On Mon, Jun 26, 2023 at 8:29 AM Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > Reviving Günther's suggestion to deny a set of network protocols: > > On 14/03/2023 14:28, Mickaël Salaün wrote: > > > > On 13/03/2023 18:16, Konstantin Meskhidze (A) wrote: > >> > >> > >> 2/24/2023 1:17 AM, Günther Noack пишет: > > [...] > > >>> > >>> * Given the list of obscure network protocols listed in the socket(2) > >>> man page, I find it slightly weird to have rules for the use of TCP, > >>> but to leave less prominent protocols unrestricted. > >>> > >>> For example, a process with an enabled Landlock network ruleset may > >>> connect only to certain TCP ports, but at the same time it can > >>> happily use Bluetooth/CAN bus/DECnet/IPX or other protocols? > >> > >> We also have started a discussion about UDP protocol, but it's > >> more complicated since UDP sockets does not establish connections > >> between each other. There is a performance problem on the first place here. > >> > >> I'm not familiar with Bluetooth/CAN bus/DECnet/IPX but let's discuss it. > >> Any ideas here? > > > > All these protocols should be handled one way or another someday. ;) > > > > > >> > >>> > >>> I'm mentioning these more obscure protocols, because I doubt that > >>> Landlock will grow more sophisticated support for them anytime soon, > >>> so maybe the best option would be to just make it possible to > >>> disable these? Is that also part of the plan? > >>> > >>> (I think there would be a lot of value in restricting network > >>> access, even when it's done very broadly. There are many programs > >>> that don't need network at all, and among those that do need > >>> network, most only require IP networking. > > > > Indeed, protocols that nobody care to make Landlock supports them will > > probably not have fine-grained control. We could extend the ruleset > > attributes to disable the use (i.e. not only the creation of new related > > sockets/resources) of network protocol families, in a way that would > > make sandboxes simulate a kernel without such protocol support. In this > > case, this should be an allowed list of protocols, and everything not in > > that list should be denied. This approach could be used for other kernel > > features (unrelated to network). > > > > > >>> > >>> Btw, the argument for more broad disabling of network access was > >>> already made at https://cr.yp.to/unix/disablenetwork.html in the > >>> past.) > > > > This is interesting but scoped to a single use case. As specified at the > > beginning of this linked page, there must be exceptions, not only with > > AF_UNIX but also for (the newer) AF_VSOCK, and probably future ones. > > This is why I don't think a binary approach is a good one for Linux. > > Users should be able to specify what they need, and block the rest. > > Here is a design to be able to only allow a set of network protocols and > deny everything else. This would be complementary to Konstantin's patch > series which addresses fine-grained access control. > > First, I want to remind that Landlock follows an allowed list approach > with a set of (growing) supported actions (for compatibility reasons), > which is kind of an allow-list-on-a-deny-list. But with this proposal, > we want to be able to deny everything, which means: supported, not > supported, known and unknown protocols. > I think this makes sense. ChomeOS can use it at the process level: disable network, allow VSOCK only, allow TCP only, etc. > We could add a new "handled_access_socket" field to the landlock_ruleset > struct, which could contain a LANDLOCK_ACCESS_SOCKET_CREATE flag. > > If this field is set, users could add a new type of rules: > struct landlock_socket_attr { > __u64 allowed_access; > int domain; // see socket(2) > int type; // see socket(2) > } > Do you want to add "int protocol" ? which is the third parameter of socket(2) According to protocols(5), the protocols are defined in: https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml It is part of IPv4/IPV6 header: https://www.rfc-editor.org/rfc/rfc791.html#section-3.1 https://www.rfc-editor.org/rfc/rfc8200.html#section-3 > The allowed_access field would only contain > LANDLOCK_ACCESS_SOCKET_CREATE at first, but it could grow with other > actions (which cannot be handled with seccomp): > - use: walk through all opened FDs and mark them as allowed or denied > - receive: hook on received FDs > - send: hook on sent FDs > also bind, connect, accept. > We might also use the same approach for non-socket objects that can be > identified with some meaningful properties. > > What do you think? -Jeff
