NAME¶

landlock_add_rule - add a new Landlock rule to a 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_add_rule, int ruleset_fd,
            enum landlock_rule_type rule_type,
            const void *rule_attr, uint32_t flags);

DESCRIPTION¶

A Landlock rule describes an action on an object which the process intends to perform. A set of rules is aggregated in a ruleset, which can then restrict the thread enforcing it, and its future children.

The landlock_add_rule() system call adds a new Landlock rule to an existing ruleset. See landlock(7) for a global overview.

ruleset_fd is a Landlock ruleset file descriptor obtained with landlock_create_ruleset(2).

rule_type identifies the structure type pointed to by rule_attr. Currently, Linux supports the following rule_type values:

LANDLOCK_RULE_PATH_BENEATH

For these rules, the object is a file hierarchy, and the related filesystem actions are defined with filesystem access rights.

In this case, rule_attr points to the following structure:

struct landlock_path_beneath_attr {


    __u64 allowed_access;


    __s32 parent_fd;
} __attribute__((packed));
    

allowed_access contains a bitmask of allowed filesystem actions, which can be applied on the given parent_fd (see Filesystem actions in landlock(7)).

parent_fd is an opened file descriptor, preferably with the O_PATH flag, which identifies the parent directory of the file hierarchy or just a file.

LANDLOCK_RULE_NET_PORT

For these rules, the object is a TCP port, and the related actions are defined with network access rights.

In this case, rule_attr points to the following structure:

struct landlock_net_port_attr {


    __u64 allowed_access;


    __u64 port;
};
    

allowed_access contains a bitmask of allowed network actions, which can be applied on the given port.

port is the network port in host endianness.

It should be noted that port 0 passed to bind(2) will bind to an available port from the ephemeral port range. This can be configured in the /proc/sys/net/ipv4/ip_local_port_range sysctl (also used for IPv6).

A Landlock rule with port 0 and the LANDLOCK_ACCESS_NET_BIND_TCP right means that requesting to bind on port 0 is allowed and it will automatically translate to binding on the related port range.

flags must be 0.

RETURN VALUE¶

On success, landlock_add_rule() returns 0. On error, -1 is returned and errno is set to indicate the error.

ERRORS¶

landlock_add_rule() can fail for the following reasons:

EAFNOSUPPORT

rule_type is LANDLOCK_RULE_NET_PORT, but TCP is not supported by the running kernel.

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 rule_attr is not the expected file descriptor type.

EFAULT

rule_attr was not a valid address.

EINVAL

flags is not 0.

EINVAL

The rule accesses are inconsistent (i.e., rule_attr->allowed_access is not a subset of the ruleset handled accesses).

EINVAL

In struct landlock_path_beneath_attr, the rule accesses are not applicable to the file (i.e., some access rights in rule_attr->allowed_access are only applicable to directories, but rule_attr->parent_fd does not refer to a directory).

EINVAL

In struct landlock_net_port_attr, the port number is greater than 65535.

ENOMSG

Empty accesses (i.e., rule_attr->allowed_access is 0).

EOPNOTSUPP

Landlock is supported by the kernel but disabled at boot time.

EPERM

ruleset_fd has no write access to the underlying ruleset.

STANDARDS¶

Linux.

HISTORY¶

Linux 5.13.

EXAMPLES¶

See landlock(7).

SEE ALSO¶

landlock_create_ruleset(2), landlock_restrict_self(2), landlock(7)