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conn_linux.go
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conn_linux.go
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//go:build linux
// +build linux
package netlink
import (
"context"
"os"
"syscall"
"time"
"unsafe"
"github.com/mdlayher/socket"
"golang.org/x/net/bpf"
"golang.org/x/sys/unix"
)
var _ Socket = &conn{}
// A conn is the Linux implementation of a netlink sockets connection.
type conn struct {
s *socket.Conn
}
// dial is the entry point for Dial. dial opens a netlink socket using
// system calls, and returns its PID.
func dial(family int, config *Config) (*conn, uint32, error) {
if config == nil {
config = &Config{}
}
// Prepare the netlink socket.
s, err := socket.Socket(
unix.AF_NETLINK,
unix.SOCK_RAW,
family,
"netlink",
&socket.Config{NetNS: config.NetNS},
)
if err != nil {
return nil, 0, err
}
return newConn(s, config)
}
// newConn binds a connection to netlink using the input *socket.Conn.
func newConn(s *socket.Conn, config *Config) (*conn, uint32, error) {
if config == nil {
config = &Config{}
}
addr := &unix.SockaddrNetlink{
Family: unix.AF_NETLINK,
Groups: config.Groups,
Pid: config.PID,
}
// Socket must be closed in the event of any system call errors, to avoid
// leaking file descriptors.
if err := s.Bind(addr); err != nil {
_ = s.Close()
return nil, 0, err
}
sa, err := s.Getsockname()
if err != nil {
_ = s.Close()
return nil, 0, err
}
c := &conn{s: s}
if config.Strict {
// The caller has requested the strict option set. Historically we have
// recommended checking for ENOPROTOOPT if the kernel does not support
// the option in question, but that may result in a silent failure and
// unexpected behavior for the user.
//
// Treat any error here as a fatal error, and require the caller to deal
// with it.
for _, o := range []ConnOption{ExtendedAcknowledge, GetStrictCheck} {
if err := c.SetOption(o, true); err != nil {
_ = c.Close()
return nil, 0, err
}
}
}
return c, sa.(*unix.SockaddrNetlink).Pid, nil
}
// SendMessages serializes multiple Messages and sends them to netlink.
func (c *conn) SendMessages(messages []Message) error {
var buf []byte
for _, m := range messages {
b, err := m.MarshalBinary()
if err != nil {
return err
}
buf = append(buf, b...)
}
sa := &unix.SockaddrNetlink{Family: unix.AF_NETLINK}
_, err := c.s.Sendmsg(context.Background(), buf, nil, sa, 0)
return err
}
// Send sends a single Message to netlink.
func (c *conn) Send(m Message) error {
b, err := m.MarshalBinary()
if err != nil {
return err
}
sa := &unix.SockaddrNetlink{Family: unix.AF_NETLINK}
_, err = c.s.Sendmsg(context.Background(), b, nil, sa, 0)
return err
}
// Receive receives one or more Messages from netlink.
func (c *conn) Receive() ([]Message, error) {
b := make([]byte, os.Getpagesize())
for {
// Peek at the buffer to see how many bytes are available.
//
// TODO(mdlayher): deal with OOB message data if available, such as
// when PacketInfo ConnOption is true.
n, _, _, _, err := c.s.Recvmsg(context.Background(), b, nil, unix.MSG_PEEK)
if err != nil {
return nil, err
}
// Break when we can read all messages
if n < len(b) {
break
}
// Double in size if not enough bytes
b = make([]byte, len(b)*2)
}
// Read out all available messages
n, _, _, _, err := c.s.Recvmsg(context.Background(), b, nil, 0)
if err != nil {
return nil, err
}
raw, err := syscall.ParseNetlinkMessage(b[:nlmsgAlign(n)])
if err != nil {
return nil, err
}
msgs := make([]Message, 0, len(raw))
for _, r := range raw {
m := Message{
Header: sysToHeader(r.Header),
Data: r.Data,
}
msgs = append(msgs, m)
}
return msgs, nil
}
// Close closes the connection.
func (c *conn) Close() error { return c.s.Close() }
// JoinGroup joins a multicast group by ID.
func (c *conn) JoinGroup(group uint32) error {
return c.s.SetsockoptInt(unix.SOL_NETLINK, unix.NETLINK_ADD_MEMBERSHIP, int(group))
}
// LeaveGroup leaves a multicast group by ID.
func (c *conn) LeaveGroup(group uint32) error {
return c.s.SetsockoptInt(unix.SOL_NETLINK, unix.NETLINK_DROP_MEMBERSHIP, int(group))
}
// SetBPF attaches an assembled BPF program to a conn.
func (c *conn) SetBPF(filter []bpf.RawInstruction) error { return c.s.SetBPF(filter) }
// RemoveBPF removes a BPF filter from a conn.
func (c *conn) RemoveBPF() error { return c.s.RemoveBPF() }
// SetOption enables or disables a netlink socket option for the Conn.
func (c *conn) SetOption(option ConnOption, enable bool) error {
o, ok := linuxOption(option)
if !ok {
// Return the typical Linux error for an unknown ConnOption.
return os.NewSyscallError("setsockopt", unix.ENOPROTOOPT)
}
var v int
if enable {
v = 1
}
return c.s.SetsockoptInt(unix.SOL_NETLINK, o, v)
}
func (c *conn) SetDeadline(t time.Time) error { return c.s.SetDeadline(t) }
func (c *conn) SetReadDeadline(t time.Time) error { return c.s.SetReadDeadline(t) }
func (c *conn) SetWriteDeadline(t time.Time) error { return c.s.SetWriteDeadline(t) }
// SetReadBuffer sets the size of the operating system's receive buffer
// associated with the Conn.
func (c *conn) SetReadBuffer(bytes int) error { return c.s.SetReadBuffer(bytes) }
// SetReadBuffer sets the size of the operating system's transmit buffer
// associated with the Conn.
func (c *conn) SetWriteBuffer(bytes int) error { return c.s.SetWriteBuffer(bytes) }
// SyscallConn returns a raw network connection.
func (c *conn) SyscallConn() (syscall.RawConn, error) { return c.s.SyscallConn() }
// linuxOption converts a ConnOption to its Linux value.
func linuxOption(o ConnOption) (int, bool) {
switch o {
case PacketInfo:
return unix.NETLINK_PKTINFO, true
case BroadcastError:
return unix.NETLINK_BROADCAST_ERROR, true
case NoENOBUFS:
return unix.NETLINK_NO_ENOBUFS, true
case ListenAllNSID:
return unix.NETLINK_LISTEN_ALL_NSID, true
case CapAcknowledge:
return unix.NETLINK_CAP_ACK, true
case ExtendedAcknowledge:
return unix.NETLINK_EXT_ACK, true
case GetStrictCheck:
return unix.NETLINK_GET_STRICT_CHK, true
default:
return 0, false
}
}
// sysToHeader converts a syscall.NlMsghdr to a Header.
func sysToHeader(r syscall.NlMsghdr) Header {
// NB: the memory layout of Header and syscall.NlMsgHdr must be
// exactly the same for this unsafe cast to work
return *(*Header)(unsafe.Pointer(&r))
}
// newError converts an error number from netlink into the appropriate
// system call error for Linux.
func newError(errno int) error {
return syscall.Errno(errno)
}