netlink_linux.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Netlink sockets and messages
     6  
     7  package syscall
     8  
     9  import "unsafe"
    10  
    11  // Round the length of a netlink message up to align it properly.
    12  func nlmAlignOf(msglen int) int {
    13  	return (msglen + NLMSG_ALIGNTO - 1) & ^(NLMSG_ALIGNTO - 1)
    14  }
    15  
    16  // Round the length of a netlink route attribute up to align it
    17  // properly.
    18  func rtaAlignOf(attrlen int) int {
    19  	return (attrlen + RTA_ALIGNTO - 1) & ^(RTA_ALIGNTO - 1)
    20  }
    21  
    22  // NetlinkRouteRequest represents a request message to receive routing
    23  // and link states from the kernel.
    24  type NetlinkRouteRequest struct {
    25  	Header NlMsghdr
    26  	Data   RtGenmsg
    27  }
    28  
    29  func (rr *NetlinkRouteRequest) toWireFormat() []byte {
    30  	b := make([]byte, rr.Header.Len)
    31  	*(*uint32)(unsafe.Pointer(&b[0:4][0])) = rr.Header.Len
    32  	*(*uint16)(unsafe.Pointer(&b[4:6][0])) = rr.Header.Type
    33  	*(*uint16)(unsafe.Pointer(&b[6:8][0])) = rr.Header.Flags
    34  	*(*uint32)(unsafe.Pointer(&b[8:12][0])) = rr.Header.Seq
    35  	*(*uint32)(unsafe.Pointer(&b[12:16][0])) = rr.Header.Pid
    36  	b[16] = byte(rr.Data.Family)
    37  	return b
    38  }
    39  
    40  func newNetlinkRouteRequest(proto, seq, family int) []byte {
    41  	rr := &NetlinkRouteRequest{}
    42  	rr.Header.Len = uint32(NLMSG_HDRLEN + SizeofRtGenmsg)
    43  	rr.Header.Type = uint16(proto)
    44  	rr.Header.Flags = NLM_F_DUMP | NLM_F_REQUEST
    45  	rr.Header.Seq = uint32(seq)
    46  	rr.Data.Family = uint8(family)
    47  	return rr.toWireFormat()
    48  }
    49  
    50  // NetlinkRIB returns routing information base, as known as RIB, which
    51  // consists of network facility information, states and parameters.
    52  func NetlinkRIB(proto, family int) ([]byte, error) {
    53  	s, err := cloexecSocket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)
    54  	if err != nil {
    55  		return nil, err
    56  	}
    57  	defer Close(s)
    58  	sa := &SockaddrNetlink{Family: AF_NETLINK}
    59  	if err := Bind(s, sa); err != nil {
    60  		return nil, err
    61  	}
    62  	wb := newNetlinkRouteRequest(proto, 1, family)
    63  	if err := Sendto(s, wb, 0, sa); err != nil {
    64  		return nil, err
    65  	}
    66  	lsa, err := Getsockname(s)
    67  	if err != nil {
    68  		return nil, err
    69  	}
    70  	lsanl, ok := lsa.(*SockaddrNetlink)
    71  	if !ok {
    72  		return nil, EINVAL
    73  	}
    74  	var tab []byte
    75  	rbNew := make([]byte, Getpagesize())
    76  done:
    77  	for {
    78  		rb := rbNew
    79  		nr, _, err := Recvfrom(s, rb, 0)
    80  		if err != nil {
    81  			return nil, err
    82  		}
    83  		if nr < NLMSG_HDRLEN {
    84  			return nil, EINVAL
    85  		}
    86  		rb = rb[:nr]
    87  		tab = append(tab, rb...)
    88  		msgs, err := ParseNetlinkMessage(rb)
    89  		if err != nil {
    90  			return nil, err
    91  		}
    92  		for _, m := range msgs {
    93  			if m.Header.Seq != 1 || m.Header.Pid != lsanl.Pid {
    94  				return nil, EINVAL
    95  			}
    96  			if m.Header.Type == NLMSG_DONE {
    97  				break done
    98  			}
    99  			if m.Header.Type == NLMSG_ERROR {
   100  				return nil, EINVAL
   101  			}
   102  		}
   103  	}
   104  	return tab, nil
   105  }
   106  
   107  // NetlinkMessage represents a netlink message.
   108  type NetlinkMessage struct {
   109  	Header NlMsghdr
   110  	Data   []byte
   111  }
   112  
   113  // ParseNetlinkMessage parses b as an array of netlink messages and
   114  // returns the slice containing the NetlinkMessage structures.
   115  func ParseNetlinkMessage(b []byte) ([]NetlinkMessage, error) {
   116  	var msgs []NetlinkMessage
   117  	for len(b) >= NLMSG_HDRLEN {
   118  		h, dbuf, dlen, err := netlinkMessageHeaderAndData(b)
   119  		if err != nil {
   120  			return nil, err
   121  		}
   122  		m := NetlinkMessage{Header: *h, Data: dbuf[:int(h.Len)-NLMSG_HDRLEN]}
   123  		msgs = append(msgs, m)
   124  		b = b[dlen:]
   125  	}
   126  	return msgs, nil
   127  }
   128  
   129  func netlinkMessageHeaderAndData(b []byte) (*NlMsghdr, []byte, int, error) {
   130  	h := (*NlMsghdr)(unsafe.Pointer(&b[0]))
   131  	l := nlmAlignOf(int(h.Len))
   132  	if int(h.Len) < NLMSG_HDRLEN || l > len(b) {
   133  		return nil, nil, 0, EINVAL
   134  	}
   135  	return h, b[NLMSG_HDRLEN:], l, nil
   136  }
   137  
   138  // NetlinkRouteAttr represents a netlink route attribute.
   139  type NetlinkRouteAttr struct {
   140  	Attr  RtAttr
   141  	Value []byte
   142  }
   143  
   144  // ParseNetlinkRouteAttr parses m's payload as an array of netlink
   145  // route attributes and returns the slice containing the
   146  // NetlinkRouteAttr structures.
   147  func ParseNetlinkRouteAttr(m *NetlinkMessage) ([]NetlinkRouteAttr, error) {
   148  	var b []byte
   149  	switch m.Header.Type {
   150  	case RTM_NEWLINK, RTM_DELLINK:
   151  		b = m.Data[SizeofIfInfomsg:]
   152  	case RTM_NEWADDR, RTM_DELADDR:
   153  		b = m.Data[SizeofIfAddrmsg:]
   154  	case RTM_NEWROUTE, RTM_DELROUTE:
   155  		b = m.Data[SizeofRtMsg:]
   156  	default:
   157  		return nil, EINVAL
   158  	}
   159  	var attrs []NetlinkRouteAttr
   160  	for len(b) >= SizeofRtAttr {
   161  		a, vbuf, alen, err := netlinkRouteAttrAndValue(b)
   162  		if err != nil {
   163  			return nil, err
   164  		}
   165  		ra := NetlinkRouteAttr{Attr: *a, Value: vbuf[:int(a.Len)-SizeofRtAttr]}
   166  		attrs = append(attrs, ra)
   167  		b = b[alen:]
   168  	}
   169  	return attrs, nil
   170  }
   171  
   172  func netlinkRouteAttrAndValue(b []byte) (*RtAttr, []byte, int, error) {
   173  	a := (*RtAttr)(unsafe.Pointer(&b[0]))
   174  	if int(a.Len) < SizeofRtAttr || int(a.Len) > len(b) {
   175  		return nil, nil, 0, EINVAL
   176  	}
   177  	return a, b[SizeofRtAttr:], rtaAlignOf(int(a.Len)), nil
   178  }
   179
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