#include <linux/landlock.h> /* Definition of LANDLOCK_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
int syscall(SYS_landlock_restrict_self, int ruleset_fd,
uint32_t flags);
A thread can be restricted with multiple rulesets that are then composed together to form the thread's Landlock domain. This can be seen as a stack of rulesets but it is implemented in a more efficient way. A domain can only be updated in such a way that the constraints of each past and future composed rulesets will restrict the thread and its future children for their entire life. It is then possible to gradually enforce tailored access control policies with multiple independent rulesets coming from different sources (e.g., init system configuration, user session policy, built-in application policy). However, most applications should only need one call to landlock_restrict_self() and they should avoid arbitrary numbers of such calls because of the composed rulesets limit. Instead, developers are encouraged to build a tailored ruleset thanks to multiple calls to landlock_add_rule(2).
In order to enforce a ruleset, either the caller must have the CAP_SYS_ADMIN capability in its user namespace, or the thread must already have the no_new_privs bit set. As for seccomp(2), this avoids scenarios where unprivileged processes can affect the behavior of privileged children (e.g., because of set-user-ID binaries). If that bit was not already set by an ancestor of this thread, the thread must make the following call:
ruleset_fd is a Landlock ruleset file descriptor obtained with landlock_create_ruleset(2) and fully populated with a set of calls to landlock_add_rule(2).