/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2002-2018 OpenVPN Inc <sales@openvpn.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef FRAGMENT_H
#define FRAGMENT_H
/**
* @file
* Data Channel Fragmentation module header file.
*/
#ifdef ENABLE_FRAGMENT
/**
* @addtogroup fragmentation
* @{
*/
#include "common.h"
#include "buffer.h"
#include "interval.h"
#include "mtu.h"
#include "shaper.h"
#include "error.h"
#define N_FRAG_BUF 25
/**< Number of packet buffers for
* reassembling incoming fragmented
* packets. */
#define FRAG_TTL_SEC 10
/**< Time-to-live in seconds for a %fragment. */
#define FRAG_WAKEUP_INTERVAL 5
/**< Interval in seconds between calls to
* wakeup code. */
/**************************************************************************/
/**
* Structure for reassembling one incoming fragmented packet.
*/
struct fragment {
bool defined; /**< Whether reassembly is currently
* taking place in this structure. */
int max_frag_size; /**< Maximum size of each %fragment. */
#define FRAG_MAP_MASK 0xFFFFFFFF
/**< Mask for reassembly map. */
#define MAX_FRAGS 32 /**< Maximum number of fragments per packet. */
unsigned int map;
/**< Reassembly map for recording which
* fragments have been received.
*
* A bit array where each bit
* corresponds to a %fragment. A 1 bit
* in element n means that the %fragment
* n has been received. Needs to have
* at least \c MAX_FRAGS bits. */
time_t timestamp; /**< Timestamp for time-to-live purposes. */
struct buffer buf; /**< Buffer in which received datagrams
* are reassembled. */
};
/**
* List of fragment structures for reassembling multiple incoming packets
* concurrently.
*/
struct fragment_list {
int seq_id; /**< Highest fragmentation sequence ID of
* the packets currently being
* reassembled. */
int index; /**< Index of the packet being reassembled
* with the highest fragmentation
* sequence ID into the \c
* fragment_list.fragments array. */
/** Array of reassembly structures, each can contain one whole packet.
*
* The fragmentation sequence IDs of the packets being reassembled in
* this array are linearly increasing. \c
* fragment_list.fragments[fragment_list.index] has an ID of \c
* fragment_list.seq_id. This means that one of these \c fragment_list
* structures can at any one time contain at most packets with the
* fragmentation sequence IDs in the range \c fragment_list.seq_id \c -
* \c N_FRAG_BUF \c + \c 1 to \c fragment_list.seq_id, inclusive.
*/
struct fragment fragments[N_FRAG_BUF];
};
/**
* Fragmentation and reassembly state for one VPN tunnel instance.
*
* This structure contains all the state necessary for sending and
* receiving fragmented data channel packets associated with one VPN
* tunnel.
*
* The fragmented packet currently being sent to a remote OpenVPN peer is
* stored in \c fragment_master.outgoing. It is copied into that buffer
* by the \c fragment_outgoing() function and the remaining parts to be
* sent can be retrieved by successive calls to \c
* fragment_ready_to_send().
*
* The received packets currently being reassembled are stored in the \c
* fragment_master.incoming array of \c fragment structures. The \c
* fragment_incoming() function adds newly received parts into this array
* and returns the whole packets once reassembly is complete.
*/
struct fragment_master {
struct event_timeout wakeup; /**< Timeout structure used by the main
* event loop to know when to do
* fragmentation housekeeping. */
bool received_os_mtu_hint; /**< Whether the operating system has
* explicitly recommended an MTU value. */
#define N_SEQ_ID 256
/**< One more than the maximum fragment
* sequence ID, above which the IDs wrap
* to zero. Should be a power of 2. */
int outgoing_seq_id; /**< Fragment sequence ID of the current
* fragmented packet waiting to be sent.
*
* All parts of a fragmented packet
* share the same sequence ID, so that
* the remote OpenVPN peer can determine
* which parts belong to which original
* packet. */
#define MAX_FRAG_PKT_SIZE 65536
/**< (Not used) Maximum packet size before
* fragmenting. */
int outgoing_frag_size; /**< Size in bytes of each part to be
* sent, except for the last part which
* may be smaller.
*
* This value is computed by the \c
* optimal_fragment_size() function. Its
* value is sent to the remote peer in
* the fragmentation header of the last
* part (i.e. with %fragment type \c
* FRAG_YES_LAST) using the \c
* FRAG_SIZE_MASK and \c FRAG_SIZE_SHIFT
* bits. */
int outgoing_frag_id; /**< The fragment ID of the next part to
* be sent. Must have a value between 0
* and \c MAX_FRAGS-1. */
struct buffer outgoing; /**< Buffer containing the remaining parts
* of the fragmented packet being sent. */
struct buffer outgoing_return;
/**< Buffer used by \c
* fragment_ready_to_send() to return a
* part to send. */
struct fragment_list incoming;
/**< List of structures for reassembling
* incoming packets. */
};
/**************************************************************************/
/** @name Fragment header
* @todo Add description of %fragment header format.
*//** @{ *//*************************************/
typedef uint32_t fragment_header_type;
/**< Fragmentation information is stored in
* a 32-bit packet header. */
#define hton_fragment_header_type(x) htonl(x)
/**< Convert a fragment_header_type from
* host to network order. */
#define ntoh_fragment_header_type(x) ntohl(x)
/**< Convert a \c fragment_header_type
* from network to host order. */
#define FRAG_TYPE_MASK 0x00000003
/**< Bit mask for %fragment type info. */
#define FRAG_TYPE_SHIFT 0 /**< Bit shift for %fragment type info. */
#define FRAG_WHOLE 0 /**< Fragment type indicating packet is
* whole. */
#define FRAG_YES_NOTLAST 1 /**< Fragment type indicating packet is
* part of a fragmented packet, but not
* the last part in the sequence. */
#define FRAG_YES_LAST 2 /**< Fragment type indicating packet is
* the last part in the sequence of
* parts. */
#define FRAG_TEST 3 /**< Fragment type not implemented yet.
* In the future might be used as a
* control packet for establishing MTU
* size. */
#define FRAG_SEQ_ID_MASK 0x000000ff
/**< Bit mask for %fragment sequence ID. */
#define FRAG_SEQ_ID_SHIFT 2 /**< Bit shift for %fragment sequence ID. */
#define FRAG_ID_MASK 0x0000001f
/**< Bit mask for %fragment ID. */
#define FRAG_ID_SHIFT 10
/**< Bit shift for %fragment ID. */
/*
* FRAG_SIZE 14 bits
*
* IF FRAG_YES_LAST (FRAG_SIZE):
* The max size of a %fragment. If a %fragment is not the last %fragment in the packet,
* then the %fragment size is guaranteed to be equal to the max %fragment size. Therefore,
* max_frag_size is only sent over the wire if FRAG_LAST is set. Otherwise it is assumed
* to be the actual %fragment size received.
*/
#define FRAG_SIZE_MASK 0x00003fff
/**< Bit mask for %fragment size. */
#define FRAG_SIZE_SHIFT 15
/**< Bit shift for %fragment size. */
#define FRAG_SIZE_ROUND_SHIFT 2 /**< Bit shift for %fragment size rounding. */
#define FRAG_SIZE_ROUND_MASK ((1 << FRAG_SIZE_ROUND_SHIFT) - 1)
/**< Bit mask for %fragment size rounding. */
/*
* FRAG_EXTRA 16 bits
*
* IF FRAG_WHOLE or FRAG_YES_NOTLAST, these 16 bits are available (not currently used)
*/
#define FRAG_EXTRA_MASK 0x0000ffff
/**< Bit mask for extra bits. */
#define FRAG_EXTRA_SHIFT 15
/**< Bit shift for extra bits. */
/** @} name Fragment header *//********************************************/
/**************************************************************************/
/** @name Functions for initialization and cleanup *//** @{ *//************/
/**
* Allocate and initialize a \c fragment_master structure.
*
* This function also modifies the \a frame packet geometry parameters to
* include space for the fragmentation header.
*
* @param frame - The packet geometry parameters for this VPN
* tunnel, modified by this function to include the
* fragmentation header.
*
* @return A pointer to the new \c fragment_master structure.
*/
struct fragment_master *fragment_init(struct frame *frame);
/**
* Allocate internal packet buffers for a \c fragment_master structure.
*
* @param f - The \c fragment_master structure for which to
* allocate the internal buffers.
* @param frame - The packet geometry parameters for this VPN
* tunnel, used to determine how much memory to
* allocate for each packet buffer.
*/
void fragment_frame_init(struct fragment_master *f, const struct frame *frame);
/**
* Free a \c fragment_master structure and its internal packet buffers.
*
* @param f - The \c fragment_master structure to free.
*/
void fragment_free(struct fragment_master *f);
/** @} name Functions for initialization and cleanup *//*******************/
/**************************************************************************/
/** @name Functions for processing packets received from a remote OpenVPN peer */
/** @{ */
/**
* Process an incoming packet, which may or may not be fragmented.
*
* This function inspects the fragmentation header of the incoming packet
* and processes the packet accordingly. Depending on the %fragment type
* bits (\c FRAG_TYPE_MASK and \c FRAG_TYPE_SHIFT) the packet is processed
* in the following ways:
* - \c FRAG_WHOLE: the packet is not fragmented, and this function does
* not modify its contents, except for removing the fragmentation
* header.
* - \c FRAG_YES_NOTLAST or \c FRAG_YES_LAST: the packet is part of a
* fragmented packet. This function copies the packet into an internal
* reassembly buffer. If the incoming part completes the packet being
* reassembled, the \a buf argument is modified to point to the fully
* reassembled packet. If, on the other hand, reassembly is not yet
* complete, then the the \a buf buffer is set to empty.
* - Any other value: error.
*
* If an error occurs during processing, an error message is logged and
* the length of \a buf is set to zero.
*
* @param f - The \c fragment_master structure for this VPN
* tunnel.
* @param buf - A pointer to the buffer structure containing the
* incoming packet. This pointer will have been
* modified on return either to point to a
* completely reassembled packet, or to have length
* set to zero if reassembly is not yet complete.
* @param frame - The packet geometry parameters for this VPN
* tunnel.
*
* @return Void.\n On return, the \a buf argument will point to a buffer.
* The buffer will have nonzero length if the incoming packet passed
* to this function was whole and unfragmented, or if it was the final
* part of a fragmented packet thereby completing reassembly. On the
* other hand, the buffer will have a length of zero if the incoming
* packet was part of a fragmented packet and reassembly is not yet
* complete. If an error occurs during processing, the buffer length
* is also set to zero.
*/
void fragment_incoming(struct fragment_master *f, struct buffer *buf,
const struct frame *frame);
/** @} name Functions for processing packets received from a VPN tunnel */
/**************************************************************************/
/** @name Functions for processing packets to be sent to a remote OpenVPN peer */
/** @{ */
/**
* Process an outgoing packet, which may or may not need to be fragmented.
*
* This function inspects the outgoing packet, determines whether it needs
* to be fragmented, and processes it accordingly.
*
* Depending on the size of the outgoing packet and the packet geometry
* parameters for the VPN tunnel, the packet will or will not be
* fragmented.
* @li Packet size is less than or equal to the maximum packet size for
* this VPN tunnel: fragmentation is not necessary. The \a buf
* argument points to a buffer containing the unmodified outgoing
* packet with a fragmentation header indicating the packet is whole
* (FRAG_WHOLE) prepended.
* @li Packet size is greater than the maximum packet size for this VPN
* tunnel: fragmentation is necessary. The original outgoing packet
* is copied into an internal buffer for fragmentation. The \a buf
* argument is modified to point to the first part of the fragmented
* packet. The remaining parts remain stored in the internal buffer,
* and can be retrieved using the \c fragment_ready_to_send()
* function.
*
* If an error occurs during processing, an error message is logged and
* the length of \a buf is set to zero.
*
* @param f - The \c fragment_master structure for this VPN
* tunnel.
* @param buf - A pointer to the buffer structure containing the
* outgoing packet. This pointer will be modified
* to point to a whole unfragmented packet or to the
* first part of a fragmented packet on return.
* @param frame - The packet geometry parameters for this VPN
* tunnel.
*
* @return Void.\n On return, the \a buf argument will point to a buffer.
* This buffer contains either the whole original outgoing packet if
* fragmentation was not necessary, or the first part of the
* fragmented outgoing packet if fragmentation was necessary. In both
* cases a fragmentation header will have been prepended to inform the
* remote peer how to handle the packet.
*/
void fragment_outgoing(struct fragment_master *f, struct buffer *buf,
const struct frame *frame);
/**
* Check whether outgoing fragments are ready to be send, and if so make
* one available.
*
* This function checks whether the internal buffer for fragmenting
* outgoing packets contains any unsent parts. If it does not, meaning
* there is nothing waiting to be sent, it returns false. Otherwise there
* are parts ready to be sent, and it returns true. In that case it also
* modifies the \a buf argument to point to a buffer containing the next
* part to be sent.
*
* @param f - The \a fragment_master structure for this VPN
* tunnel.
* @param buf - A pointer to a buffer structure which on return,
* if there are parts waiting to be sent, will point
* to the next part to be sent.
* @param frame - The packet geometry parameters for this VPN
* tunnel.
*
* @return
* @li True, if an outgoing packet has been fragmented and not all parts
* have been sent yet. In this case this function will modify the \a
* buf argument to point to a buffer containing the next part to be
* sent.
* @li False, if there are no outgoing fragmented parts waiting to be
* sent.
*/
bool fragment_ready_to_send(struct fragment_master *f, struct buffer *buf,
const struct frame *frame);
/**
* Check whether a \c fragment_master structure contains fragments ready
* to be sent.
*
* @param f - The \c fragment_master structure for this VPN
* tunnel.
*
* @return
* @li True, if there are one or more fragments ready to be sent.
* @li False, otherwise.
*/
static inline bool
fragment_outgoing_defined(struct fragment_master *f)
{
return f->outgoing.len > 0;
}
/** @} name Functions for processing packets going out through a VPN tunnel */
void fragment_wakeup(struct fragment_master *f, struct frame *frame);
/**************************************************************************/
/** @name Functions for regular housekeeping *//** @{ *//******************/
/**
* Perform housekeeping of a \c fragment_master structure.
*
* Housekeeping includes scanning incoming packet reassembly buffers for
* packets which have not yet been reassembled completely but are already
* older than their time-to-live.
*
* @param f - The \c fragment_master structure for this VPN
* tunnel.
* @param frame - The packet geometry parameters for this VPN
* tunnel.
*/
static inline void
fragment_housekeeping(struct fragment_master *f, struct frame *frame, struct timeval *tv)
{
if (event_timeout_trigger(&f->wakeup, tv, ETT_DEFAULT))
{
fragment_wakeup(f, frame);
}
}
/** @} name Functions for regular housekeeping *//*************************/
/** @} addtogroup fragmentation *//****************************************/
#endif /* ifdef ENABLE_FRAGMENT */
#endif /* ifndef FRAGMENT_H */