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-rw-r--r--src/openvpn/packet_id.c492
1 files changed, 492 insertions, 0 deletions
diff --git a/src/openvpn/packet_id.c b/src/openvpn/packet_id.c
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+/*
+ * 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.
+ */
+
+#ifdef WIN32
+#include "config-win32.h"
+#else
+#include "config.h"
+#endif
+
+#ifdef USE_CRYPTO
+
+#include "syshead.h"
+
+#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 1 and must increment linearly without gaps.
+ *
+ * This mode is used with TCP.
+ */
+ if (pin->time == p->time)
+ return 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 */
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