[PATCH v8 4/4] Landlock: Document LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET and ABI versioning

[Mickaël Salaün]

On Thu, Aug 01, 2024 at 10:02:36PM -0600, Tahera Fahimi wrote:
> Introducing LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET as an IPC scoping
> mechanism in Landlock ABI version 6, and updating ruleset_attr,
> Landlock ABI version, and access rights code blocks based on that.
> 
> Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>
> ---
> v8:
> - Improving documentation by specifying differences between scoped and
>   non-scoped domains.
> - Adding review notes of version 7.
> - Update date
> v7:
> - Add "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" explanation to IPC scoping
>   section and updating ABI to version 6.
> - Adding "scoped" attribute to the Access rights section.
> - In current limitation, unnamed sockets are specified as sockets that
>   are not restricted.
> - Update date
> ---
>  Documentation/userspace-api/landlock.rst | 33 ++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
> index 07b63aec56fa..d602567b5139 100644
> --- a/Documentation/userspace-api/landlock.rst
> +++ b/Documentation/userspace-api/landlock.rst
> @@ -8,7 +8,7 @@ Landlock: unprivileged access control
>  =====================================
>  
>  :Author: Mickaël Salaün
> -:Date: April 2024
> +:Date: August 2024
>  
>  The goal of Landlock is to enable to restrict ambient rights (e.g. global
>  filesystem or network access) for a set of processes.  Because Landlock
> @@ -81,6 +81,8 @@ to be explicit about the denied-by-default access rights.
>          .handled_access_net =
>              LANDLOCK_ACCESS_NET_BIND_TCP |
>              LANDLOCK_ACCESS_NET_CONNECT_TCP,
> +        .scoped =
> +            LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET,
>      };
>  
>  Because we may not know on which kernel version an application will be
> @@ -119,6 +121,9 @@ version, and only use the available subset of access rights:
>      case 4:
>          /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
>          ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
> +    case 5:
> +        /* Removes LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */
> +        ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
>      }
>  
>  This enables to create an inclusive ruleset that will contain our rules.
> @@ -306,6 +311,23 @@ To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target
>  process, a sandboxed process should have a subset of the target process rules,
>  which means the tracee must be in a sub-domain of the tracer.
>  
> +IPC Scoping
> +-----------
> +
> +Similar to the implicit `Ptrace restrictions`_, we may want to further restrict
> +interactions between sandboxes. Each Landlock domain can be explicitly scoped
> +for a set of actions by specifying it on a ruleset. For example, if a sandboxed
> +process should not be able to :manpage:`connect(2)` to a non-sandboxed process
> +through abstract :manpage:`unix(7)` sockets, we can specify such restriction
> +with ``LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET``.
> +
> +A sandboxed process can connect to a non-sandboxed process when its domain is
> +not scoped. If a process's domain is scoped, it can only connect to processes in

...it can only connect to sockets created by proccesses in the same
scoped domain.

> +the same scoped domain.
> +
> +IPC scoping does not support Landlock rules, so if a domain is scoped, no rules
> +can be added to allow accessing to a resource outside of the scoped domain.
> +
>  Truncating files
>  ----------------
>  
> @@ -404,7 +426,7 @@ Access rights
>  -------------
>  
>  .. kernel-doc:: include/uapi/linux/landlock.h
> -    :identifiers: fs_access net_access
> +    :identifiers: fs_access net_access scope
>  
>  Creating a new ruleset
>  ----------------------
> @@ -541,6 +563,13 @@ earlier ABI.
>  Starting with the Landlock ABI version 5, it is possible to restrict the use of
>  :manpage:`ioctl(2)` using the new ``LANDLOCK_ACCESS_FS_IOCTL_DEV`` right.
>  
> +Abstract Unix sockets Restriction  (ABI < 6)

Let's follow the capitalization used by man pages: "UNIX" instead of
"Unix".

> +--------------------------------------------
> +
> +With ABI version 6, it is possible to restrict connection to an abstract Unix socket
> +through ``LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET``, thanks to the ``scoped`` ruleset
> +attribute.
> +
>  .. _kernel_support:
>  
>  Kernel support
> -- 
> 2.34.1
>