[PATCH 6/6] site: New PROD message
Ian Jackson
ijackson at chiark.greenend.org.uk
Wed Jul 17 14:07:53 BST 2013
We introduce a new message PROD which requests that the peer initiate
a key exchange with us, if it doesn't already have a key.
This helps significantly reduce a possible "dead period" when one end
of a connection is restarted during key exchange. The dead period is
now limited to the time taken for the interrupted key exchange to time
out.
Signed-off-by: Ian Jackson <ijackson at chiark.greenend.org.uk>
---
NOTES | 34 +++++++++++++++++++++++
magic.h | 1 +
site.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++----------
udp.c | 1 +
4 files changed, 113 insertions(+), 15 deletions(-)
diff --git a/NOTES b/NOTES
index 477104f..a4e6b21 100644
--- a/NOTES
+++ b/NOTES
@@ -276,3 +276,37 @@ vaguely recent version of secnet. (In fact, there is no evidence in
the git history of it ever being sent.)
This message number is reserved.
+
+11) *,*,PROD,A,B
+
+Sent in response to a NAK from B to A. Requests that B initiates a
+key exchange with A, if B is willing and lacks a transport key for A.
+(If B doesn't have A's address configured, implicitly supplies A's
+public address.)
+
+This is necessary because if one end of a link (B) is restarted while
+a key exchange is in progress, the following bad state can persist:
+the non-restarted end (A) thinks that the key is still valid and keeps
+sending packets, but B either doesn't realise that a key exchange with
+A is necessary or (if A is a mobile site) doesn't know A's public IP
+address.
+
+Normally in these circumstances B would send NAKs to A, causing A to
+initiate a key exchange. However if A and B were already in the
+middle of a key exchange then A will not want to try another one until
+the first one has timed out ("setup-time" x "setup-retries") and then
+the key exchange retry timeout ("wait-time") has elapsed.
+
+However if B's setup has timed out, B would be willing to participate
+in a key exchange initiated by A, if A could be induced to do so.
+This is the purpose of the PROD packet.
+
+We send no more PRODs than we would want to send data packets, to
+avoid a traffic amplification attack. We also send them only in state
+WAIT, as in other states we wouldn't respond favourably. And we only
+honour them if we don't already have a key.
+
+With PROD, the period of broken communication due to a key exchange
+interrupted by a restart is limited to the key exchange total
+retransmission timeout, rather than also including the key exchange
+retry timeout.
diff --git a/magic.h b/magic.h
index c2503a0c..7d2f427 100644
--- a/magic.h
+++ b/magic.h
@@ -14,5 +14,6 @@
#define LABEL_MSG7 0x07070707
#define LABEL_MSG8 0x08080808
#define LABEL_MSG9 0x09090909
+#define LABEL_PROD 0x0a0a0a0a
#endif /* magic_h */
diff --git a/site.c b/site.c
index aecd64d..8de482b 100644
--- a/site.c
+++ b/site.c
@@ -204,7 +204,8 @@ static void transport_peers_copy(struct site *st, transport_peers *dst,
static void transport_setup_msgok(struct site *st, const struct comm_addr *a);
static void transport_data_msgok(struct site *st, const struct comm_addr *a);
static bool_t transport_compute_setupinit_peers(struct site *st,
- const struct comm_addr *configured_addr /* 0 if none or not found */);
+ const struct comm_addr *configured_addr /* 0 if none or not found */,
+ const struct comm_addr *prod_hint_addr /* 0 if none */);
static void transport_record_peer(struct site *st, transport_peers *peers,
const struct comm_addr *addr, const char *m);
@@ -263,6 +264,7 @@ struct site {
/* runtime information */
uint32_t state;
uint64_t now; /* Most recently seen time */
+ bool_t allow_send_prod;
/* The currently established session */
struct data_key current;
@@ -327,7 +329,8 @@ static void delete_one_key(struct site *st, struct data_key *key,
const char *reason /* may be 0 meaning don't log*/,
const char *which /* ignored if !reasonn */,
uint32_t loglevel /* ignored if !reasonn */);
-static bool_t initiate_key_setup(struct site *st, cstring_t reason);
+static bool_t initiate_key_setup(struct site *st, cstring_t reason,
+ const struct comm_addr *prod_hint);
static void enter_state_run(struct site *st);
static bool_t enter_state_resolve(struct site *st);
static bool_t enter_new_state(struct site *st,uint32_t next);
@@ -418,6 +421,10 @@ static bool_t unpick_msg(struct site *st, uint32_t type,
m->loclen=buf_unprepend_uint16(msg);
CHECK_AVAIL(msg,m->loclen);
m->local=buf_unprepend(msg,m->loclen);
+ if (type==LABEL_PROD) {
+ CHECK_EMPTY(msg);
+ return True;
+ }
CHECK_AVAIL(msg,NONCELEN);
m->nR=buf_unprepend(msg,NONCELEN);
if (type==LABEL_MSG1) {
@@ -794,7 +801,7 @@ static bool_t decrypt_msg0(struct site *st, struct buffer_if *msg0)
slog(st,LOG_SEC,"transform: %s (aux: %s, new: %s)",
transform_err,auxkey_err,newkey_err);
- initiate_key_setup(st,"incoming message would not decrypt");
+ initiate_key_setup(st,"incoming message would not decrypt",0);
return False;
}
@@ -819,7 +826,7 @@ static bool_t process_msg0(struct site *st, struct buffer_if *msg0,
transport_data_msgok(st,src);
/* See whether we should start negotiating a new key */
if (st->now > st->renegotiate_key_time)
- initiate_key_setup(st,"incoming packet in renegotiation window");
+ initiate_key_setup(st,"incoming packet in renegotiation window",0);
return True;
default:
slog(st,LOG_SEC,"incoming encrypted message of type %08x "
@@ -900,7 +907,7 @@ static void site_resolve_callback(void *sst, struct in_addr *address)
slog(st,LOG_ERROR,"resolution of %s failed",st->address);
ca_use=0;
}
- if (transport_compute_setupinit_peers(st,ca_use)) {
+ if (transport_compute_setupinit_peers(st,ca_use,0)) {
enter_new_state(st,SITE_SENTMSG1);
} else {
/* Can't figure out who to try to to talk to */
@@ -909,14 +916,15 @@ static void site_resolve_callback(void *sst, struct in_addr *address)
}
}
-static bool_t initiate_key_setup(struct site *st, cstring_t reason)
+static bool_t initiate_key_setup(struct site *st, cstring_t reason,
+ const struct comm_addr *prod_hint)
{
if (st->state!=SITE_RUN) return False;
slog(st,LOG_SETUP_INIT,"initiating key exchange (%s)",reason);
if (st->address) {
slog(st,LOG_SETUP_INIT,"resolving peer address");
return enter_state_resolve(st);
- } else if (transport_compute_setupinit_peers(st,0)) {
+ } else if (transport_compute_setupinit_peers(st,0,prod_hint)) {
return enter_new_state(st,SITE_SENTMSG1);
}
slog(st,LOG_SETUP_INIT,"key exchange failed: no address for peer");
@@ -1126,6 +1134,30 @@ static void enter_state_wait(struct site *st)
/* XXX Erase keys etc. */
}
+static void generate_prod(struct site *st, struct buffer_if *buf)
+{
+ buffer_init(buf,0);
+ buf_append_uint32(buf,0);
+ buf_append_uint32(buf,0);
+ buf_append_uint32(buf,LABEL_PROD);
+ buf_append_string(buf,st->localname);
+ buf_append_string(buf,st->remotename);
+}
+
+static void generate_send_prod(struct site *st,
+ const struct comm_addr *source)
+{
+ if (!st->allow_send_prod) return; /* too soon */
+ if (!(st->state==SITE_RUN || st->state==SITE_RESOLVE ||
+ st->state==SITE_WAIT)) return; /* we'd ignore peer's MSG1 */
+
+ slog(st,LOG_SETUP_INIT,"prodding peer for key exchange)");
+ st->allow_send_prod=0;
+ generate_prod(st,&st->scratch);
+ dump_packet(st,&st->scratch,source,False);
+ source->comm->sendmsg(source->comm->st, &st->scratch, source);
+}
+
static inline void site_settimeout(uint64_t timeout, int *timeout_io)
{
if (timeout) {
@@ -1198,6 +1230,8 @@ static void site_outgoing(void *sst, struct buffer_if *buf)
return;
}
+ st->allow_send_prod=1;
+
/* In all other states we consider delivering the packet if we have
a valid key and a valid address to send it to. */
if (current_valid(st) && transport_peers_valid(&st->peers)) {
@@ -1217,7 +1251,7 @@ static void site_outgoing(void *sst, struct buffer_if *buf)
slog(st,LOG_DROP,"discarding outgoing packet of size %d",buf->size);
BUF_FREE(buf);
- initiate_key_setup(st,"outgoing packet");
+ initiate_key_setup(st,"outgoing packet",0);
}
static bool_t named_for_us(struct site *st, struct buffer_if *buf,
@@ -1233,7 +1267,10 @@ static bool_t named_for_us(struct site *st, struct buffer_if *buf,
}
/* This function is called by the communication device to deliver
- packets from our peers. */
+ packets from our peers.
+ It should return True if the packet is recognised as being for
+ this current site instance (and should therefore not be processed
+ by other sites), even if the packet was otherwise ignored. */
static bool_t site_incoming(void *sst, struct buffer_if *buf,
const struct comm_addr *source)
{
@@ -1288,6 +1325,20 @@ static bool_t site_incoming(void *sst, struct buffer_if *buf,
BUF_FREE(buf);
return True;
}
+ if (msgtype==LABEL_PROD && named_for_us(st,buf,0)) {
+ struct msg m;
+ dump_packet(st,buf,source,True);
+ if (!unpick_msg(st,LABEL_PROD,buf,&m)) {
+ slog(st,LOG_ERROR,"failed to unpick incoming PROD");
+ } else if (st->state!=SITE_RUN) {
+ slog(st,LOG_DROP,"ignoring PROD when not in state RUN");
+ } else if (current_valid(st)) {
+ slog(st,LOG_DROP,"ignoring PROD when we think we have a key");
+ } else {
+ initiate_key_setup(st,"peer sent PROD packet",source);
+ }
+ return True;
+ }
if (dest==st->index) {
/* Explicitly addressed to us */
if (msgtype!=LABEL_MSG0) dump_packet(st,buf,source,True);
@@ -1296,7 +1347,9 @@ static bool_t site_incoming(void *sst, struct buffer_if *buf,
/* If the source is our current peer then initiate a key setup,
because our peer's forgotten the key */
if (get_uint32(buf->start+4)==st->current.remote_session_id) {
- initiate_key_setup(st,"received a NAK");
+ bool_t initiated;
+ initiated = initiate_key_setup(st,"received a NAK",0);
+ if (!initiated) generate_send_prod(st,source);
} else {
slog(st,LOG_SEC,"bad incoming NAK");
}
@@ -1531,6 +1584,8 @@ static list_t *site_apply(closure_t *self, struct cloc loc, dict_t *context,
st->log_events=string_list_to_word(dict_lookup(dict,"log-events"),
log_event_table,"site");
+ st->allow_send_prod=0;
+
st->tunname=safe_malloc(strlen(st->localname)+strlen(st->remotename)+5,
"site_apply");
sprintf(st->tunname,"%s<->%s",st->localname,st->remotename);
@@ -1687,23 +1742,30 @@ static void transport_record_peer(struct site *st, transport_peers *peers,
}
static bool_t transport_compute_setupinit_peers(struct site *st,
- const struct comm_addr *configured_addr /* 0 if none or not found */) {
+ const struct comm_addr *configured_addr /* 0 if none or not found */,
+ const struct comm_addr *prod_hint_addr /* 0 if none */) {
- if (!configured_addr && !transport_peers_valid(&st->peers))
+ if (!configured_addr && !prod_hint_addr &&
+ !transport_peers_valid(&st->peers))
return False;
slog(st,LOG_SETUP_INIT,
- (!configured_addr ? "using only %d old peer address(es)"
- : "using configured address, and/or perhaps %d old peer address(es)"),
+ "using:%s%s %d old peer address(es)",
+ configured_addr ? " configured address;" : "",
+ prod_hint_addr ? " PROD hint address;" : "",
st->peers);
/* Non-mobile peers havve st->peers.npeers==0 or ==1, since they
* have transport_peers_max==1. The effect is that this code
* always uses the configured address if supplied, or otherwise
- * the existing data peer if one exists; this is as desired. */
+ * the address of the incoming PROD, or the existing data peer if
+ * one exists; this is as desired. */
transport_peers_copy(st,&st->setup_peers,&st->peers);
+ if (prod_hint_addr)
+ transport_record_peer(st,&st->setup_peers,prod_hint_addr,"prod");
+
if (configured_addr)
transport_record_peer(st,&st->setup_peers,configured_addr,"setupinit");
diff --git a/udp.c b/udp.c
index 77be5b1..5d1ef7c 100644
--- a/udp.c
+++ b/udp.c
@@ -19,6 +19,7 @@
#include <netinet/in.h>
#include <arpa/inet.h>
#include "util.h"
+#include "magic.h"
#include "unaligned.h"
#include "ipaddr.h"
#include "magic.h"
--
1.7.2.5
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