Ubuntu Manpage: landlock_restrict_self - enforce a Landlock ruleset

NAME

       landlock_restrict_self - enforce a Landlock ruleset

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #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);

DESCRIPTION

Once a Landlock ruleset is populated with the desired rules, the landlock_restrict_self() system call
enables enforcing this ruleset on the calling thread. See landlock(7) for a global overview.

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:

prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);

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).

flags must be 0.

RETURN VALUE

       On success, landlock_restrict_self() returns 0.

ERRORS

       landlock_restrict_self() can fail for the following reasons:

       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 calling thread is not running with
              no_new_privs, or it doesn't have the CAP_SYS_ADMIN in its user namespace.

       E2BIG  The maximum number of composed rulesets  is  reached  for  the  calling  thread.   This  limit  is
              currently 64.

STANDARDS

       Linux.

HISTORY

       Linux 5.13.

EXAMPLES

       See landlock(7).