Attention is currently required from: flichtenheld.
plaisthos *uploaded patch set #3* to this change.
View Change <http://gerrit.openvpn.net/c/openvpn/+/1067?usp=email>
Check message id/acked ids too when doing sessionid cookie checks
This fixes that control packets on a floating client can trigger
creating a new session in special circumstances:
To trigger this circumstance a connection needs to
- starts on IP A
- successfully floats to IP B by data packet
- then has a control packet from IP A before any
data packet can trigger the float back to IP A
and all of this needs to happen in the 60s time
that hmac cookie is valid in the default
configuration.
In this scenario we would trigger a new connection as the HMAC
session id would be valid.
This patch adds checking also of the message-id and acked ids to
discern packet from the initial three-way handshake where these
ids 0 or 1 from any later packet.
This will now trigger (at verb 4 or higher) a messaged like:
Packet (P_ACK_V1) with invalid or missing SID
instead.
Reported-By: Walter Doekes <walter.open...@wjd.nu>
Tested-By: Walter Doekes <walter.open...@wjd.nu>
Change-Id: I6752dcd5aff3e5cea2b439366479e86751a1c403
Signed-off-by: Arne Schwabe <a...@rfc2549.org>
---
M src/openvpn/mudp.c
M src/openvpn/ssl_pkt.c
M src/openvpn/ssl_pkt.h
M tests/unit_tests/openvpn/test_pkt.c
4 files changed, 112 insertions(+), 6 deletions(-)
git pull ssh://gerrit.openvpn.net:29418/openvpn refs/changes/67/1067/3
diff --git a/src/openvpn/mudp.c b/src/openvpn/mudp.c
index 93e65e0..9cd667c 100644
--- a/src/openvpn/mudp.c
+++ b/src/openvpn/mudp.c
@@ -63,7 +63,6 @@
msg(D_MULTI_DEBUG, "Reset packet from client, sending HMAC based reset
challenge");
}
-
/* Returns true if this packet should create a new session */
static bool
do_pre_decrypt_check(struct multi_context *m,
@@ -155,7 +154,8 @@
* need to contain the peer id */
struct gc_arena gc = gc_new();
- bool ret = check_session_id_hmac(state, from, hmac, handwindow);
+ bool pkt_is_ack = (verdict == VERDICT_VALID_ACK_V1);
+ bool ret = check_session_id_hmac(state, from, hmac, handwindow,
pkt_is_ack);
const char *peer = print_link_socket_actual(&m->top.c2.from, &gc);
uint8_t pkt_firstbyte = *BPTR( &m->top.c2.buf);
@@ -171,6 +171,7 @@
msg(D_MULTI_DEBUG, "Valid packet (%s) with HMAC challenge from peer (%s), "
"accepting new connection.", packet_opcode_name(op), peer);
}
+
gc_free(&gc);
return ret;
diff --git a/src/openvpn/ssl_pkt.c b/src/openvpn/ssl_pkt.c
index bfd405f..0bbc465 100644
--- a/src/openvpn/ssl_pkt.c
+++ b/src/openvpn/ssl_pkt.c
@@ -293,6 +293,7 @@
}
}
+
/*
* This function is similar to tls_pre_decrypt, except it is called
* when we are in server mode and receive an initial incoming
@@ -530,7 +531,8 @@
check_session_id_hmac(struct tls_pre_decrypt_state *state,
const struct openvpn_sockaddr *from,
hmac_ctx_t *hmac,
- int handwindow)
+ int handwindow,
+ bool pkt_is_ack)
{
if (!from)
{
@@ -545,6 +547,36 @@
return false;
}
+ /* Check if the packet ID of the packet or ACKED packet is <= 1 */
+ for (int i = 0; i < ack.len; i++)
+ {
+ /* This packet ACKs a packet that has a higher packet id than the
+ * ones expected in the three-way handshake, consider it as invalid
+ * for the session */
+ if (ack.packet_id[i] > 1)
+ {
+ return false;
+ }
+ }
+
+ if (!pkt_is_ack)
+ {
+ packet_id_type message_id;
+ /* Extract the packet ID from the packet */
+ if (!reliable_ack_read_packet_id(&buf, &message_id))
+ {
+ return false;
+ }
+
+ /* similar check. Anything larger than 1 is not considered part of the
+ * three-way handshake */
+ if (message_id > 1)
+ {
+ return false;
+ }
+ }
+
+
/* check adjacent timestamps too */
for (int offset = -2; offset <= 1; offset++)
{
diff --git a/src/openvpn/ssl_pkt.h b/src/openvpn/ssl_pkt.h
index 98a39d3..1b6bcc0 100644
--- a/src/openvpn/ssl_pkt.h
+++ b/src/openvpn/ssl_pkt.h
@@ -180,17 +180,24 @@
/**
* Checks if a control packet has a correct HMAC server session id
*
+ * This will also consider packets that have a packet id higher
+ * than 1 or ack packets higher than 1 to be invalid as they are
+ * not part of the initial three way handshake of OpenVPN and should
+ * not create a new connection.
+ *
* @param state session information
* @param from link_socket from the client
* @param hmac the hmac context to use for the calculation
* @param handwindow the quantisation of the current time
+ * @param pkt_is_ack the packet being checked is a P_ACK_V1
* @return the expected server session id
*/
bool
check_session_id_hmac(struct tls_pre_decrypt_state *state,
const struct openvpn_sockaddr *from,
hmac_ctx_t *hmac,
- int handwindow);
+ int handwindow,
+ bool pkt_is_ack);
/*
* Write a control channel authentication record.
diff --git a/tests/unit_tests/openvpn/test_pkt.c
b/tests/unit_tests/openvpn/test_pkt.c
index ebffabe..56ed842 100644
--- a/tests/unit_tests/openvpn/test_pkt.c
+++ b/tests/unit_tests/openvpn/test_pkt.c
@@ -170,6 +170,27 @@
0x85, 0xdb, 0x53, 0x56, 0x23, 0xb0, 0x2e
};
+/* no tls-auth, P_ACK_V1, acks 0,1, and 2 */
+const uint8_t client_ack_123_none_random_id[] = {
+ 0x28,
+ 0xae, 0xb9, 0xaf, 0xe1, 0xf0, 0x1d, 0x79, 0xc8,
+ 0x03,
+ 0x00, 0x00, 0x00, 0x00,
+ 0x00, 0x00, 0x00, 0x01,
+ 0x00, 0x00, 0x00, 0x02,
+ 0xdd, 0x85, 0xdb, 0x53, 0x56, 0x23, 0xb0, 0x2e
+};
+
+/* no tls-auth, P_CONTROL_V1, acks 0, msg-id 2 */
+const uint8_t client_control_none_random_id[] = {
+ 0x20,
+ 0xae, 0xb9, 0xaf, 0xe1, 0xf0, 0x1d, 0x79, 0xc8,
+ 0x01,
+ 0x00, 0x00, 0x00, 0x00,
+ 0x02
+};
+
+
struct tls_auth_standalone
init_tas_auth(int key_direction)
{
@@ -439,7 +460,7 @@
assert_int_equal(verdict, VERDICT_VALID_CONTROL_V1);
/* This is a valid packet but containing a random id instead of an HMAC id*/
- bool valid = check_session_id_hmac(&state, &from.dest, hmac, 30);
+ bool valid = check_session_id_hmac(&state, &from.dest, hmac, 30, false);
assert_false(valid);
free_tls_pre_decrypt_state(&state);
@@ -470,7 +491,7 @@
verdict = tls_pre_decrypt_lite(&tas, &state, &from, &buf);
assert_int_equal(verdict, VERDICT_VALID_ACK_V1);
- bool valid = check_session_id_hmac(&state, &from.dest, hmac, 30);
+ bool valid = check_session_id_hmac(&state, &from.dest, hmac, 30, true);
assert_true(valid);
free_tls_pre_decrypt_state(&state);
@@ -479,6 +500,50 @@
hmac_ctx_free(hmac);
}
+static void
+test_verify_hmac_none_out_of_range_ack(void **ut_state)
+{
+ hmac_ctx_t *hmac = session_id_hmac_init();
+
+ struct link_socket_actual from = { 0 };
+ from.dest.addr.sa.sa_family = AF_INET;
+
+ struct tls_auth_standalone tas = { 0 };
+ struct tls_pre_decrypt_state state = { 0 };
+
+ struct buffer buf = alloc_buf(1024);
+ enum first_packet_verdict verdict;
+
+ tas.tls_wrap.mode = TLS_WRAP_NONE;
+
+ buf_reset_len(&buf);
+ buf_write(&buf, client_ack_123_none_random_id,
sizeof(client_ack_123_none_random_id));
+
+
+ verdict = tls_pre_decrypt_lite(&tas, &state, &from, &buf);
+ assert_int_equal(verdict, VERDICT_VALID_ACK_V1);
+
+ /* should fail because it acks 2 */
+ bool valid = check_session_id_hmac(&state, &from.dest, hmac, 30, true);
+ assert_false(valid);
+
+ /* Try test with the control with a too high message id now */
+ buf_reset_len(&buf);
+ buf_write(&buf, client_control_none_random_id,
sizeof(client_control_none_random_id));
+
+ verdict = tls_pre_decrypt_lite(&tas, &state, &from, &buf);
+ assert_int_equal(verdict, VERDICT_VALID_CONTROL_V1);
+
+ /* should fail because it has message id 2 */
+ valid = check_session_id_hmac(&state, &from.dest, hmac, 30, true);
+ assert_false(valid);
+
+ free_tls_pre_decrypt_state(&state);
+ free_buf(&buf);
+ hmac_ctx_cleanup(hmac);
+ hmac_ctx_free(hmac);
+}
+
static hmac_ctx_t *
init_static_hmac(void)
{
@@ -667,6 +732,7 @@
cmocka_unit_test(test_calc_session_id_hmac_static),
cmocka_unit_test(test_verify_hmac_none),
cmocka_unit_test(test_verify_hmac_tls_auth),
+ cmocka_unit_test(test_verify_hmac_none_out_of_range_ack),
cmocka_unit_test(test_generate_reset_packet_plain),
cmocka_unit_test(test_generate_reset_packet_tls_auth),
cmocka_unit_test(test_extract_control_message)
To view, visit change 1067
<http://gerrit.openvpn.net/c/openvpn/+/1067?usp=email>. To unsubscribe,
or for help writing mail filters, visit settings
<http://gerrit.openvpn.net/settings>.
Gerrit-Project: openvpn
Gerrit-Branch: master
Gerrit-Change-Id: I6752dcd5aff3e5cea2b439366479e86751a1c403
Gerrit-Change-Number: 1067
Gerrit-PatchSet: 3
Gerrit-Owner: plaisthos <arne-open...@rfc2549.org>
Gerrit-Reviewer: flichtenheld <fr...@lichtenheld.com>
Gerrit-CC: openvpn-devel <openvpn-devel@lists.sourceforge.net>
Gerrit-Attention: flichtenheld <fr...@lichtenheld.com>
Gerrit-MessageType: newpatchset
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