/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single TCP/UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2002-2010 OpenVPN Technologies, 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 (see the file COPYING included with this
* distribution); if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef MTU_H
#define MTU_H
#include "buffer.h"
/*
*
* Packet maninipulation routes such as encrypt, decrypt, compress, decompress
* are passed a frame buffer that looks like this:
*
* [extra_frame bytes] [mtu bytes] [extra_frame_bytes] [compression overflow bytes]
* ^
* Pointer passed to function points here so that routine
* can make use of extra_frame bytes before pointer
* to prepend headers, etc.
*
* extra_frame bytes is large enough for all encryption related overhead.
*
* mtu bytes will be the MTU size set in the ifconfig statement that configures
* the TUN or TAP device such as:
*
* ifconfig $1 10.1.0.2 pointopoint 10.1.0.1 mtu 1450
*
* Compression overflow bytes is the worst-case size expansion that would be
* expected if we tried to compress mtu + extra_frame bytes of uncompressible data.
*/
/*
* Standard ethernet MTU
*/
#define ETHERNET_MTU 1500
/*
* It is a fatal error if mtu is less than
* this value for tun device.
*/
#define TUN_MTU_MIN 100
/*
* Default MTU of network over which tunnel data will pass by TCP/UDP.
*/
#define LINK_MTU_DEFAULT 1500
/*
* Default MTU of tunnel device.
*/
#define TUN_MTU_DEFAULT 1500
/*
* MTU Defaults for TAP devices
*/
#define TAP_MTU_EXTRA_DEFAULT 32
/*
* Default MSSFIX value, used for reducing TCP MTU size
*/
#define MSSFIX_DEFAULT 1450
/*
* Alignment of payload data such as IP packet or
* ethernet frame.
*/
#define PAYLOAD_ALIGN 4
struct frame {
/*
* Maximum datagram size to be sent over the tunnel TCP/UDP channel.
*/
int link_mtu;
int link_mtu_dynamic;
/*
* How many extra bytes might each subsystem (crypto, TLS, or, compression)
* add to frame in worst case?
*
* mtu + extra_frame = MTU of TCP/UDP transport
*/
int extra_frame;
/*
* Worst case size added to internal buffer due to functions
* such as compression which can potentially expand the size of uncompressible
* data.
*/
int extra_buffer;
/*
* Max number of bytes in excess of tun mtu size that we might read
* or write from TUN/TAP device.
*/
int extra_tun;
/*
* Max number of bytes in excess of link mtu size that we might read
* or write from UDP/TCP link.
*/
int extra_link;
/*
* Alignment control
*/
# define FRAME_HEADROOM_MARKER_DECRYPT (1<<0)
# define FRAME_HEADROOM_MARKER_FRAGMENT (1<<1)
# define FRAME_HEADROOM_MARKER_READ_LINK (1<<2)
# define FRAME_HEADROOM_MARKER_READ_STREAM (1<<3)
unsigned int align_flags;
int align_adjust;
};
/* Routines which read struct frame should use the macros below */
/*
* Overhead added to packet payload due to encapsulation
*/
#define EXTRA_FRAME(f) ((f)->extra_frame)
/*
* Delta between tun payload size and final TCP/UDP datagram size
* (not including extra_link additions)
*/
#define TUN_LINK_DELTA(f) ((f)->extra_frame + (f)->extra_tun)
/*
* This is the size to "ifconfig" the tun or tap device.
*/
#define TUN_MTU_SIZE(f) ((f)->link_mtu - TUN_LINK_DELTA(f))
#define TUN_MTU_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic - TUN_LINK_DELTA(f))
/*
* This is the maximum packet size that we need to be able to
* read from or write to a tun or tap device. For example,
* a tap device ifconfiged to an MTU of 1200 might actually want
* to return a packet size of 1214 on a read().
*/
#define PAYLOAD_SIZE(f) ((f)->link_mtu - (f)->extra_frame)
#define PAYLOAD_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic - (f)->extra_frame)
/*
* Max size of a payload packet after encryption, compression, etc.
* overhead is added.
*/
#define EXPANDED_SIZE(f) ((f)->link_mtu)
#define EXPANDED_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic)
#define EXPANDED_SIZE_MIN(f) (TUN_MTU_MIN + TUN_LINK_DELTA(f))
/*
* These values are used as maximum size constraints
* on read() or write() from TUN/TAP device or TCP/UDP port.
*/
#define MAX_RW_SIZE_TUN(f) (PAYLOAD_SIZE(f))
#define MAX_RW_SIZE_LINK(f) (EXPANDED_SIZE(f) + (f)->extra_link)
/*
* Control buffer headroom allocations to allow for efficient prepending.
*/
#define FRAME_HEADROOM_BASE(f) (TUN_LINK_DELTA(f) + (f)->extra_buffer + (f)->extra_link)
#define FRAME_HEADROOM(f) frame_headroom(f, 0)
#define FRAME_HEADROOM_ADJ(f, fm) frame_headroom(f, fm)
/*
* Max size of a buffer used to build a packet for output to
* the TCP/UDP port.
*/
#define BUF_SIZE(f) (TUN_MTU_SIZE(f) + FRAME_HEADROOM_BASE(f) * 2)
/*
* Function prototypes.
*/
void frame_finalize (struct frame *frame,
bool link_mtu_defined,
int link_mtu,
bool tun_mtu_defined,
int tun_mtu);
void frame_subtract_extra (struct frame *frame, const struct frame *src);
void frame_print (const struct frame *frame,
int level,
const char *prefix);
void set_mtu_discover_type (int sd, int mtu_type);
int translate_mtu_discover_type_name (const char *name);
/*
* frame_set_mtu_dynamic and flags
*/
#define SET_MTU_TUN (1<<0) /* use tun/tap rather than link sizing */
#define SET_MTU_UPPER_BOUND (1<<1) /* only decrease dynamic MTU */
void frame_set_mtu_dynamic (struct frame *frame, int mtu, unsigned int flags);
/*
* allocate a buffer for socket or tun layer
*/
void alloc_buf_sock_tun (struct buffer *buf,
const struct frame *frame,
const bool tuntap_buffer,
const unsigned int align_mask);
/*
* EXTENDED_SOCKET_ERROR_CAPABILITY functions -- print extra error info
* on socket errors, such as PMTU size. As of 2003.05.11, only works
* on Linux 2.4+.
*/
#if EXTENDED_SOCKET_ERROR_CAPABILITY
void set_sock_extended_error_passing (int sd);
const char *format_extended_socket_error (int fd, int *mtu, struct gc_arena *gc);
#endif
/*
* Calculate a starting offset into a buffer object, dealing with
* headroom and alignment issues.
*/
static inline int
frame_headroom (const struct frame *f, const unsigned int flag_mask)
{
const int offset = FRAME_HEADROOM_BASE (f);
const int adjust = (flag_mask & f->align_flags) ? f->align_adjust : 0;
const int delta = ((PAYLOAD_ALIGN << 24) - (offset + adjust)) & (PAYLOAD_ALIGN - 1);
return offset + delta;
}
/*
* frame member adjustment functions
*/
static inline void
frame_add_to_extra_frame (struct frame *frame, const int increment)
{
frame->extra_frame += increment;
}
static inline void
frame_add_to_extra_tun (struct frame *frame, const int increment)
{
frame->extra_tun += increment;
}
static inline void
frame_add_to_extra_link (struct frame *frame, const int increment)
{
frame->extra_link += increment;
}
static inline void
frame_add_to_extra_buffer (struct frame *frame, const int increment)
{
frame->extra_buffer += increment;
}
static inline void
frame_add_to_align_adjust (struct frame *frame, const int increment)
{
frame->align_adjust += increment;
}
static inline void
frame_align_to_extra_frame (struct frame *frame)
{
frame->align_adjust = frame->extra_frame + frame->extra_link;
}
static inline void
frame_or_align_flags (struct frame *frame, const unsigned int flag_mask)
{
frame->align_flags |= flag_mask;
}
static inline bool
frame_defined (const struct frame *frame)
{
return frame->link_mtu > 0;
}
#endif
