[Openvpn-devel] [M] Change in openvpn[master]: oob: Answer SERVER_PROBE on the server (P_CONTROL_OOB_V1)
"stipa \(Code Review\) via Openvpn-devel" <[email protected]> Wed, 29 Jul 2026 12:22:54 +0000
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Attention is currently required from: flichtenheld, plaisthos=2E
Hello pla=
isthos,
I'd like you to reexamine a change=2E Please visit
http://ge=
rrit=2Eopenvpn=2Enet/c/openvpn/+/1744?usp=3Demail
to look at the new patch=
set (#10)=2E
Change subject: oob: Answer SERVER_PROBE on the server (P_C=
ONTROL_OOB_V1)
=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=
=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=
=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=2E=
oob: Answer SERVER_PROBE on the server (P_CONTROL_OOB_V1)
Make a --mode =
server UDP listener answer an out-of-band SERVER_PROBE without
creating a s=
ession, so probing costs the server no state:
- tls_pre_decrypt_lite() a=
ccepts P_CONTROL_OOB_V1 and returns the new
VERDICT_VALID_OOB_V1 verdic=
t=2E
- tls_wrap_oob_standalone() builds a session-less P_CONTROL_OOB_V1 p=
acket:
opcode + session id + the usual tls-auth/tls-crypt wrapping arou=
nd a bare
TLV payload (no reliability/ACK fields), mirroring tls_reset_=
standalone()=2E
- oob_client_reply_write() writes the PROBE_REPLY message=
(message-type
header + probe_reply TLV)=2E
- do_pre_decrypt_check() =
handles the new verdict: it asks
oob_build_probe_reply() whether to ans=
wer, and if so sends a PROBE_REPLY
via send_probe_reply() (synchronous,=
stateless, like the HMAC reset path)
and returns false so no session i=
s created=2E The verdict joins the reset
verdicts in the reflect_filter=
rate-limit check, so a probe flood is capped
like a reset flood=2E
Th=
e reply carries, as its own session id, the stateless SYN-cookie the three-=
way
handshake uses, so the server keeps nothing per probe and a client can =
later
reuse the reply as the server's reset=2E
Change-Id: I930d3789e0313aa=
0c3bc51ee5fd1d108343d59f0
Signed-off-by: Lev Stipakov <lev@openvpn=2Enet>
-=
--
M src/openvpn/mudp=2Ec
M src/openvpn/oob=2Ec
M src/openvpn/oob=2Eh
M src=
/openvpn/ssl_pkt=2Ec
M src/openvpn/ssl_pkt=2Eh
5 files changed, 118 inserti=
ons(+), 4 deletions(-)
git pull ssh://gerrit=2Eopenvpn=2Enet:29418/open=
vpn refs/changes/44/1744/10
diff --git a/src/openvpn/mudp=2Ec b/src/openvp=
n/mudp=2Ec
index 2be085f=2E=2E2209407 100644
--- a/src/openvpn/mudp=2Ec
+++=
b/src/openvpn/mudp=2Ec
@@ -32,6 +32,7 @@
#include "memdbg=2Eh"
#includ=
e "ssl_pkt=2Eh"
+#include "oob=2Eh"
#ifdef HAVE_SYS_INOTIFY_H
#include =
<sys/inotify=2Eh>
@@ -87,6 +88,34 @@
"Reset pack=
et from client, sending HMAC based reset challenge", sock);
}
+/* Send a=
n out-of-band PROBE_REPLY back to the source of a SERVER_PROBE,
+ * synchro=
nously and without keeping any state, mirroring the reset path=2E */
+stati=
c void
+send_probe_reply(struct multi_context *m, struct tls_pre_decrypt_st=
ate *state,
+ struct tls_auth_standalone *tas, const struct=
oob_probe_reply *reply,
+ struct session_id *own_sid, stru=
ct link_socket *sock)
+{
+ struct gc_arena gc =3D gc_new();
+
+ /* Bu=
ild the payload of the reply (message-type header + probe_reply TLV) */
+ =
struct buffer payload =3D alloc_buf_gc(128, &gc);
+ if (!oob_client_re=
ply_write(&payload, reply))
+ {
+ gc_free(&gc);
+ return;
=
+ }
+
+ /* OOB replies use the same control-channel wrapping as the r=
equest */
+ reset_packet_id_send(&state->tls_wrap_tmp=2Eopt=2Epacket_id=
=2Esend);
+ state->tls_wrap_tmp=2Eopt=2Epacket_id=2Erec=2Einitialized =
=3D true;
+
+ struct buffer buf =3D tls_wrap_oob_standalone(&state->tls_=
wrap_tmp, tas, own_sid, &payload);
+ send_standalone_reply(m, &buf, "Ser=
ver Probe", "Server probe from client, sending probe reply",
+ =
sock);
+
+ gc_free(&gc);
+}
+
/* Returns true if this pa=
cket should create a new session */
static bool
@@ -105,7 +134,8 @@
s=
truct openvpn_sockaddr *from =3D &m->top=2Ec2=2Efrom=2Edest;
int handw=
indow =3D m->top=2Eoptions=2Ehandshake_window;
- if (verdict =3D=3D VE=
RDICT_VALID_RESET_V3 || verdict =3D=3D VERDICT_VALID_RESET_V2)
+ if (ver=
dict =3D=3D VERDICT_VALID_RESET_V3 || verdict =3D=3D VERDICT_VALID_RESET_V2=
+ || verdict =3D=3D VERDICT_VALID_OOB_V1)
{
/* Check =
if we are still below our limit for sending out
* responses */
@@=
-203,6 +233,31 @@
return ret;
}
+ else if (verdict =3D=
=3D VERDICT_VALID_OOB_V1)
+ {
+ /* Out-of-band server probe=2E st=
ate->newbuf points at the TLV payload
+ * (read_control_auth has st=
ripped the opcode, session id and any
+ * tls-auth/tls-crypt wrappi=
ng)=2E Answer it without creating a session=2E */
+ struct oob_probe=
_reply reply;
+ if (!oob_build_probe_reply(&state->newbuf, (uint64_t=
)now, (uint64_t)handwindow,
+ &state->pee=
r_session_id, &reply))
+ {
+ /* malformed or replayed/sta=
le probe: silently drop */
+ return false;
+ }
+
+ =
/* Our session id is a stateless SYN cookie (the same HMAC the three-way
+=
* handshake uses): we keep no per-probe state, and the reply can l=
ater
+ * also serve as the server's CONTROL_HARD_RESET_SERVER_V2, s=
o a client
+ * can start the handshake from it (the connect_lifetim=
e advertisement)=2E */
+ struct session_id sid =3D
+ calc=
ulate_session_id_hmac(state->peer_session_id, from, hmac, handwindow, 0);
+=
+ send_probe_reply(m, state, tas, &reply, &sid, sock);
+
+ /=
* An OOB probe never creates a session */
+ return false;
+ }
=
/* VERDICT_INVALID */
return false;
diff --git a/src/openvpn/oob=
=2Ec b/src/openvpn/oob=2Ec
index 930b213=2E=2Ec841d59 100644
--- a/src/open=
vpn/oob=2Ec
+++ b/src/openvpn/oob=2Ec
@@ -106,6 +106,12 @@
}
bool
+oob_=
client_reply_write(struct buffer *buf, const struct oob_probe_reply *reply)=
+{
+ return buf_write_u16(buf, OOB_MSG_PROBE_REPLY) && oob_probe_reply_=
write(buf, reply);
+}
+
+bool
oob_timestamp_in_window(uint64_t probe_ts, u=
int64_t now, uint64_t window_secs)
{
uint64_t diff =3D (now > probe_t=
s) ? (now - probe_ts) : (probe_ts - now);
diff --git a/src/openvpn/oob=2Eh =
b/src/openvpn/oob=2Eh
index 1afabbd=2E=2E49d64e8 100644
--- a/src/openvpn/o=
ob=2Eh
+++ b/src/openvpn/oob=2Eh
@@ -126,6 +126,12 @@
bool oob_server_prob=
e_read(struct buffer *payload, struct oob_probe_parameter *param);
/**
+=
* Write a complete PROBE_REPLY message (message-type header + probe_reply =
TLV)
+ * to buf=2E Sent by the server=2E
+ */
+bool oob_client_reply_write(=
struct buffer *buf, const struct oob_probe_reply *reply);
+
+/**
* Check =
whether a probe timestamp is within an acceptable window around the
* cur=
rent time=2E Used to cheaply drop replayed or implausibly-timed probes
* =
before doing any further work (see the probe_parameter timestamp rationale
=
diff --git a/src/openvpn/ssl_pkt=2Ec b/src/openvpn/ssl_pkt=2Ec
index 0d882d=
9=2E=2E335e26f 100644
--- a/src/openvpn/ssl_pkt=2Ec
+++ b/src/openvpn/ssl_p=
kt=2Ec
@@ -313,7 +313,8 @@
/* Allow only the reset packet or the fir=
st packet of the actual handshake=2E */
if (op !=3D P_CONTROL_HARD_RES=
ET_CLIENT_V2 && op !=3D P_CONTROL_HARD_RESET_CLIENT_V3
- && op !=3D =
P_CONTROL_V1 && op !=3D P_CONTROL_WKC_V1 && op !=3D P_ACK_V1)
+ && o=
p !=3D P_CONTROL_V1 && op !=3D P_CONTROL_WKC_V1 && op !=3D P_ACK_V1
+ =
&& !opcode_is_oob(op))
{
/*
* This can occur due =
to bogus data or DoS packets=2E
@@ -388,6 +389,10 @@
{
return=
VERDICT_VALID_WKC_V1;
}
+ else if (opcode_is_oob(op))
+ {
+ =
return VERDICT_VALID_OOB_V1;
+ }
else
{
return VE=
RDICT_VALID_RESET_V2;
@@ -442,6 +447,29 @@
return buf;
}
+struct bu=
ffer
+tls_wrap_oob_standalone(struct tls_wrap_ctx *ctx, struct tls_auth_sta=
ndalone *tas,
+ struct session_id *own_sid, const st=
ruct buffer *payload)
+{
+ /* Copy buffer here to point at the same data=
but allow tls_wrap_control
+ * to potentially change buf to point to a=
nother buffer without
+ * modifying the buffer in tas */
+ struct bu=
ffer buf =3D tas->workbuf;
+ ASSERT(buf_init(&buf, tas->frame=2Ebuf=2Ehe=
adroom));
+
+ /* Out-of-band messages carry the payload directly, with n=
o reliability
+ * or ACK fields=2E */
+ ASSERT(buf_copy(&buf, payloa=
d));
+
+ uint8_t header =3D (uint8_t)(P_CONTROL_OOB_V1 << P_OPCODE_SHIFT=
);
+
+ /* Add tls-auth/tls-crypt wrapping, this might replace buf with
+=
* ctx->work */
+ tls_wrap_control(ctx, header, &buf, own_sid);
+
+ =
return buf;
+}
+
hmac_ctx_t *
session_id_hmac_init(void)
{
diff --git=
a/src/openvpn/ssl_pkt=2Eh b/src/openvpn/ssl_pkt=2Eh
index 25e50bf=2E=2E3ab=
09db 100644
--- a/src/openvpn/ssl_pkt=2Eh
+++ b/src/openvpn/ssl_pkt=2Eh
@@ =
-62,8 +62,9 @@
* control channel session (e=2Eg=2E a server probe)=2E Inh=
erently unreliable:
* there is no protocol-level retransmission=2E
*
- =
* It is not legal on an established session; see opcode_valid_in_session()
=
- * below=2E */
+ * On the server this is accepted via the tls_pre_decrypt_=
lite() allowlist and
+ * handled in the new-connection path (it never creat=
es a session)=2E It is not
+ * legal on an established session; see opcode_=
valid_in_session() below=2E */
#define P_CONTROL_OOB_V1 12
/* define th=
e range of defined opcodes, in- and out-of-band=2E Note this is not
@@ -136=
,6 +137,9 @@
VERDICT_VALID_ACK_V1,
/** The packet is a valid cont=
rol packet with appended wrapped client key */
VERDICT_VALID_WKC_V1,
+=
/** This packet is a valid out-of-band control message (e=2Eg=2E a serv=
er
+ * probe)=2E It does not belong to a session and must not create on=
e=2E */
+ VERDICT_VALID_OOB_V1,
/** the packet failed on of the var=
ious checks */
VERDICT_INVALID
};
@@ -264,6 +268,21 @@
=
struct session_id *own_sid, struct session_id *remote=
_sid,
uint8_t header, bool request_rese=
nd_wkc);
+/**
+ * Wrap an already-built out-of-band payload (e=2Eg=2E pro=
be-reply TLVs) into a
+ * standalone, session-less P_CONTROL_OOB_V1 packet:=
it prepends the opcode and
+ * own_sid and applies the same tls-auth/tls-c=
rypt wrapping as a regular
+ * control packet, but carries no reliability/A=
CK fields=2E
+ *
+ * @param ctx tls wrapping context (from the pre-de=
crypt state)
+ * @param tas standalone auth context providing the wor=
k buffer
+ * @param own_sid session id to use as our session id in the he=
ader
+ * @param payload the OOB message payload (TLV stream) to wrap
+ * =
@return the wrapped packet buffer, ready to send
+ */
+struct buff=
er tls_wrap_oob_standalone(struct tls_wrap_ctx *ctx, struct tls_auth_standa=
lone *tas,
+ struct session_id *own_si=
d, const struct buffer *payload);
+
/**
* Extracts a control channel m=
essage from buf and adjusts the size of
--
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=2Eopenvpn=2Enet/c/openvpn/+/1744?usp=3Demail
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il
Gerrit-MessageType: newpatchset
Gerrit-Project: openvpn
Gerrit-Branch: =
master
Gerrit-Change-Id: I930d3789e0313aa0c3bc51ee5fd1d108343d59f0
Gerrit-C=
hange-Number: 1744
Gerrit-PatchSet: 10
Gerrit-Owner: stipa <lstipakov@gmail=
=2Ecom>
Gerrit-Reviewer: plaisthos <arne-openvpn@rfc2549=2Eorg>
Gerrit-CC: =
flichtenheld <frank@lichtenheld=2Ecom>
Gerrit-CC: openvpn-devel <openvpn-de=
vel@lists=2Esourceforge=2Enet>
Gerrit-Attention: plaisthos <arne-openvpn@rf=
c2549=2Eorg>
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Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE html><html><head><style></style></head><body><p> Attention is cur=
rently required from: flichtenheld, plaisthos=2E </p>
<p>stipa <strong>uplo=
aded patch set #10</strong> to this change=2E</p><p><a href=3D"http://gerri=
t=2Eopenvpn=2Enet/c/openvpn/+/1744?usp=3Demail">View Change</a></p><pre cla=
ss=3D"blocks" style=3D"font-family: monospace,monospace; white-space: pre-w=
rap;">oob: Answer SERVER_PROBE on the server (P_CONTROL_OOB_V1)<br><br>Make=
a --mode server UDP listener answer an out-of-band SERVER_PROBE without<br=
>creating a session, so probing costs the server no state:<br><br> - tls_p=
re_decrypt_lite() accepts P_CONTROL_OOB_V1 and returns the new<br> VERDI=
CT_VALID_OOB_V1 verdict=2E<br> - tls_wrap_oob_standalone() builds a sessio=
n-less P_CONTROL_OOB_V1 packet:<br> opcode + session id + the usual tls-=
auth/tls-crypt wrapping around a bare<br> TLV payload (no reliability/AC=
K fields), mirroring tls_reset_standalone()=2E<br> - oob_client_reply_writ=
e() writes the PROBE_REPLY message (message-type<br> header + probe_repl=
y TLV)=2E<br> - do_pre_decrypt_check() handles the new verdict: it asks<br=
> oob_build_probe_reply() whether to answer, and if so sends a PROBE_REP=
LY<br> via send_probe_reply() (synchronous, stateless, like the HMAC res=
et path)<br> and returns false so no session is created=2E The verdict j=
oins the reset<br> verdicts in the reflect_filter rate-limit check, so a=
probe flood is capped<br> like a reset flood=2E<br><br>The reply carrie=
s, as its own session id, the stateless SYN-cookie the three-way<br>handsha=
ke uses, so the server keeps nothing per probe and a client can later<br>re=
use the reply as the server's reset=2E<br><br>Change-Id: I930d3789e0313=
aa0c3bc51ee5fd1d108343d59f0<br>Signed-off-by: Lev Stipakov <lev@openvpn=
=2Enet><br>---<br>M src/openvpn/mudp=2Ec<br>M src/openvpn/oob=2Ec<br>M s=
rc/openvpn/oob=2Eh<br>M src/openvpn/ssl_pkt=2Ec<br>M src/openvpn/ssl_pkt=2E=
h<br>5 files changed, 118 insertions(+), 4 deletions(-)<br><br></pre><pre c=
lass=3D"blocks" style=3D"font-family: monospace,monospace; white-space: pre=
-wrap;">git pull ssh://gerrit=2Eopenvpn=2Enet:29418/openvpn refs/changes/44=
/1744/10</pre><pre style=3D"font-family: monospace,monospace; white-space: =
pre-wrap;"><span>diff --git a/src/openvpn/mudp=2Ec b/src/openvpn/mudp=2Ec</=
span><br><span>index 2be085f=2E=2E2209407 100644</span><br><span>--- a/src/=
openvpn/mudp=2Ec</span><br><span>+++ b/src/openvpn/mudp=2Ec</span><br><span=
>@@ -32,6 +32,7 @@</span><br><span> </span><br><span> #include "memdbg=
=2Eh"</span><br><span> #include "ssl_pkt=2Eh"</span><br><spa=
n style=3D"color: hsl(120, 100%, 40%);">+#include "oob=2Eh"</span=
><br><span> </span><br><span> #ifdef HAVE_SYS_INOTIFY_H</span><br><span> #i=
nclude <sys/inotify=2Eh></span><br><span>@@ -87,6 +88,34 @@</span><br=
><span> "Reset packet from client, sending H=
MAC based reset challenge", sock);</span><br><span> }</span><br><span>=
</span><br><span style=3D"color: hsl(120, 100%, 40%);">+/* Send an out-of-=
band PROBE_REPLY back to the source of a SERVER_PROBE,</span><br><span styl=
e=3D"color: hsl(120, 100%, 40%);">+ * synchronously and without keeping any=
state, mirroring the reset path=2E */</span><br><span style=3D"color: hsl(=
120, 100%, 40%);">+static void</span><br><span style=3D"color: hsl(120, 100=
%, 40%);">+send_probe_reply(struct multi_context *m, struct tls_pre_decrypt=
_state *state,</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
struct tls_auth_standalone *tas, const struct oob_probe_reply *=
reply,</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
struct session_id *own_sid, struct link_socket *sock)</span><br><span s=
tyle=3D"color: hsl(120, 100%, 40%);">+{</span><br><span style=3D"color: hsl=
(120, 100%, 40%);">+ struct gc_arena gc =3D gc_new();</span><br><span st=
yle=3D"color: hsl(120, 100%, 40%);">+</span><br><span style=3D"color: hsl(1=
20, 100%, 40%);">+ /* Build the payload of the reply (message-type heade=
r + probe_reply TLV) */</span><br><span style=3D"color: hsl(120, 100%, 40%)=
;">+ struct buffer payload =3D alloc_buf_gc(128, &gc);</span><br><sp=
an style=3D"color: hsl(120, 100%, 40%);">+ if (!oob_client_reply_write(&=
amp;payload, reply))</span><br><span style=3D"color: hsl(120, 100%, 40%);">=
+ {</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ gc_fr=
ee(&gc);</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
return;</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ }</span=
><br><span style=3D"color: hsl(120, 100%, 40%);">+</span><br><span style=3D=
"color: hsl(120, 100%, 40%);">+ /* OOB replies use the same control-chan=
nel wrapping as the request */</span><br><span style=3D"color: hsl(120, 100=
%, 40%);">+ reset_packet_id_send(&state->tls_wrap_tmp=2Eopt=2Epac=
ket_id=2Esend);</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
state->tls_wrap_tmp=2Eopt=2Epacket_id=2Erec=2Einitialized =3D true;</spa=
n><br><span style=3D"color: hsl(120, 100%, 40%);">+</span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+ struct buffer buf =3D tls_wrap_oob_st=
andalone(&state->tls_wrap_tmp, tas, own_sid, &payload);</span><b=
r><span style=3D"color: hsl(120, 100%, 40%);">+ send_standalone_reply(m,=
&buf, "Server Probe", "Server probe from client, sendin=
g probe reply",</span><br><span style=3D"color: hsl(120, 100%, 40%);">=
+ sock);</span><br><span style=3D"color: hsl(120, =
100%, 40%);">+</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ g=
c_free(&gc);</span><br><span style=3D"color: hsl(120, 100%, 40%);">+}</=
span><br><span style=3D"color: hsl(120, 100%, 40%);">+</span><br><span> </s=
pan><br><span> /* Returns true if this packet should create a new session *=
/</span><br><span> static bool</span><br><span>@@ -105,7 +134,8 @@</span><b=
r><span> struct openvpn_sockaddr *from =3D &m->top=2Ec2=2Efrom=
=2Edest;</span><br><span> int handwindow =3D m->top=2Eoptions=2Ehand=
shake_window;</span><br><span> </span><br><span style=3D"color: hsl(0, 100%=
, 40%);">- if (verdict =3D=3D VERDICT_VALID_RESET_V3 || verdict =3D=3D V=
ERDICT_VALID_RESET_V2)</span><br><span style=3D"color: hsl(120, 100%, 40%);=
">+ if (verdict =3D=3D VERDICT_VALID_RESET_V3 || verdict =3D=3D VERDICT_=
VALID_RESET_V2</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
|| verdict =3D=3D VERDICT_VALID_OOB_V1)</span><br><span> {</span><br=
><span> /* Check if we are still below our limit for sending out</s=
pan><br><span> * responses */</span><br><span>@@ -203,6 +233,31 @@=
</span><br><span> </span><br><span> return ret;</span><br><span> =
}</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ else if (ver=
dict =3D=3D VERDICT_VALID_OOB_V1)</span><br><span style=3D"color: hsl(120, =
100%, 40%);">+ {</span><br><span style=3D"color: hsl(120, 100%, 40%);">+=
/* Out-of-band server probe=2E state->newbuf points at the TLV p=
ayload</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * (r=
ead_control_auth has stripped the opcode, session id and any</span><br><spa=
n style=3D"color: hsl(120, 100%, 40%);">+ * tls-auth/tls-crypt wrap=
ping)=2E Answer it without creating a session=2E */</span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+ struct oob_probe_reply reply;</sp=
an><br><span style=3D"color: hsl(120, 100%, 40%);">+ if (!oob_build_=
probe_reply(&state->newbuf, (uint64_t)now, (uint64_t)handwindow,</sp=
an><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
&state->peer_session_id, &reply))</span><br><span st=
yle=3D"color: hsl(120, 100%, 40%);">+ {</span><br><span style=3D"col=
or: hsl(120, 100%, 40%);">+ /* malformed or replayed/stale probe=
: silently drop */</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
return false;</span><br><span style=3D"color: hsl(120, 100%, 40%=
);">+ }</span><br><span style=3D"color: hsl(120, 100%, 40%);">+</spa=
n><br><span style=3D"color: hsl(120, 100%, 40%);">+ /* Our session i=
d is a stateless SYN cookie (the same HMAC the three-way</span><br><span st=
yle=3D"color: hsl(120, 100%, 40%);">+ * handshake uses): we keep no=
per-probe state, and the reply can later</span><br><span style=3D"color: h=
sl(120, 100%, 40%);">+ * also serve as the server's CONTROL_HAR=
D_RESET_SERVER_V2, so a client</span><br><span style=3D"color: hsl(120, 100=
%, 40%);">+ * can start the handshake from it (the connect_lifetime=
advertisement)=2E */</span><br><span style=3D"color: hsl(120, 100%, 40%);"=
>+ struct session_id sid =3D</span><br><span style=3D"color: hsl(120=
, 100%, 40%);">+ calculate_session_id_hmac(state->peer_sessio=
n_id, from, hmac, handwindow, 0);</span><br><span style=3D"color: hsl(120, =
100%, 40%);">+</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
send_probe_reply(m, state, tas, &reply, &sid, sock);</span><br><=
span style=3D"color: hsl(120, 100%, 40%);">+</span><br><span style=3D"color=
: hsl(120, 100%, 40%);">+ /* An OOB probe never creates a session */=
</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ return fals=
e;</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ }</span><br><=
span> </span><br><span> /* VERDICT_INVALID */</span><br><span> retu=
rn false;</span><br><span>diff --git a/src/openvpn/oob=2Ec b/src/openvpn/oo=
b=2Ec</span><br><span>index 930b213=2E=2Ec841d59 100644</span><br><span>---=
a/src/openvpn/oob=2Ec</span><br><span>+++ b/src/openvpn/oob=2Ec</span><br>=
<span>@@ -106,6 +106,12 @@</span><br><span> }</span><br><span> </span><br><=
span> bool</span><br><span style=3D"color: hsl(120, 100%, 40%);">+oob_clien=
t_reply_write(struct buffer *buf, const struct oob_probe_reply *reply)</spa=
n><br><span style=3D"color: hsl(120, 100%, 40%);">+{</span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+ return buf_write_u16(buf, OOB_MSG_PRO=
BE_REPLY) && oob_probe_reply_write(buf, reply);</span><br><span sty=
le=3D"color: hsl(120, 100%, 40%);">+}</span><br><span style=3D"color: hsl(1=
20, 100%, 40%);">+</span><br><span style=3D"color: hsl(120, 100%, 40%);">+b=
ool</span><br><span> oob_timestamp_in_window(uint64_t probe_ts, uint64_t no=
w, uint64_t window_secs)</span><br><span> {</span><br><span> uint64_t d=
iff =3D (now > probe_ts) ? (now - probe_ts) : (probe_ts - now);</span><b=
r><span>diff --git a/src/openvpn/oob=2Eh b/src/openvpn/oob=2Eh</span><br><s=
pan>index 1afabbd=2E=2E49d64e8 100644</span><br><span>--- a/src/openvpn/oob=
=2Eh</span><br><span>+++ b/src/openvpn/oob=2Eh</span><br><span>@@ -126,6 +1=
26,12 @@</span><br><span> bool oob_server_probe_read(struct buffer *payload=
, struct oob_probe_parameter *param);</span><br><span> </span><br><span> /*=
*</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * Write a complet=
e PROBE_REPLY message (message-type header + probe_reply TLV)</span><br><sp=
an style=3D"color: hsl(120, 100%, 40%);">+ * to buf=2E Sent by the server=
=2E</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ */</span><br><s=
pan style=3D"color: hsl(120, 100%, 40%);">+bool oob_client_reply_write(stru=
ct buffer *buf, const struct oob_probe_reply *reply);</span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+</span><br><span style=3D"color: hsl(120,=
100%, 40%);">+/**</span><br><span> * Check whether a probe timestamp is w=
ithin an acceptable window around the</span><br><span> * current time=2E U=
sed to cheaply drop replayed or implausibly-timed probes</span><br><span> =
* before doing any further work (see the probe_parameter timestamp rational=
e</span><br><span>diff --git a/src/openvpn/ssl_pkt=2Ec b/src/openvpn/ssl_pk=
t=2Ec</span><br><span>index 0d882d9=2E=2E335e26f 100644</span><br><span>---=
a/src/openvpn/ssl_pkt=2Ec</span><br><span>+++ b/src/openvpn/ssl_pkt=2Ec</s=
pan><br><span>@@ -313,7 +313,8 @@</span><br><span> </span><br><span> /*=
Allow only the reset packet or the first packet of the actual handshake=2E=
*/</span><br><span> if (op !=3D P_CONTROL_HARD_RESET_CLIENT_V2 &&a=
mp; op !=3D P_CONTROL_HARD_RESET_CLIENT_V3</span><br><span style=3D"color: =
hsl(0, 100%, 40%);">- && op !=3D P_CONTROL_V1 && op =
!=3D P_CONTROL_WKC_V1 && op !=3D P_ACK_V1)</span><br><span style=3D=
"color: hsl(120, 100%, 40%);">+ && op !=3D P_CONTROL_V1 &=
;& op !=3D P_CONTROL_WKC_V1 && op !=3D P_ACK_V1</span><br><span=
style=3D"color: hsl(120, 100%, 40%);">+ && !opcode_is_oob(o=
p))</span><br><span> {</span><br><span> /*</span><br><span> =
* This can occur due to bogus data or DoS packets=2E</span><br><span>=
@@ -388,6 +389,10 @@</span><br><span> {</span><br><span> return=
VERDICT_VALID_WKC_V1;</span><br><span> }</span><br><span style=3D"colo=
r: hsl(120, 100%, 40%);">+ else if (opcode_is_oob(op))</span><br><span s=
tyle=3D"color: hsl(120, 100%, 40%);">+ {</span><br><span style=3D"color:=
hsl(120, 100%, 40%);">+ return VERDICT_VALID_OOB_V1;</span><br><spa=
n style=3D"color: hsl(120, 100%, 40%);">+ }</span><br><span> else</s=
pan><br><span> {</span><br><span> return VERDICT_VALID_RESET_V2=
;</span><br><span>@@ -442,6 +447,29 @@</span><br><span> return buf;</sp=
an><br><span> }</span><br><span> </span><br><span style=3D"color: hsl(120, =
100%, 40%);">+struct buffer</span><br><span style=3D"color: hsl(120, 100%, =
40%);">+tls_wrap_oob_standalone(struct tls_wrap_ctx *ctx, struct tls_auth_s=
tandalone *tas,</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
struct session_id *own_sid, const struct buffer *payloa=
d)</span><br><span style=3D"color: hsl(120, 100%, 40%);">+{</span><br><span=
style=3D"color: hsl(120, 100%, 40%);">+ /* Copy buffer here to point at=
the same data but allow tls_wrap_control</span><br><span style=3D"color: h=
sl(120, 100%, 40%);">+ * to potentially change buf to point to another =
buffer without</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
* modifying the buffer in tas */</span><br><span style=3D"color: hsl(120, 1=
00%, 40%);">+ struct buffer buf =3D tas->workbuf;</span><br><span sty=
le=3D"color: hsl(120, 100%, 40%);">+ ASSERT(buf_init(&buf, tas->f=
rame=2Ebuf=2Eheadroom));</span><br><span style=3D"color: hsl(120, 100%, 40%=
);">+</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ /* Out-of-=
band messages carry the payload directly, with no reliability</span><br><sp=
an style=3D"color: hsl(120, 100%, 40%);">+ * or ACK fields=2E */</span>=
<br><span style=3D"color: hsl(120, 100%, 40%);">+ ASSERT(buf_copy(&b=
uf, payload));</span><br><span style=3D"color: hsl(120, 100%, 40%);">+</spa=
n><br><span style=3D"color: hsl(120, 100%, 40%);">+ uint8_t header =3D (=
uint8_t)(P_CONTROL_OOB_V1 << P_OPCODE_SHIFT);</span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+</span><br><span style=3D"color: hsl(120,=
100%, 40%);">+ /* Add tls-auth/tls-crypt wrapping, this might replace b=
uf with</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * ctx-&=
gt;work */</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ tls_w=
rap_control(ctx, header, &buf, own_sid);</span><br><span style=3D"color=
: hsl(120, 100%, 40%);">+</span><br><span style=3D"color: hsl(120, 100%, 40=
%);">+ return buf;</span><br><span style=3D"color: hsl(120, 100%, 40%);"=
>+}</span><br><span style=3D"color: hsl(120, 100%, 40%);">+</span><br><span=
> hmac_ctx_t *</span><br><span> session_id_hmac_init(void)</span><br><span>=
{</span><br><span>diff --git a/src/openvpn/ssl_pkt=2Eh b/src/openvpn/ssl_p=
kt=2Eh</span><br><span>index 25e50bf=2E=2E3ab09db 100644</span><br><span>--=
- a/src/openvpn/ssl_pkt=2Eh</span><br><span>+++ b/src/openvpn/ssl_pkt=2Eh</=
span><br><span>@@ -62,8 +62,9 @@</span><br><span> * control channel sessio=
n (e=2Eg=2E a server probe)=2E Inherently unreliable:</span><br><span> * t=
here is no protocol-level retransmission=2E</span><br><span> *</span><br><=
span style=3D"color: hsl(0, 100%, 40%);">- * It is not legal on an establis=
hed session; see opcode_valid_in_session()</span><br><span style=3D"color: =
hsl(0, 100%, 40%);">- * below=2E */</span><br><span style=3D"color: hsl(120=
, 100%, 40%);">+ * On the server this is accepted via the tls_pre_decrypt_l=
ite() allowlist and</span><br><span style=3D"color: hsl(120, 100%, 40%);">+=
* handled in the new-connection path (it never creates a session)=2E It is=
not</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * legal on an =
established session; see opcode_valid_in_session() below=2E */</span><br><s=
pan> #define P_CONTROL_OOB_V1 12</span><br><span> </span><br><span> /* defi=
ne the range of defined opcodes, in- and out-of-band=2E Note this is not</s=
pan><br><span>@@ -136,6 +137,9 @@</span><br><span> VERDICT_VALID_ACK_V1=
,</span><br><span> /** The packet is a valid control packet with append=
ed wrapped client key */</span><br><span> VERDICT_VALID_WKC_V1,</span><=
br><span style=3D"color: hsl(120, 100%, 40%);">+ /** This packet is a va=
lid out-of-band control message (e=2Eg=2E a server</span><br><span style=3D=
"color: hsl(120, 100%, 40%);">+ * probe)=2E It does not belong to a ses=
sion and must not create one=2E */</span><br><span style=3D"color: hsl(120,=
100%, 40%);">+ VERDICT_VALID_OOB_V1,</span><br><span> /** the packe=
t failed on of the various checks */</span><br><span> VERDICT_INVALID</=
span><br><span> };</span><br><span>@@ -264,6 +268,21 @@</span><br><span> =
struct session_id *own_sid, struct session=
_id *remote_sid,</span><br><span> uint8_=
t header, bool request_resend_wkc);</span><br><span> </span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+/**</span><br><span style=3D"color: hsl(1=
20, 100%, 40%);">+ * Wrap an already-built out-of-band payload (e=2Eg=2E pr=
obe-reply TLVs) into a</span><br><span style=3D"color: hsl(120, 100%, 40%);=
">+ * standalone, session-less P_CONTROL_OOB_V1 packet: it prepends the opc=
ode and</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * own_sid a=
nd applies the same tls-auth/tls-crypt wrapping as a regular</span><br><spa=
n style=3D"color: hsl(120, 100%, 40%);">+ * control packet, but carries no =
reliability/ACK fields=2E</span><br><span style=3D"color: hsl(120, 100%, 40=
%);">+ *</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * @param c=
tx tls wrapping context (from the pre-decrypt state)</span><br><span =
style=3D"color: hsl(120, 100%, 40%);">+ * @param tas standalone auth =
context providing the work buffer</span><br><span style=3D"color: hsl(120, =
100%, 40%);">+ * @param own_sid session id to use as our session id in th=
e header</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ * @param p=
ayload the OOB message payload (TLV stream) to wrap</span><br><span style=
=3D"color: hsl(120, 100%, 40%);">+ * @return the wrapped packet bu=
ffer, ready to send</span><br><span style=3D"color: hsl(120, 100%, 40%);">+=
*/</span><br><span style=3D"color: hsl(120, 100%, 40%);">+struct buffer tl=
s_wrap_oob_standalone(struct tls_wrap_ctx *ctx, struct tls_auth_standalone =
*tas,</span><br><span style=3D"color: hsl(120, 100%, 40%);">+ =
struct session_id *own_sid, const struct buffer *pa=
yload);</span><br><span style=3D"color: hsl(120, 100%, 40%);">+</span><br><=
span> </span><br><span> /**</span><br><span> * Extracts a control channel =
message from buf and adjusts the size of</span><br><span></span><br></pre><=
p>To view, visit <a href=3D"http://gerrit=2Eopenvpn=2Enet/c/openvpn/+/1744?=
usp=3Demail">change 1744</a>=2E To unsubscribe, or for help writing mail fi=
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<div style=3D"display:none"> Gerrit-MessageType: newpatchset=
</div>
<div style=3D"display:none"> Gerrit-Project: openvpn </div>
<div st=
yle=3D"display:none"> Gerrit-Branch: master </div>
<div style=3D"display:no=
ne"> Gerrit-Change-Id: I930d3789e0313aa0c3bc51ee5fd1d108343d59f0 </div>
<di=
v style=3D"display:none"> Gerrit-Change-Number: 1744 </div>
<div style=3D"d=
isplay:none"> Gerrit-PatchSet: 10 </div>
<div style=3D"display:none"> Gerri=
t-Owner: stipa <lstipakov@gmail=2Ecom> </div>
<div style=3D"display:n=
one"> Gerrit-Reviewer: plaisthos <arne-openvpn@rfc2549=2Eorg> </div>
=
<div style=3D"display:none"> Gerrit-CC: flichtenheld <frank@lichtenheld=
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<div style=3D"display:none"> Gerrit-CC: openvpn-devel <=
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