NAME
"Socket::Packet" - interface to Linux's "PF_PACKET" socket family
SYNOPSIS
use Socket qw( SOCK_RAW );
use Socket::Packet qw(
PF_PACKET
ETHPALL
pack_sockaddr_ll unpack_sockaddr_ll
);
socket( my $sock, PF_PACKET, SOCK_RAW, 0 )
or die "Cannot socket() - $!\n";
bind( $sock, pack_sockaddr_ll( ETHPALL, 0, 0, 0, "" ) )
or die "Cannot bind() - $!\n";
while( my $addr = recv( $sock, my $packet, 8192, 0 ) ) {
my ( $proto, $ifindex, $hatype, $pkttype, $addr )
= unpack_sockaddr_ll( $addr );
...
}
DESCRIPTION
To quote packet(7):
Packet sockets are used to receive or send raw packets at the device driver
(OSI Layer 2) level. They allow the user to implement protocol modules in
user space on top of the physical layer.
Sockets in the "PF_PACKET" family get direct link-level access to the underlying hardware (i.e. Ethernet or similar). They are usually used to implement packet capturing, or sending of specially-constructed packets or to implement protocols the underlying kernel does not recognise.
The use of "PF_PACKET" sockets is usually restricted to privileged users only.
This module also provides various other support functions which wrap "ioctl()"s or socket options. This includes support for "PACKET_RX_RING", the high-performance zero-copy packet receive buffering, if the underlying platform supports it.
CONSTANTS
The following constants are exported
PF_PACKET
The packet family (for "socket()" calls)
AF_PACKET
The address family
PACKET_HOST
This packet is inbound unicast for this host.
PACKET_BROADCAST
This packet is inbound broadcast.
PACKET_MULTICAST
This packet is inbound multicast.
PACKET_OTHERHOST
This packet is inbound unicast for another host.
PACKET_OUTGOING
This packet is outbound.
ETHPALL
Pseudo-protocol number to capture all protocols.
SOL_PACKET
Socket option level for "getsockopt" and "setsockopt".
SOCKET OPTIONS
The following constants define socket options
PACKET_STATISTICS (get; struct tpacket_stats)
Packet received and drop counters.
PACKET_ORIGDEV (get or set; int)
Received packets will indicate the originally-received device,
rather than the apparent one. This mainly relates to Ethernet
bonding or VLANs.
This socket option is optional, and may not be provided on all
platforms.
PACKET_ADD_MEMBERSHIP (set; struct packet_mreq) PACKET_DROP_MEMBERSHIP (set; struct packet_mreq)
Membership of multicast or broadcast groups, or set promiscuous
mode.
The "packet_mreq" "type" field should be one of the following:
PACKET_MR_MULTICAST
A multicast group
PACKET_MR_PROMISC
Set or clear the promiscuous flag; the address is ignored
PACKET_MR_ALLMULTI
Set or clear the allmulti flag; the address is ignored
FUNCTIONS
The following pair of functions operate on "AF_PACKET" address structures. The meanings of the parameters are:
protocol
An ethertype protocol number. When using an address with
"bind()", the constant "ETHPALL" can be used instead, to
capture any protocol. The "pack_sockaddr_ll()" and
"unpack_sockaddr_ll()" functions byte-swap this value to or from
network endian order.
ifindex The index number of the interface on which the packet was sent
or received. When using an address with "bind()", the value 0
can be used instead, to watch all interfaces.
hatype The hardware ARP type of hardware address.
pkttype The type of the packet; indicates if it was sent or received.
Will be one of the "PACKET_*" values.
addr The underlying hardware address, in the type given by "hatype".
$a = pack_sockaddr_ll( $protocol, $ifindex, $hatype, $pkttype, $addr ) Returns a "sockaddr_ll" structure with the fields packed into it.
( $protocol, $ifindex, $hatype, $pkttype, $addr ) = unpack_sockaddr_ll( $a ) Takes a "sockaddr_ll" structure and returns the unpacked fields from it.
$mreq = pack_packet_mreq( $ifindex, $type, $addr ) Returns a "packet_mreq" structure with the fields packed into it.
( $ifindex, $type, $addr ) = unpack_packet_mreq( $mreq ) Takes a "packet_mreq" structure and returns the unpacked fields from it.
( $packets, $drops ) = unpack_tpacket_stats( $stats ) Takes a "tpacket_stats" structure from the "PACKET_STATISTICS" sockopt and returns the unpacked fields from it.
$time = siocgstamp( $sock )
( $sec, $usec ) = siocgstamp( $sock )
Returns the timestamp of the last received packet on the socket (as
obtained by the "SIOCGSTAMP" "ioctl"). In scalar context, returns a
single floating-point value in UNIX epoch seconds. In list context,
returns the number of seconds, and the number of microseconds.
$time = siocgstampns( $sock )
( $sec, $nsec ) = siocgstampns( $sock )
Returns the nanosecond-precise timestamp of the last received packet on
the socket (as obtained by the "SIOCGSTAMPNS" "ioctl"). In scalar
context, returns a single floating-point value in UNIX epoch seconds. In
list context, returns the number of seconds, and the number of
nanoseconds.
$ifindex = siocgifindex( $sock, $ifname ) Returns the "ifindex" of the interface with the given name if one exists, or "undef" if not. $sock does not need to be a "PF_PACKET" socket, any socket handle will do.
$ifname = siocgifname( $sock, $ifindex ) Returns the "ifname" of the interface at the given index if one exists, or "undef" if not. $sock does not need to be a "PF_PACKET" socket, any socket handle will do.
( $addr, $len ) = recv_len( $sock, $buffer, $maxlen, $flags ) Similar to Perl's "recv" builtin, except it returns the packet length as an explict return value. This may be useful if $flags contains the "MSG_TRUNC" flag, obtaining the true length of the packet on the wire, even if this is longer than the data written in the buffer.
RING-BUFFER FUNCTIONS
The following functions operate on the high-performance memory-mapped buffer feature of "PF_PACKET", allowing efficient packet-capture applications to share a buffer with the kernel directly, avoiding the need for per-packet system calls to "recv()" (and possibly "ioctl()" to obtain the timestamp).
The ring-buffer is optional, and may not be implemented on all platforms. If it is not implemented, then all the following functions will die with an error message.
$size = setup_rx_ring( $sock, $frame_size, $frame_nr, $block_size ) Sets up the ring-buffer on the socket. The buffer will store $frame_nr frames of up to $frame_size bytes each (including metadata headers), and will be split in the kernel in blocks of $block_size bytes. $block_size should be a power of 2, at minimum, 4KiB.
If successful, the overall size of the buffer in bytes is returned. If not, "undef" is returned, and $! will hold the error value.
$status = get_ring_frame_status( $sock ) Returns the frame status of the next frame in the ring.
The following constants are defined for the status:
TP_STATUS_KERNEL
This frame belongs to the kernel and userland should not touch
it.
TP_STATUS_USER
This frame belongs to userland and the kernel will not modify
it.
TP_STATUS_LOSING
Bitwise-or'ed with the status if packet loss has occurred since
the previous frame.
$len = get_ring_frame( $sock, $buffer, \%info ) If the next frame is ready for userland, fills in keys of the %info hash with its metadata, sets $buffer to its contents, and return the length of the data. The $buffer variable has its string backing buffer aliased, rather than the buffer copied into, for performance. The caller should not modify the variable, nor attempt to access it after the socket has been closed.
If the frame is not yet ready, this function returns undef.
The following fields are returned:
tp_status
The status of the frame; see "get_ring_frame_status()"
tp_len The length of the packet on the wire, in bytes
tp_snaplen
The length of the packet captured and stored in the buffer, in
bytes. This may be shorter than "tp_len" if, for example, a
filter is set on the socket that truncated the packet.
tp_sec
tp_nsec The seconds and nanoseconds fields of the timestamp. If the
underlying platform does not support "TPACKET_V2", then this
field will only have a resolution of microseconds; i.e. it will
be a whole multiple of 1000.
tp_vlan_tci
VLAN information about the packet, if the underlying platform
supports "TPACKET_V2". If this is not supported, the key will
not be present in the hash
sll_protocol
sll_ifindex
sll_hatype
sll_pkttype
sll_addr
Fields from the "struct sockaddr_ll"; see above for more detail
clear_ring_frame( $sock )
Clears the status of current frame to hand it back to the kernel and
moves on to the next.
SEE ALSO
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>