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*
* 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
*/
/*
* These routines are designed to catch replay attacks,
* where a man-in-the-middle captures packets and then
* attempts to replay them back later.
*/
#ifdef USE_CRYPTO
#ifndef PACKET_ID_H
#define PACKET_ID_H
#include "circ_list.h"
#include "buffer.h"
#include "error.h"
#include "otime.h"
/*
* Enables OpenVPN to be compiled in special packet_id test mode.
*/
/*#define PID_TEST*/
#if 1
/*
* These are the types that members of
* a struct packet_id_net are converted
* to for network transmission.
*/
typedef uint32_t packet_id_type;
typedef uint32_t net_time_t;
/*
* In TLS mode, when a packet ID gets to this level,
* start thinking about triggering a new
* SSL/TLS handshake.
*/
#define PACKET_ID_WRAP_TRIGGER 0xFF000000
/* convert a packet_id_type from host to network order */
#define htonpid(x) htonl(x)
/* convert a packet_id_type from network to host order */
#define ntohpid(x) ntohl(x)
/* convert a time_t in host order to a net_time_t in network order */
#define htontime(x) htonl((net_time_t)x)
/* convert a net_time_t in network order to a time_t in host order */
#define ntohtime(x) ((time_t)ntohl(x))
#else
/*
* DEBUGGING ONLY.
* Make packet_id_type and net_time_t small
* to test wraparound logic and corner cases.
*/
typedef uint8_t packet_id_type;
typedef uint16_t net_time_t;
#define PACKET_ID_WRAP_TRIGGER 0x80
#define htonpid(x) (x)
#define ntohpid(x) (x)
#define htontime(x) htons((net_time_t)x)
#define ntohtime(x) ((time_t)ntohs(x))
#endif
/*
* Printf formats for special types
*/
#define packet_id_format "%u"
typedef unsigned int packet_id_print_type;
/*
* Maximum allowed backtrack in
* sequence number due to packets arriving
* out of order.
*/
#define MIN_SEQ_BACKTRACK 0
#define MAX_SEQ_BACKTRACK 65536
#define DEFAULT_SEQ_BACKTRACK 64
/*
* Maximum allowed backtrack in
* seconds due to packets arriving
* out of order.
*/
#define MIN_TIME_BACKTRACK 0
#define MAX_TIME_BACKTRACK 600
#define DEFAULT_TIME_BACKTRACK 15
/*
* Do a reap pass through the sequence number
* array once every n seconds in order to
* expire sequence numbers which can no longer
* be accepted because they would violate
* TIME_BACKTRACK.
*/
#define SEQ_REAP_INTERVAL 5
CIRC_LIST (seq_list, time_t);
/*
* This is the data structure we keep on the receiving side,
* to check that no packet-id (i.e. sequence number + optional timestamp)
* is accepted more than once.
*/
struct packet_id_rec
{
time_t last_reap; /* last call of packet_id_reap */
time_t time; /* highest time stamp received */
packet_id_type id; /* highest sequence number received */
int seq_backtrack; /* set from --replay-window */
int time_backtrack; /* set from --replay-window */
bool initialized; /* true if packet_id_init was called */
struct seq_list *seq_list; /* packet-id "memory" */
};
/*
* file to facilitate cross-session persistence
* of time/id
*/
struct packet_id_persist
{
const char *filename;
int fd;
time_t time; /* time stamp */
packet_id_type id; /* sequence number */
time_t time_last_written;
packet_id_type id_last_written;
};
struct packet_id_persist_file_image
{
time_t time; /* time stamp */
packet_id_type id; /* sequence number */
};
/*
* Keep a record of our current packet-id state
* on the sending side.
*/
struct packet_id_send
{
packet_id_type id;
time_t time;
};
/*
* Communicate packet-id over the wire.
* A short packet-id is just a 32 bit
* sequence number. A long packet-id
* includes a timestamp as well.
*
* Long packet-ids are used as IVs for
* CFB/OFB ciphers.
*
* This data structure is always sent
* over the net in network byte order,
* by calling htonpid, ntohpid,
* htontime, and ntohtime on the
* data elements to change them
* to and from standard sizes.
*
* In addition, time is converted to
* a net_time_t before sending,
* since openvpn always
* uses a 32-bit time_t but some
* 64 bit platforms use a
* 64 bit time_t.
*/
struct packet_id_net
{
packet_id_type id;
time_t time; /* converted to net_time_t before transmission */
};
struct packet_id
{
struct packet_id_send send;
struct packet_id_rec rec;
};
void packet_id_init (struct packet_id *p, int seq_backtrack, int time_backtrack);
void packet_id_free (struct packet_id *p);
/* should we accept an incoming packet id ? */
bool packet_id_test (const struct packet_id_rec *p,
const struct packet_id_net *pin);
/* change our current state to reflect an accepted packet id */
void packet_id_add (struct packet_id_rec *p,
const struct packet_id_net *pin);
/* expire TIME_BACKTRACK sequence numbers */
void packet_id_reap (struct packet_id_rec *p);
/*
* packet ID persistence
*/
/* initialize the packet_id_persist structure in a disabled state */
void packet_id_persist_init (struct packet_id_persist *p);
/* close the file descriptor if it is open, and switch to disabled state */
void packet_id_persist_close (struct packet_id_persist *p);
/* load persisted rec packet_id (time and id) only once from file, and set state to enabled */
void packet_id_persist_load (struct packet_id_persist *p, const char *filename);
/* save persisted rec packet_id (time and id) to file (only if enabled state) */
void packet_id_persist_save (struct packet_id_persist *p);
/* transfer packet_id_persist -> packet_id */
void packet_id_persist_load_obj (const struct packet_id_persist *p, struct packet_id* pid);
/* return an ascii string representing a packet_id_persist object */
const char *packet_id_persist_print (const struct packet_id_persist *p, struct gc_arena *gc);
/*
* Read/write a packet ID to/from the buffer. Short form is sequence number
* only. Long form is sequence number and timestamp.
*/
bool packet_id_read (struct packet_id_net *pin, struct buffer *buf, bool long_form);
bool packet_id_write (const struct packet_id_net *pin, struct buffer *buf, bool long_form, bool prepend);
/*
* Inline functions.
*/
/* are we in enabled state? */
static inline bool
packet_id_persist_enabled (const struct packet_id_persist *p)
{
return p->fd >= 0;
}
/* transfer packet_id -> packet_id_persist */
static inline void
packet_id_persist_save_obj (struct packet_id_persist *p, const struct packet_id* pid)
{
if (packet_id_persist_enabled (p) && pid->rec.time)
{
p->time = pid->rec.time;
p->id = pid->rec.id;
}
}
const char* packet_id_net_print(const struct packet_id_net *pin, bool print_timestamp, struct gc_arena *gc);
#ifdef PID_TEST
void packet_id_interactive_test();
#endif
static inline int
packet_id_size (bool long_form)
{
return sizeof (packet_id_type) + (long_form ? sizeof (net_time_t) : 0);
}
static inline bool
packet_id_close_to_wrapping (const struct packet_id_send *p)
{
return p->id >= PACKET_ID_WRAP_TRIGGER;
}
/*
* Allocate an outgoing packet id.
* Sequence number ranges from 1 to 2^32-1.
* In long_form, a time_t is added as well.
*/
static inline void
packet_id_alloc_outgoing (struct packet_id_send *p, struct packet_id_net *pin, bool long_form)
{
if (!p->time)
p->time = now;
pin->id = ++p->id;
if (!pin->id)
{
ASSERT (long_form);
p->time = now;
pin->id = p->id = 1;
}
pin->time = p->time;
}
static inline bool
check_timestamp_delta (time_t remote, unsigned int max_delta)
{
unsigned int abs;
const time_t local_now = now;
if (local_now >= remote)
abs = local_now - remote;
else
abs = remote - local_now;
return abs <= max_delta;
}
static inline void
packet_id_reap_test (struct packet_id_rec *p)
{
if (p->last_reap + SEQ_REAP_INTERVAL <= now)
packet_id_reap (p);
}
#endif /* PACKET_ID_H */
#endif /* USE_CRYPTO */ |