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landlock: Document LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET

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Introduce LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET as an IPC scoping
mechanism available since Landlock ABI version 6. Update ruleset_attr,
Landlock ABI version, and access rights code blocks based on that.

Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/ac75151861724c19ed62b500cfe497612d9a6607.1725494372.git.fahimitahera@gmail.com
[mic: Improve commit message and documentation, add a missing
fallthrough, reformat to 80 columns, improve some wording]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Tahera Fahimi 2024-09-04 18:14:02 -06:00 committed by Mickaël Salaün
parent 369b48b43a
commit dba40c7700
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1 changed files with 42 additions and 2 deletions
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44
Documentation/userspace-api/landlock.rst
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@ -8,7 +8,7 @@ Landlock: unprivileged access control
=====================================
:Author: Mickaël Salaün
:Date: July 2024
:Date: September 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_SCOPE_ABSTRACT_UNIX_SOCKET,
};
Because we may not know on which kernel version an application will be
@ -119,6 +121,10 @@ 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;
__attribute__((fallthrough));
case 5:
/* Removes LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET for ABI < 6 */
ruleset_attr.scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
}
This enables to create an inclusive ruleset that will contain our rules.
@ -306,6 +312,33 @@ 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_SCOPE_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 sockets
created by processes in the same scope.
A connected datagram socket behaves like a stream socket when its domain is
scoped, meaning if the domain is scoped after the socket is connected , it can
still :manpage:`send(2)` data just like a stream socket. However, in the same
scenario, a non-connected datagram socket cannot send data (with
:manpage:`sendto(2)`) outside its scope.
A process with a scoped domain can inherit a socket created by a non-scoped
process. The process cannot connect to this socket since it has a scoped
domain.
IPC scoping does not support exceptions, so if a domain is scoped, no rules can
be added to allow access to resources or processes outside of the scope.
Truncating files
----------------
@ -404,7 +437,7 @@ 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 +574,13 @@ 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 socket scoping (ABI < 6)
--------------------------------------
Starting with the Landlock ABI version 6, it is possible to restrict
connections to an abstract :manpage:`unix(7)` socket by setting
``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET`` to the ``scoped`` ruleset attribute.
.. _kernel_support:
Kernel support