directory, and an inode can be referenced by multiple file names thanks to
(hard) links. Being able to unlink a file only has a direct impact on the
directory, not the unlinked inode. This is the reason why
-`LANDLOCK_ACCESS_FS_REMOVE_FILE` or `LANDLOCK_ACCESS_FS_REFER` are not allowed
-to be tied to files but only to directories.
+``LANDLOCK_ACCESS_FS_REMOVE_FILE`` or ``LANDLOCK_ACCESS_FS_REFER`` are not
+allowed to be tied to files but only to directories.
Tests
=====
using. To avoid binary enforcement (i.e. either all security features or
none), we can leverage a dedicated Landlock command to get the current version
of the Landlock ABI and adapt the handled accesses. Let's check if we should
-remove the `LANDLOCK_ACCESS_FS_REFER` access right which is only supported
+remove the ``LANDLOCK_ACCESS_FS_REFER`` access right which is only supported
starting with the second version of the ABI.
.. code-block:: c
It may also be required to create rules following the same logic as explained
for the ruleset creation, by filtering access rights according to the Landlock
ABI version. In this example, this is not required because
-`LANDLOCK_ACCESS_FS_REFER` is not allowed by any rule.
+``LANDLOCK_ACCESS_FS_REFER`` is not allowed by any rule.
We now have a ruleset with one rule allowing read access to ``/usr`` while
denying all other handled accesses for the filesystem. The next step is to
}
close(ruleset_fd);
-If the `landlock_restrict_self` system call succeeds, the current thread is now
-restricted and this policy will be enforced on all its subsequently created
+If the ``landlock_restrict_self`` system call succeeds, the current thread is
+now restricted and this policy will be enforced on all its subsequently created
children as well. Once a thread is landlocked, there is no way to remove its
security policy; only adding more restrictions is allowed. These threads are
now in a new Landlock domain, merge of their parent one (if any) with the new
relevant when we want to allow linking or renaming. Indeed, having consistent
access rights per directory enables to change the location of such directory
without relying on the destination directory access rights (except those that
-are required for this operation, see `LANDLOCK_ACCESS_FS_REFER` documentation).
+are required for this operation, see ``LANDLOCK_ACCESS_FS_REFER``
+documentation).
Having self-sufficient hierarchies also helps to tighten the required access
rights to the minimal set of data. This also helps avoid sinkhole directories,
i.e. directories where data can be linked to but not linked from. However,
Landlock is designed to be compatible with past and future versions of the
kernel. This is achieved thanks to the system call attributes and the
-associated bitflags, particularly the ruleset's `handled_access_fs`. Making
+associated bitflags, particularly the ruleset's ``handled_access_fs``. Making
handled access right explicit enables the kernel and user space to have a clear
contract with each other. This is required to make sure sandboxing will not
get stricter with a system update, which could break applications.
escalations through renaming or linking, and for the sake of simplicity,
Landlock previously limited linking and renaming to the same directory.
Starting with the Landlock ABI version 2, it is now possible to securely
-control renaming and linking thanks to the new `LANDLOCK_ACCESS_FS_REFER`
+control renaming and linking thanks to the new ``LANDLOCK_ACCESS_FS_REFER``
access right.
.. _kernel_support:
==============
Landlock was first introduced in Linux 5.13 but it must be configured at build
-time with `CONFIG_SECURITY_LANDLOCK=y`. Landlock must also be enabled at boot
+time with ``CONFIG_SECURITY_LANDLOCK=y``. Landlock must also be enabled at boot
time as the other security modules. The list of security modules enabled by
-default is set with `CONFIG_LSM`. The kernel configuration should then
-contains `CONFIG_LSM=landlock,[...]` with `[...]` as the list of other
+default is set with ``CONFIG_LSM``. The kernel configuration should then
+contains ``CONFIG_LSM=landlock,[...]`` with ``[...]`` as the list of other
potentially useful security modules for the running system (see the
-`CONFIG_LSM` help).
+``CONFIG_LSM`` help).
-If the running kernel does not have `landlock` in `CONFIG_LSM`, then we can
+If the running kernel does not have ``landlock`` in ``CONFIG_LSM``, then we can
still enable it by adding ``lsm=landlock,[...]`` to
Documentation/admin-guide/kernel-parameters.rst thanks to the bootloader
configuration.
* Landlock filesystem access rights that are not part of
* handled_access_fs are allowed. This is needed for backward
* compatibility reasons. One exception is the
- * LANDLOCK_ACCESS_FS_REFER access right, which is always implicitly
+ * %LANDLOCK_ACCESS_FS_REFER access right, which is always implicitly
* handled, but must still be explicitly handled to add new rules with
* this access right.
*/
* hierarchy must also always have the same or a superset of restrictions of
* the source hierarchy. If it is not the case, or if the domain doesn't
* handle this access right, such actions are denied by default with errno
- * set to EXDEV. Linking also requires a LANDLOCK_ACCESS_FS_MAKE_* access
- * right on the destination directory, and renaming also requires a
- * LANDLOCK_ACCESS_FS_REMOVE_* access right on the source's (file or
+ * set to ``EXDEV``. Linking also requires a ``LANDLOCK_ACCESS_FS_MAKE_*``
+ * access right on the destination directory, and renaming also requires a
+ * ``LANDLOCK_ACCESS_FS_REMOVE_*`` access right on the source's (file or
* directory) parent. Otherwise, such actions are denied with errno set to
- * EACCES. The EACCES errno prevails over EXDEV to let user space
+ * ``EACCES``. The ``EACCES`` errno prevails over ``EXDEV`` to let user space
* efficiently deal with an unrecoverable error.
*
* .. warning::
*
* Possible returned errors are:
*
- * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
- * - EINVAL: unknown @flags, or unknown access, or too small @size;
- * - E2BIG or EFAULT: @attr or @size inconsistencies;
- * - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
+ * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - %EINVAL: unknown @flags, or unknown access, or too small @size;
+ * - %E2BIG or %EFAULT: @attr or @size inconsistencies;
+ * - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
*/
SYSCALL_DEFINE3(landlock_create_ruleset,
const struct landlock_ruleset_attr __user *const, attr,
* @ruleset_fd: File descriptor tied to the ruleset that should be extended
* with the new rule.
* @rule_type: Identify the structure type pointed to by @rule_attr (only
- * LANDLOCK_RULE_PATH_BENEATH for now).
+ * %LANDLOCK_RULE_PATH_BENEATH for now).
* @rule_attr: Pointer to a rule (only of type &struct
* landlock_path_beneath_attr for now).
* @flags: Must be 0.
*
* Possible returned errors are:
*
- * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
- * - EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
+ * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - %EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
* &landlock_path_beneath_attr.allowed_access is not a subset of the
* ruleset handled accesses);
- * - ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access);
- * - EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
+ * - %ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access);
+ * - %EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
* member of @rule_attr is not a file descriptor as expected;
- * - EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
+ * - %EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
* @rule_attr is not the expected file descriptor type;
- * - EPERM: @ruleset_fd has no write access to the underlying ruleset;
- * - EFAULT: @rule_attr inconsistency.
+ * - %EPERM: @ruleset_fd has no write access to the underlying ruleset;
+ * - %EFAULT: @rule_attr inconsistency.
*/
SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
const enum landlock_rule_type, rule_type,
* @flags: Must be 0.
*
* This system call enables to enforce a Landlock ruleset on the current
- * thread. Enforcing a ruleset requires that the task has CAP_SYS_ADMIN in its
+ * thread. Enforcing a ruleset requires that the task has %CAP_SYS_ADMIN in its
* namespace or is running with no_new_privs. This avoids scenarios where
* unprivileged tasks can affect the behavior of privileged children.
*
* Possible returned errors are:
*
- * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
- * - EINVAL: @flags is not 0.
- * - EBADF: @ruleset_fd is not a file descriptor for the current thread;
- * - EBADFD: @ruleset_fd is not a ruleset file descriptor;
- * - EPERM: @ruleset_fd has no read access to the underlying ruleset, or the
+ * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - %EINVAL: @flags is not 0.
+ * - %EBADF: @ruleset_fd is not a file descriptor for the current thread;
+ * - %EBADFD: @ruleset_fd is not a ruleset file descriptor;
+ * - %EPERM: @ruleset_fd has no read access to the underlying ruleset, or the
* current thread is not running with no_new_privs, or it doesn't have
- * CAP_SYS_ADMIN in its namespace.
- * - E2BIG: The maximum number of stacked rulesets is reached for the current
+ * %CAP_SYS_ADMIN in its namespace.
+ * - %E2BIG: The maximum number of stacked rulesets is reached for the current
* thread.
*/
SYSCALL_DEFINE2(landlock_restrict_self, const int, ruleset_fd, const __u32,
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