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Diffstat (limited to 'packet_id.h')
| -rw-r--r-- | packet_id.h | 335 |
1 files changed, 335 insertions, 0 deletions
diff --git a/packet_id.h b/packet_id.h new file mode 100644 index 0000000..12c1df3 --- /dev/null +++ b/packet_id.h @@ -0,0 +1,335 @@ +/* + * 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 + */ + +/* + * 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 */ |