From 62e75d8830eb56ab03bd4689d51ffd6d4150f461 Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Sat, 11 Feb 2023 23:21:00 +0000
Subject: implemented per-packet HMAC to avoid MITM tampering.

---
 dat.h      |  5 ++++-
 fmt.c      | 25 +++++++++++++++++++++++++
 fns.h      |  7 +++++++
 mkfile     |  1 +
 musw.c     | 29 +++++++++++++++++++----------
 muswd.c    | 35 +++++++++++++++++++++--------------
 net.c      | 37 +++++++++++++++++++++++++++++++++++++
 pack.c     |  4 ++++
 party.c    |  2 ++
 physics.c  |  2 ++
 sprite.c   |  2 ++
 universe.c |  2 ++
 12 files changed, 126 insertions(+), 25 deletions(-)
 create mode 100644 fmt.c

diff --git a/dat.h b/dat.h
index 89554bc..566c248 100644
--- a/dat.h
+++ b/dat.h
@@ -46,7 +46,7 @@ enum {
 
 enum {
 	ProtocolID	= 0x5753554d,	/* MUSW */
-	Framehdrsize	= 4+1+4+4+2,
+	Framehdrsize	= 4+1+4+4+2+MD5dlen,
 	MTU		= 1024
 };
 
@@ -147,6 +147,7 @@ struct Frame
 	u32int seq;
 	u32int ack;
 	u16int len;
+	uchar sig[MD5dlen];
 	uchar data[];
 };
 
@@ -177,3 +178,5 @@ struct Party
 	Universe *u;
 	Party *prev, *next;
 };
+
+#pragma varargck type "Φ" Frame*
diff --git a/fmt.c b/fmt.c
new file mode 100644
index 0000000..7d33e57
--- /dev/null
+++ b/fmt.c
@@ -0,0 +1,25 @@
+#include <u.h>
+#include <libc.h>
+#include <ip.h>
+#include <mp.h>
+#include <libsec.h>
+#include <thread.h>
+#include <draw.h>
+#include <geometry.h>
+#include "dat.h"
+#include "fns.h"
+
+int
+Φfmt(Fmt *f)
+{
+	int n, i;
+	Frame *frame;
+
+	frame = va_arg(f->args, Frame*);
+
+	n = fmtprint(f, "id %x type %ud seq %ud ack %ud len %ud sig ",
+		frame->id, frame->type, frame->seq, frame->ack, frame->len);
+	for(i = 0; i < MD5dlen; i++)
+		n += fmtprint(f, "%2.2x", frame->sig[i]);
+	return n;
+}
diff --git a/fns.h b/fns.h
index b4059ce..6ec3b0d 100644
--- a/fns.h
+++ b/fns.h
@@ -53,4 +53,11 @@ ulong dhgenkey(ulong, ulong, ulong);
 NetConn *newnetconn(NCState, Udphdr*);
 void delnetconn(NetConn*);
 Frame *newframe(Frame*, u8int, u32int, u32int, u16int, uchar*);
+void signframe(Frame*, ulong);
+int verifyframe(Frame*, ulong);
 void delframe(Frame*);
+
+/*
+ * fmt
+ */
+int Φfmt(Fmt*);
diff --git a/mkfile b/mkfile
index 3d7da33..123c050 100644
--- a/mkfile
+++ b/mkfile
@@ -15,6 +15,7 @@ OFILES=\
 	universe.$O\
 	sprite.$O\
 	net.$O\
+	fmt.$O\
 
 HFILES=\
 	dat.h\
diff --git a/musw.c b/musw.c
index ca428bf..039f7b6 100644
--- a/musw.c
+++ b/musw.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <bio.h>
 #include <thread.h>
 #include <draw.h>
@@ -164,6 +166,7 @@ sendkeys(ulong kdown)
 
 	frame = newframe(nil, NCinput, 0, 0, sizeof(kdown), nil);
 	pack(frame->data, frame->len, "k", kdown);
+	signframe(frame, netconn.dh.priv);
 	sendp(egress, frame);
 }
 
@@ -241,9 +244,8 @@ threadnetrecv(void *arg)
 		if(debug){
 			rport = frame->udp.rport[0]<<8 | frame->udp.rport[1];
 			lport = frame->udp.lport[0]<<8 | frame->udp.lport[1];
-			fprint(2, "%I!%ud ← %I!%ud | rcvd type %ud seq %ud ack %ud len %ud\n",
-				frame->udp.laddr, lport, frame->udp.raddr, rport,
-				frame->type, frame->seq, frame->ack, frame->len);
+			fprint(2, "%I!%ud → %I!%ud | rcvd %Φ\n",
+				frame->udp.laddr, lport, frame->udp.raddr, rport, frame);
 		}
 	}
 	closeioproc(io);
@@ -267,27 +269,33 @@ threadnetppu(void *)
 				unpack(frame->data, frame->len, "kk", &netconn.dh.p, &netconn.dh.g);
 
 				newf = newframe(frame, NCdhx, 0, 0, sizeof(ulong), nil);
-	
+
 				netconn.dh.sec = truerand();
 				pack(newf->data, newf->len, "k", dhgenkey(netconn.dh.g, netconn.dh.sec, netconn.dh.p));
 				sendp(egress, newf);
 
 				if(debug)
 					fprint(2, "\tsent pubkey %ld\n", dhgenkey(netconn.dh.g, netconn.dh.sec, netconn.dh.p));
-	
+
 				break;
 			case NSdhx:
 				unpack(frame->data, frame->len, "k", &netconn.dh.pub);
 				netconn.state = NCSConnected;
 
 				if(debug)
-					fprint(2, "\trecvd pubkey %ld\n", netconn.dh.pub);
+					fprint(2, "\trcvd pubkey %ld\n", netconn.dh.pub);
 
 				netconn.dh.priv = dhgenkey(netconn.dh.pub, netconn.dh.sec, netconn.dh.p);
 				break;
 			}
 			break;
 		case NCSConnected:
+			if(verifyframe(frame, netconn.dh.priv) != 0){
+				if(debug)
+					fprint(2, "\tbad signature\n");
+				goto discard;
+			}
+
 			switch(frame->type){
 			case NSsimstate:
 				unpack(frame->data, frame->len, "PdPdP",
@@ -297,6 +305,7 @@ threadnetppu(void *)
 				break;
 			case NSnudge:
 				newf = newframe(frame, NCnudge, 0, 0, 0, nil);
+				signframe(newf, netconn.dh.priv);
 
 				sendp(egress, newf);
 
@@ -308,7 +317,7 @@ threadnetppu(void *)
 			break;
 		}
 discard:
-		free(frame);
+		delframe(frame);
 	}
 }
 
@@ -332,9 +341,8 @@ threadnetsend(void *arg)
 		if(debug){
 			rport = frame->udp.rport[0]<<8 | frame->udp.rport[1];
 			lport = frame->udp.lport[0]<<8 | frame->udp.lport[1];
-			fprint(2, "%I!%ud → %I!%ud | sent type %ud seq %ud ack %ud len %ud\n",
-				frame->udp.laddr, lport, frame->udp.raddr, rport,
-				frame->type, frame->seq, frame->ack, frame->len);
+			fprint(2, "%I!%ud → %I!%ud | sent %Φ\n",
+				frame->udp.laddr, lport, frame->udp.raddr, rport, frame);
 		}
 
 		free(frame);
@@ -438,6 +446,7 @@ threadmain(int argc, char *argv[])
 
 	GEOMfmtinstall();
 	fmtinstall('I', eipfmt);
+	fmtinstall(L'Φ', Φfmt);
 	ARGBEGIN{
 	case 'd':
 		debug++;
diff --git a/muswd.c b/muswd.c
index 9329545..d2f1f01 100644
--- a/muswd.c
+++ b/muswd.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <thread.h>
 #include <draw.h>
 #include <geometry.h>
@@ -46,7 +48,7 @@ popconn(NetConn *nc)
 
 	ncpe = conns+nconns;
 
-	for(ncp = conns; ncp < conns+nconns; ncp++)
+	for(ncp = conns; ncp < ncpe; ncp++)
 		if(*ncp == nc){
 			memmove(ncp, ncp+1, sizeof(NetConn*)*(ncpe-ncp-1));
 			nconns--;
@@ -77,9 +79,8 @@ threadnetrecv(void *arg)
 		if(debug){
 			rport = frame->udp.rport[0]<<8 | frame->udp.rport[1];
 			lport = frame->udp.lport[0]<<8 | frame->udp.lport[1];
-			fprint(2, "%I!%ud ← %I!%ud | rcvd type %ud seq %ud ack %ud len %ud\n",
-				frame->udp.laddr, lport, frame->udp.raddr, rport,
-				frame->type, frame->seq, frame->ack, frame->len);
+			fprint(2, "%I!%ud → %I!%ud | rcvd %Φ\n",
+				frame->udp.laddr, lport, frame->udp.raddr, rport, frame);
 		}
 	}
 	closeioproc(io);
@@ -103,13 +104,13 @@ threadnetppu(void *)
 			if(frame->type == NChi){
 				nc = newnetconn(NCSConnecting, &frame->udp);
 				putconn(nc);
-	
+
 				newf = newframe(frame, NShi, 0, 0, 2*sizeof(ulong), nil);
-	
+
 				dhgenpg(&nc->dh.p, &nc->dh.g);
 				pack(newf->data, newf->len, "kk", nc->dh.p, nc->dh.g);
 				sendp(egress, newf);
-	
+
 				if(debug)
 					fprint(2, "\tsent p %ld g %ld\n", nc->dh.p, nc->dh.g);
 			}else
@@ -124,10 +125,10 @@ threadnetppu(void *)
 				nc->state = NCSConnected;
 
 				if(debug)
-					fprint(2, "\trecvd pubkey %ld\n", nc->dh.pub);
+					fprint(2, "\trcvd pubkey %ld\n", nc->dh.pub);
 
 				newf = newframe(frame, NSdhx, 0, 0, sizeof(ulong), nil);
-	
+
 				nc->dh.sec = truerand();
 				nc->dh.priv = dhgenkey(nc->dh.pub, nc->dh.sec, nc->dh.p);
 				pack(newf->data, newf->len, "k", dhgenkey(nc->dh.g, nc->dh.sec, nc->dh.p));
@@ -140,6 +141,12 @@ threadnetppu(void *)
 			}
 			break;
 		case NCSConnected:
+			if(verifyframe(frame, nc->dh.priv) != 0){
+				if(debug)
+					fprint(2, "\tbad signature\n");
+				goto discard;
+			}
+
 			switch(frame->type){
 			case NCinput:
 				unpack(frame->data, frame->len, "k", &kdown);
@@ -150,13 +157,13 @@ threadnetppu(void *)
 				break;
 			case NCbuhbye:
 				popconn(nc);
-				free(nc);
+				delnetconn(nc);
 				break;
 			}
 			break;
 		}
 discard:
-		free(frame);
+		delframe(frame);
 	}
 }
 
@@ -180,9 +187,8 @@ threadnetsend(void *arg)
 		if(debug){
 			rport = frame->udp.rport[0]<<8 | frame->udp.rport[1];
 			lport = frame->udp.lport[0]<<8 | frame->udp.lport[1];
-			fprint(2, "%I!%ud → %I!%ud | sent type %ud seq %ud ack %ud len %ud\n",
-				frame->udp.laddr, lport, frame->udp.raddr, rport,
-				frame->type, frame->seq, frame->ack, frame->len);
+			fprint(2, "%I!%ud → %I!%ud | sent %Φ\n",
+				frame->udp.laddr, lport, frame->udp.raddr, rport, frame);
 		}
 
 		free(frame);
@@ -334,6 +340,7 @@ threadmain(int argc, char *argv[])
 
 	GEOMfmtinstall();
 	fmtinstall('I', eipfmt);
+	fmtinstall(L'Φ', Φfmt);
 	addr = "udp!*!112";
 	ARGBEGIN{
 	case 'a':
diff --git a/net.c b/net.c
index d645eb4..12c2c5b 100644
--- a/net.c
+++ b/net.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <thread.h>
 #include <draw.h>
 #include <geometry.h>
@@ -69,6 +71,7 @@ newframe(Frame *pf, u8int type, u32int seq, u32int ack, u16int len, uchar *data)
 	Frame *f;
 
 	f = emalloc(sizeof(Frame)+len);
+	memset(f, 0, sizeof(Frame));
 	f->id = ProtocolID;
 	f->type = type;
 	if(pf != nil){
@@ -87,6 +90,40 @@ newframe(Frame *pf, u8int type, u32int seq, u32int ack, u16int len, uchar *data)
 	return f;
 }
 
+void
+signframe(Frame *f, ulong key)
+{
+	uchar k[sizeof(ulong)];
+	uchar h[MD5dlen];
+	uchar msg[MTU];
+	int n;
+
+	k[0] = key; k[1] = key>>8; k[2] = key>>16; k[3] = key>>24;
+
+	memset(f->sig, 0, MD5dlen);
+	n = pack(msg, sizeof msg, "f", f);
+	hmac_md5(msg, n, k, sizeof k, h, nil);
+	memmove(f->sig, h, MD5dlen);
+}
+
+int
+verifyframe(Frame *f, ulong key)
+{
+	uchar k[sizeof(ulong)];
+	uchar h0[MD5dlen], h1[MD5dlen];
+	uchar msg[MTU];
+	int n;
+
+	k[0] = key; k[1] = key>>8; k[2] = key>>16; k[3] = key>>24;
+
+	memmove(h0, f->sig, MD5dlen);
+	memset(f->sig, 0, MD5dlen);
+	n = pack(msg, sizeof msg, "f", f);
+	hmac_md5(msg, n, k, sizeof k, h1, nil);
+	memmove(f->sig, h0, MD5dlen);
+	return memcmp(h0, h1, MD5dlen);
+}
+
 void
 delframe(Frame *f)
 {
diff --git a/pack.c b/pack.c
index 4680d73..f1a9a0a 100644
--- a/pack.c
+++ b/pack.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <draw.h>
 #include <geometry.h>
 #include "dat.h"
@@ -91,6 +93,7 @@ vpack(uchar *p, int n, char *fmt, va_list a)
 			put4(p, F->seq), p += 4;
 			put4(p, F->ack), p += 4;
 			put2(p, F->len), p += 2;
+			memmove(p, F->sig, MD5dlen), p += MD5dlen;
 
 			if(p+F->len > e)
 				goto err;
@@ -161,6 +164,7 @@ vunpack(uchar *p, int n, char *fmt, va_list a)
 			F->seq = get4(p), p += 4;
 			F->ack = get4(p), p += 4;
 			F->len = get2(p), p += 2;
+			memmove(F->sig, p, MD5dlen), p += MD5dlen;
 
 			if(p+F->len > e)
 				goto err;
diff --git a/party.c b/party.c
index ad3cd9b..6199b87 100644
--- a/party.c
+++ b/party.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <draw.h>
 #include <geometry.h>
 #include "dat.h"
diff --git a/physics.c b/physics.c
index 0fafea4..b588a4d 100644
--- a/physics.c
+++ b/physics.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <draw.h>
 #include <geometry.h>
 #include "dat.h"
diff --git a/sprite.c b/sprite.c
index aceceed..22dd00b 100644
--- a/sprite.c
+++ b/sprite.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <draw.h>
 #include <geometry.h>
 #include "dat.h"
diff --git a/universe.c b/universe.c
index 7a17b56..eea95a8 100644
--- a/universe.c
+++ b/universe.c
@@ -1,6 +1,8 @@
 #include <u.h>
 #include <libc.h>
 #include <ip.h>
+#include <mp.h>
+#include <libsec.h>
 #include <draw.h>
 #include <geometry.h>
 #include "dat.h"
-- 
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