offers the best of both worlds, and still tends > > > > > > conservative in > > > > > > protecting existing applications... but I agree, the non-strict mode > > > > > > vsock would be unique WRT the usual concept of namespaces. > > > > > > > > > > Maybe we could do the opposite, enable strict mode by default (I think > > > > > it was similar to what I had tried to do with the kernel module in > > > > > v1, I > > > > > was young I know xD) > > > > > And provide a way to disable it for those use cases where the user > > > > > wants > > > > > backward compatibility, while paying the cost of less isolation. > > > > > > > > I think backwards compatible has to be the default behaviour, otherwise > > > > the change has too high risk of breaking existing deployments that are > > > > already using netns and relying on VSOCK being global. Breakage has to > > > > be opt in. > > > > > > > > > I was thinking two options (not sure if the second one can be done): > > > > > > > > > > 1. provide a global sysfs/sysctl that disables strict mode, but this > > > > > then applies to all namespaces > > > > > > > > > > 2. provide something that allows disabling strict mode by namespace. > > > > > Maybe when it is created there are options, or something that can be > > > > > set later. > > > > > > > > > > 2 would be ideal, but that might be too much, so 1 might be enough. In > > > > > any case, 2 could also be a next step. > > > > > > > > > > WDYT? > > > > > > > > It occured to me that the problem we face with the CID space usage is > > > > somewhat similar to the UID/GID space usage for user namespaces. > > > > > > > > In the latter case, userns has exposed /proc/$PID/uid_map & gid_map, to > > > > allow IDs in the namespace to be arbitrarily mapped onto IDs in the > > > > host. > > > > > > > > At the risk of being overkill, is it worth trying a similar kind of > > > > approach for the vsock CID space ? > > > > > > > > A simple variant would be a /proc/net/vsock_cid_outside specifying a set > > > > of CIDs which are exclusively referencing /dev/vhost-vsock associations > > > > created outside the namespace. Anything not listed would be exclusively > > > > referencing associations created inside the namespace. > > > > > > > > A more complex variant would be to allow a full remapping of CIDs as is > > > > done with userns, via a /proc/net/vsock_cid_map, which the same three > > > > parameters, so that CID=15 association outside the namespace could be > > > > remapped to CID=9015 inside the namespace, allow the inside namespace > > > > to define its out association for CID=15 without clashing. > > > > > > > > IOW, mapped CIDs would be exclusively referencing /dev/vhost-vsock > > > > associations created outside namespace, while unmapped CIDs would be > > > > exclusively referencing /dev/vhost-vsock associations inside the > > > > namespace. > > > > > > > > A likely benefit of relying on a kernel defined mapping/partition of > > > > the CID space is that apps like QEMU don't need changing, as there's > > > > no need to invent a new /dev/vhost-vsock-netns device node. > > > > > > > > Both approaches give the desirable security protection whereby the > > > > inside namespace can be prevented from accessing certain CIDs that > > > > were associated outside the namespace. > > > > > > > > Some rule would need to be defined for updating the > > > > /proc/net/vsock_cid_map > > > > file as it is the security control mechanism. If it is write-once then > > > > if the container mgmt app initializes it, nothing later could change > > > > it. > > > > > > > > A key question is do we need the "first come, first served" behaviour > > > > for CIDs where a CID can be arbitrarily used by outside or inside > > > > namespace > > > > according to whatever tries to associate a CID first ? > > > > > > I think with /proc/net/vsock_cid_outside, instead of disallowing the CID > > > from being used, this could be solved by disallowing remapping the CID > > > while in use? > > > > > > The thing I like about this is that users can check > > > /proc/net/vsock_cid_outside to figure out what might be going on, > > > instead of trying to check lsof or ps to figure out if the VMM processes > > > have used /dev/vhost-vsock vs /dev/vhost-vsock-netns. > > Yes, although the user in theory should not care about this information, > right? > I mean I don't even know if it makes sense to expose the contents of > /proc/net/vsock_cid_outside in the namespace. > > > > > > > Just to check I am following... I suppose we would have a few typical > > > configurations for /proc/net/vsock_cid_outside. Following uid_map file > > > format of: > > > "<local cid start> <global cid start> <range > > > size>" > > This seems to relate more to /proc/net/vsock_cid_map, for > /proc/net/vsock_cid_outside I think 2 parameters are enough > (CID, range), right? >
True, yes vsock_cid_map. > > > > > > 1. Identity mapping, current namespace CID is global CID (default > > > setting for new namespaces): > > > > > > # empty file > > > > > > OR > > > > > > 0 0 4294967295 > > > > > > 2. Complete isolation from global space (initialized, but no mappings): > > > > > > 0 0 0 > > > > > > 3. Mapping in ranges of global CIDs > > > > > > For example, global CID space starts at 7000, up to 32-bit max: > > > > > > 7000 0 4294960295 > > > > > > Or for multiple mappings (0-100 map to 7000-7100, 1000-1100 map to > > > 8000-8100) : > > > > > > 7000 0 100 > > > 8000 1000 100 > > > > > > > > > One thing I don't love is that option 3 seems to not be addressing a > > > known use case. It doesn't necessarily hurt to have, but it will add > > > complexity to CID handling that might never get used? > > Yes, as I also mentioned in the previous email, we could also do a > step-by-step thing. > > IMHO we can define /proc/net/vsock_cid_map (with the structure you just > defined), but for now only support 1-1 mapping (with the ranges of > course, I mean the first two parameters should always be the same) and > then add option 3 in the future. > makes sense, sgtm! > > > > > > Since options 1/2 could also be represented by a boolean (yes/no > > > "current ns shares CID with global"), I wonder if we could either A) > > > only support the first two options at first, or B) add just > > > /proc/net/vsock_ns_mode at first, which supports only "global" and > > > "local", and later add a "mapped" mode plus /proc/net/vsock_cid_outside > > > or the full mapping if the need arises? > > I think option A is the same as I meant above :-) > Indeed. > > > > > > This could also be how we support Option 2 from Stefano's last email of > > > supporting per-namespace opt-in/opt-out. > > Hmm, how can we do it by namespace? Isn't that global? > I think the file path is global but the contents are tied per-namespace, according to the namespace of the process that called open() on it. This way the container mgr can write-once lock it, and the namespace processes can read it? > > > > > > Any thoughts on this? > > > > > > > Stefano, > > > > Would only supporting 1/2 still support the Kata use case? > > I think so, actually I was thinking something similar in the message I just > sent. > > By default (if the file is empty), nothing should change, so that's fine > IMO. As Paolo suggested, we absolutely have to have tests to verify these > things. > Sounds like a plan! I'm working on the new vsock vmtest now and will include the new tests in the next rev. Also, I'm thinking we should protect vsock_cid_map behind a capability, but I'm not sure which one is correct (CAP_NET_ADMIN?). WDYT? Thanks!
