SEND(4) FreeBSD Kernel Interfaces Manual SEND(4)
NAME
send - Kernel side support for Secure Neighbor Discovery (SeND)
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet6/send.h>
int
socket(PF_INET6, SOCK_RAW, IPPROTO_SEND);
To load the driver as a module at boot time, place the following line in
loader.conf(5):
send_load="YES"
DESCRIPTION
IPv6 nodes use the Neighbor Discovery Protocol (NDP) to discover other
nodes on the link, to determine their link-layer addresses to find
routers, and to maintain reachability information about the paths to
active members. NDP is vulnerable to various attacks [RFC3756]. Secure
Neighbor Discovery is a set of extensions to NDP that counter threats to
NDP [RFC3971].
Kernel side support for SeND consists of a kernel module with hooks that
divert relevant packets (Neighbor Solicitations, Neighbor Advertisements,
Router Solicitations, Router Advertisements and Redirects) from the NDP
stack, send them to user space on a dedicated socket and reinject them
back for further processing. Hooks are triggered only if the send module
is loaded.
The native SeND socket is similar to a raw IP socket, but with its own,
internal pseudo-protocol (IPPROTO_SEND). Struct sockaddr_send is defined
in <netinet6/send.h>. It defines the total length of the structure, the
address family, packet's incoming or outgoing direction from the
interface's point of view, and the interface index.
struct sockaddr_send {
unsigned char send_len; /* total length */
sa_family_t send_family; /* address family */
int send_direction;
int send_ifidx;
char send_zero[8];
};
The address family is always AF_INET6. The send_direction variable
denotes the direction of the packet from the interface's point of view
and has either the value SND_IN or SND_OUT. The send_ifidx variable is
the interface index of the receiving or sending interface. The send_zero
variable is padding and must always be zero.
In case that no user space application is connected to the send socket,
processing continues normally as if the module was not loaded.
INPUT HOOK
The input hook is named after the input path of the incoming or outgoing
NDP packets, on the way from the wire, through the nd6 stack, to user
space. Relevant packets are identified by adding an mbuf_tag (see
mbuf_tags(9)) to the mbuf(9), if the send module is loaded. It is then
passed on to the kernel-userland interface for either cryptographic
protection or validation by the SeND application. The hook takes an
argument that describes the direction of the packet, both in case of
incoming and outgoing packets. SND_IN is the direction of the incoming
packets that are usually protected by the SeND options and then sent to
user space for cryptographic validation. SND_OUT is the outgoing
direction. It describes both reply and locally originated outgoing
packets that are sent to user space for the addition of SeND options.
INCOMING PACKETS
The incoming ND packet from the wire:
kernelspace ( userspace
)
incoming SeND/ND packet (
| )
v ( SND_IN ) (
icmp6_input() -> send_input_hook ---> send socket ----+
: ) |
: # # ( |
normal : # # ) v
processing : # send.ko # ( SeND application
path : # # ) |
: # # ( |
v ) |
icmp6/nd6_??_input() <- protocol switch <--- send socket <---+
| structure (IPPPROTO_SEND) )
| ( SND_IN ) (
v )
continue normal ND processing (
OUTGOING PACKETS
Outgoing ND packet (reply or locally triggered):
kernelspace ( userspace
)
nd6_na_input() (
+PACKET_TAG_ND_OUTGOING )
| )
| outgoing packet (
| | )
| v (
| icmp6_redirect_output() )
| nd6_ns_output() (
| nd6_na_output() )
| +PACKET_TAG_ND_OUTGOING (
| | )
| +-----------<- rip6_output() <----------)----- rtsol/rtadvd/..
| | +PACKET_TAG_ND_OUTGOING (
| v )
| ip6_output() (
| | )
+-------->-+ (
| )
v ( SND_OUT ) (
nd6_output_lle() -> send_input_hook ---> send socket ----+
-PACKET_TAG_ND_OUTGOING ) |
: # # ( |
normal : # # ) v
processing : # send.ko # ( SeND application
path : # # ) |
: # # ( |
v ) |
(*ifp->if_output)() <- protocol switch <--- send socket <---+)() <- protocol switch <--- send socket <---+
| structure (IPPPROTO_SEND) )
| ( SND_OUT ) (
v )
continue with normal packet output (
ERRORS
A socket operation may fail with one of the following errors returned:
[EEXIST] Another user space SeND application is bound to the
socket.
[ENOBUFS] Shortage of space to receive the incoming (SeND-
protected) or outgoing (SeND-validated) packet from
the SeND application.
[ENOSYS] A packet received from user space and passed to the
NDP stack for further processing is neither Neighbor
Solicitation, Neighbor Advertisement, Router
Solicitation, Router Advertisement nor Redirect.
[ENOENT] Occurs if interface output routines fail to send the
packet out of the interface.
SEE ALSO
recvfrom(2), sendto(2), socket(2), loader.conf(5)
HISTORY
The send module first appeared in FreeBSD 9.0.
AUTHORS
Ana Kukec <anchie@FreeBSD.org>, University of Zagreb
BUGS
Due to the lack of NDP locking, it is currently not possible to unload
the send module.
FreeBSD 13.1-RELEASE-p6 September 19, 2010 FreeBSD 13.1-RELEASE-p6
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