/*
* 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) 2002-2005 OpenVPN Solutions LLC <info@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
*/
/*
* These routines are designed to catch replay attacks,
* where a man-in-the-middle captures packets and then
* attempts to replay them back later.
*
* We use the "sliding-window" algorithm, similar
* to IPSec.
*/
#include "syshead.h"
#ifdef USE_CRYPTO
#include "packet_id.h"
#include "misc.h"
#include "integer.h"
#include "memdbg.h"
/*
* Special time_t value that indicates that
* sequence number has expired.
*/
#define SEQ_UNSEEN ((time_t)0)
#define SEQ_EXPIRED ((time_t)1)
void
packet_id_init (struct packet_id *p, int seq_backtrack, int time_backtrack)
{
dmsg (D_PID_DEBUG_LOW, "PID packet_id_init seq_backtrack=%d time_backtrack=%d",
seq_backtrack,
time_backtrack);
ASSERT (p);
CLEAR (*p);
if (seq_backtrack)
{
ASSERT (MIN_SEQ_BACKTRACK <= seq_backtrack && seq_backtrack <= MAX_SEQ_BACKTRACK);
ASSERT (MIN_TIME_BACKTRACK <= time_backtrack && time_backtrack <= MAX_TIME_BACKTRACK);
CIRC_LIST_ALLOC (p->rec.seq_list, struct seq_list, seq_backtrack);
p->rec.seq_backtrack = seq_backtrack;
p->rec.time_backtrack = time_backtrack;
}
p->rec.initialized = true;
}
void
packet_id_free (struct packet_id *p)
{
if (p)
{
dmsg (D_PID_DEBUG_LOW, "PID packet_id_free");
if (p->rec.seq_list)
free (p->rec.seq_list);
CLEAR (*p);
}
}
void
packet_id_add (struct packet_id_rec *p, const struct packet_id_net *pin)
{
const time_t local_now = now;
if (p->seq_list)
{
packet_id_type diff;
/*
* If time value increases, start a new
* sequence number sequence.
*/
if (!CIRC_LIST_SIZE (p->seq_list)
|| pin->time > p->time
|| (pin->id >= (packet_id_type)p->seq_backtrack
&& pin->id - (packet_id_type)p->seq_backtrack > p->id))
{
p->time = pin->time;
p->id = 0;
if (pin->id > (packet_id_type)p->seq_backtrack)
p->id = pin->id - (packet_id_type)p->seq_backtrack;
CIRC_LIST_RESET (p->seq_list);
}
while (p->id < pin->id)
{
CIRC_LIST_PUSH (p->seq_list, SEQ_UNSEEN);
++p->id;
}
diff = p->id - pin->id;
if (diff < (packet_id_type) CIRC_LIST_SIZE (p->seq_list)
&& local_now > SEQ_EXPIRED)
CIRC_LIST_ITEM (p->seq_list, diff) = local_now;
}
else
{
p->time = pin->time;
p->id = pin->id;
}
}
/*
* Expire sequence numbers which can no longer
* be accepted because they would violate
* time_backtrack.
*/
void
packet_id_reap (struct packet_id_rec *p)
{
const time_t local_now = now;
if (p->time_backtrack)
{
int i;
bool expire = false;
for (i = 0; i < CIRC_LIST_SIZE (p->seq_list); ++i)
{
const time_t t = CIRC_LIST_ITEM (p->seq_list, i);
if (t == SEQ_EXPIRED)
break;
if (!expire && t && t + p->time_backtrack < local_now)
expire = true;
if (expire)
CIRC_LIST_ITEM (p->seq_list, i) = SEQ_EXPIRED;
}
}
p->last_reap = local_now;
}
/*
* Return true if packet id is ok, or false if
* it is a replay.
*/
bool
packet_id_test (const struct packet_id_rec *p,
const struct packet_id_net *pin)
{
static int max_backtrack_stat;
packet_id_type diff;
dmsg (D_PID_DEBUG,
"PID TEST " time_format ":" packet_id_format " " time_format ":" packet_id_format "",
(time_type)p->time, (packet_id_print_type)p->id, (time_type)pin->time,
(packet_id_print_type)pin->id);
ASSERT (p->initialized);
if (!pin->id)
return false;
if (p->seq_backtrack)
{
/*
* In backtrack mode, we allow packet reordering subject
* to the seq_backtrack and time_backtrack constraints.
*
* This mode is used with UDP.
*/
if (pin->time == p->time)
{
/* is packet-id greater than any one we've seen yet? */
if (pin->id > p->id)
return true;
/* check packet-id sliding window for original/replay status */
diff = p->id - pin->id;
/* keep track of maximum backtrack seen for debugging purposes */
if ((int)diff > max_backtrack_stat)
{
max_backtrack_stat = (int)diff;
msg (D_BACKTRACK, "Replay-window backtrack occurred [%d]", max_backtrack_stat);
}
if (diff >= (packet_id_type) CIRC_LIST_SIZE (p->seq_list))
return false;
return CIRC_LIST_ITEM (p->seq_list, diff) == 0;
}
else if (pin->time < p->time) /* if time goes back, reject */
return false;
else /* time moved forward */
return true;
}
else
{
/*
* In non-backtrack mode, all sequence number series must
* begin at some number n > 0 and must increment linearly without gaps.
*
* This mode is used with TCP.
*/
if (pin->time == p->time)
return !p->id || pin->id == p->id + 1;
else if (pin->time < p->time) /* if time goes back, reject */
return false;
else /* time moved forward */
return pin->id == 1;
}
}
/*
* 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)
{
packet_id_type net_id;
net_time_t net_time;
pin->id = 0;
pin->time = 0;
if (!buf_read (buf, &net_id, sizeof (net_id)))
return false;
pin->id = ntohpid (net_id);
if (long_form)
{
if (!buf_read (buf, &net_time, sizeof (net_time)))
return false;
pin->time = ntohtime (net_time);
}
return true;
}
bool
packet_id_write (const struct packet_id_net *pin, struct buffer *buf, bool long_form, bool prepend)
{
packet_id_type net_id = htonpid (pin->id);
net_time_t net_time = htontime (pin->time);
if (prepend)
{
if (long_form)
{
if (!buf_write_prepend (buf, &net_time, sizeof (net_time)))
return false;
}
if (!buf_write_prepend (buf, &net_id, sizeof (net_id)))
return false;
}
else
{
if (!buf_write (buf, &net_id, sizeof (net_id)))
return false;
if (long_form)
{
if (!buf_write (buf, &net_time, sizeof (net_time)))
return false;
}
}
return true;
}
const char *
packet_id_net_print (const struct packet_id_net *pin, bool print_timestamp, struct gc_arena *gc)
{
struct buffer out = alloc_buf_gc (256, gc);
buf_printf (&out, "[ #" packet_id_format, (packet_id_print_type)pin->id);
if (print_timestamp && pin->time)
buf_printf (&out, " / time = (" packet_id_format ") %s",
(packet_id_print_type)pin->time,
time_string (pin->time, 0, false, gc));
buf_printf (&out, " ]");
return BSTR (&out);
}
/* initialize the packet_id_persist structure in a disabled state */
void
packet_id_persist_init (struct packet_id_persist *p)
{
p->filename = NULL;
p->fd = -1;
p->time = p->time_last_written = 0;
p->id = p->id_last_written = 0;
}
/* close the file descriptor if it is open, and switch to disabled state */
void
packet_id_persist_close (struct packet_id_persist *p)
{
if (packet_id_persist_enabled (p))
{
if (close (p->fd))
msg (D_PID_PERSIST | M_ERRNO, "Close error on --replay-persist file %s", p->filename);
packet_id_persist_init (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)
{
struct gc_arena gc = gc_new ();
if (!packet_id_persist_enabled (p))
{
/* open packet-id persist file for both read and write */
p->fd = open (filename,
O_CREAT | O_RDWR | O_BINARY,
S_IRUSR | S_IWUSR);
if (p->fd == -1)
{
msg (D_PID_PERSIST | M_ERRNO,
"Cannot open --replay-persist file %s for read/write",
filename);
}
else
{
struct packet_id_persist_file_image image;
ssize_t n;
#if defined(HAVE_FLOCK) && defined(LOCK_EX) && defined(LOCK_NB)
if (flock (p->fd, LOCK_EX | LOCK_NB))
msg (M_ERR, "Cannot obtain exclusive lock on --replay-persist file %s", filename);
#endif
p->filename = filename;
n = read (p->fd, &image, sizeof(image));
if (n == sizeof(image))
{
p->time = p->time_last_written = image.time;
p->id = p->id_last_written = image.id;
dmsg (D_PID_PERSIST_DEBUG, "PID Persist Read from %s: %s",
p->filename, packet_id_persist_print (p, &gc));
}
else if (n == -1)
{
msg (D_PID_PERSIST | M_ERRNO,
"Read error on --replay-persist file %s",
p->filename);
}
}
}
gc_free (&gc);
}
/* save persisted rec packet_id (time and id) to file (only if enabled state) */
void
packet_id_persist_save (struct packet_id_persist *p)
{
if (packet_id_persist_enabled (p) && p->time && (p->time != p->time_last_written ||
p->id != p->id_last_written))
{
struct packet_id_persist_file_image image;
ssize_t n;
off_t seek_ret;
struct gc_arena gc = gc_new ();
image.time = p->time;
image.id = p->id;
seek_ret = lseek(p->fd, (off_t)0, SEEK_SET);
if (seek_ret == (off_t)0)
{
n = write(p->fd, &image, sizeof(image));
if (n == sizeof(image))
{
p->time_last_written = p->time;
p->id_last_written = p->id;
dmsg (D_PID_PERSIST_DEBUG, "PID Persist Write to %s: %s",
p->filename, packet_id_persist_print (p, &gc));
}
else
{
msg (D_PID_PERSIST | M_ERRNO,
"Cannot write to --replay-persist file %s",
p->filename);
}
}
else
{
msg (D_PID_PERSIST | M_ERRNO,
"Cannot seek to beginning of --replay-persist file %s",
p->filename);
}
gc_free (&gc);
}
}
/* transfer packet_id_persist -> packet_id */
void
packet_id_persist_load_obj (const struct packet_id_persist *p, struct packet_id *pid)
{
if (p && pid && packet_id_persist_enabled (p) && p->time)
{
pid->rec.time = p->time;
pid->rec.id = p->id;
}
}
const char *
packet_id_persist_print (const struct packet_id_persist *p, struct gc_arena *gc)
{
struct buffer out = alloc_buf_gc (256, gc);
buf_printf (&out, "[");
if (packet_id_persist_enabled (p))
{
buf_printf (&out, " #" packet_id_format, (packet_id_print_type)p->id);
if (p->time)
buf_printf (&out, " / time = (" packet_id_format ") %s",
(packet_id_print_type)p->time,
time_string (p->time, 0, false, gc));
}
buf_printf (&out, " ]");
return (char *)out.data;
}
#ifdef PID_TEST
void
packet_id_interactive_test ()
{
struct packet_id pid;
struct packet_id_net pin;
bool long_form;
bool count = 0;
bool test;
const int seq_backtrack = 10;
const int time_backtrack = 10;
packet_id_init (&pid, seq_backtrack, time_backtrack);
while (true) {
char buf[80];
if (!fgets(buf, sizeof(buf), stdin))
break;
update_time ();
if (sscanf (buf, "%lu,%u", &pin.time, &pin.id) == 2)
{
packet_id_reap_test (&pid.rec);
test = packet_id_test (&pid.rec, &pin);
printf ("packet_id_test (" time_format ", " packet_id_format ") returned %d\n",
(time_type)pin.time,
(packet_id_print_type)pin.id,
test);
if (test)
packet_id_add (&pid.rec, &pin);
}
else
{
long_form = (count < 20);
packet_id_alloc_outgoing (&pid.send, &pin, long_form);
printf ("(" time_format "(" packet_id_format "), %d)\n",
(time_type)pin.time,
(packet_id_print_type)pin.id,
long_form);
if (pid.send.id == 10)
pid.send.id = 0xFFFFFFF8;
++count;
}
}
packet_id_free (&pid);
}
#endif
#endif /* USE_CRYPTO */
