Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 29 May 2024 18:50:34 -0600 | From | Tahera Fahimi <> | Subject | Re: [PATCH v2] landlock: Add abstract unix socket connect restrictions |
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On Tue, Apr 30, 2024 at 05:24:45PM +0200, Mickaël Salaün wrote: > On Wed, Apr 10, 2024 at 04:24:30PM -0600, Tahera Fahimi wrote: > > On Tue, Apr 02, 2024 at 11:53:09AM +0200, Mickaël Salaün wrote: > > > Thanks for this patch. Please CC the netdev mailing list too, they may > > > be interested by this feature. I also added a few folks that previously > > > showed their interest for this feature. > > > > > > On Thu, Mar 28, 2024 at 05:12:13PM -0600, TaheraFahimi wrote: > > > > Abstract unix sockets are used for local interprocess communication without > > > > relying on filesystem. Since landlock has no restriction for connecting to > > > > a UNIX socket in the abstract namespace, a sandboxed process can connect to > > > > a socket outside the sandboxed environment. Access to such sockets should > > > > be scoped the same way ptrace access is limited. > > > > > > This is good but it would be better to explain that Landlock doesn't > > > currently control abstract unix sockets and that it would make sense for > > > a sandbox. > > > > > > > > > > > > > > For a landlocked process to be allowed to connect to a target process, it > > > > must have a subset of the target process’s rules (the connecting socket > > > > must be in a sub-domain of the listening socket). This patch adds a new > > > > LSM hook for connect function in unix socket with the related access rights. > > > > > > Because of compatibility reasons, and because Landlock should be > > > flexible, we need to extend the user space interface. As explained in > > > the GitHub issue, we need to add a new "scoped" field to the > > > landlock_ruleset_attr struct. This field will optionally contain a > > > LANDLOCK_RULESET_SCOPED_ABSTRACT_UNIX_SOCKET flag to specify that this > > > ruleset will deny any connection from within the sandbox to its parents > > > (i.e. any parent sandbox or not-sandboxed processes). > > > Thanks for the feedback. Here is what I understood, please correct me if > > I am wrong. First, I should add another field to the > > landlock_ruleset_attr (a field like handled_access_net, but for the unix > > sockets) with a flag LANDLOCK_ACCESS_UNIX_CONNECT (it is a flag like > > LANDLOCK_ACCESS_NET_CONNECT_TCP but fot the unix sockets connect). > > That was the initial idea, but after thinking more about it and talking > with some users, I now think we can get a more generic interface. > > Because unix sockets, signals, and other IPCs are fully controlled by > the kernel (contrary to inet sockets that get out of the system), we can > add ingress and egress control according to the source and the > destination. > > To control the direction we could add an > LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT_RECEIVE and a > LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT_SEND rights (these names are a bit > long but at least explicit). To control the source and destination, it > makes sense to use Landlock domain (i.e. sandboxes): > LANDLOCK_DOMAIN_HIERARCHY_PARENT, LANDLOCK_DOMAIN_HIERARCHY_SELF, and > LANDLOCK_DOMAIN_HIERARCHY_CHILD. This could be used by extending the > landlock_ruleset_attr type and adding a new > landlock_domain_hierarchy_attr type: > > struct landlock_ruleset_attr ruleset_attr = { > .handled_access_dom = LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT_RECEIVE | \ > LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT_SEND, > } > > // Allows sending data to and receiving data from processes in the same > // domain or a child domain, through abstract unix sockets. > struct landlock_domain_hierarchy_attr dom_attr = { > .allowed_access = LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT_RECEIVE | \ > LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT_SEND, > .relationship = LANDLOCK_DOMAIN_HIERARCHY_SELF | \ > LANDLOCK_DOMAIN_HIERARCHY_CHILD, > }; > > It should also work with other kind of IPCs: > * LANDLOCK_ACCESS_DOM_UNIX_PATHNAME_RECEIVE/SEND (signal) > * LANDLOCK_ACCESS_DOM_SIGNAL_RECEIVE/SEND (signal) > * LANDLOCK_ACCESS_DOM_XSI_RECEIVE/SEND (XSI message queue) > * LANDLOCK_ACCESS_DOM_MQ_RECEIVE/SEND (POSIX message queue) > * LANDLOCK_ACCESS_DOM_PTRACE_RECEIVE/SEND (ptrace, which would be > limited) > > What do you think? Indeed, in the case of abstract Unix sockets, both parties can send and receive data when a connection is established. Therefore, we can define a single LANDLOCK_ACCESS_DOM_UNIX_ABSTRACT to represent the right to share data, regardless of direction. However, we should still retain LANDLOCK_DOMAIN_HIERARCHY for SELF, PARENT, and CHILD, as the source and destination are important. As you said, I believe we should have receive and send rights for another kind of IPCs (which will be used for landlock#8 issue)
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