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.

VERSIONS

       Landlock was added in Linux 5.13.

STANDARDS

       This system call is Linux-specific.

EXAMPLES

       See landlock(7).