stun

commit eec19fac6675df594355c653abf331a6b17c8057
parent 777ef1489c602ac28cc6a068b2a7a48f77126ce1
Author: sin <sin@2f30.org>
Date:   Tue, 29 Mar 2016 10:11:13 +0100

frail attempt at handling "bad packets"

Diffstat:
M
stun.c
 | 
49
+++++++++++++++++++++++++++++++++++++++++--------

1 file changed, 41 insertions(+), 8 deletions(-)
diff --git a/stun.c b/stun.c
@@ -46,6 +46,8 @@
 #define CHALLENGETIMEO	1  /* in seconds */
 #define RECONNECTTIMEO	60 /* in seconds */
 #define HDRLEN		2
+#define PKTLENMASK	0xfff
+#define BADPKT		0x8000
 #define MTU		1440
 
 enum {
@@ -115,7 +117,7 @@ logerr(char *msg, ...)
 int
 padto(int len, int blocksize)
 {
-	return len + blocksize - (len & (blocksize - 1));
+	return len + blocksize - len % blocksize;
 }
 
 int
@@ -410,19 +412,36 @@ readnet(int fd, unsigned char *buf, int len)
 	unsigned char hdr[HDRLEN];
 	int n, pktlen, paddedlen;
 
+	/* read unpadded packet length */
 	n = readall(fd, hdr, sizeof(hdr));
 	if (n <= 0)
 		return n;
+
 	pktlen = unpack16(hdr);
+	pktlen &= PKTLENMASK;
 	paddedlen = padto(pktlen, AES_BLOCK_SIZE);
+
+	/* attempt to drain an invalid packet */
 	if (pktlen < 0 || pktlen > len ||
 	    paddedlen < 0 || paddedlen > MTU + AES_BLOCK_SIZE) {
-		logwarn("bogus payload length: %d", paddedlen);
-		return -1;
+		while (paddedlen) {
+			if (paddedlen > MTU + AES_BLOCK_SIZE)
+				len = MTU + AES_BLOCK_SIZE;
+			else
+				len = paddedlen;
+			n = readall(fd, encbuf, len);
+			if (n <= 0)
+				break;
+			paddedlen -= n;
+		}
+		return BADPKT;
 	}
+
+	/* read encrypted payload */
 	n = readall(fd, encbuf, paddedlen);
 	if (n <= 0)
 		return n;
+
 	aesdec(&dec, decbuf, encbuf, paddedlen);
 	memcpy(buf, decbuf, pktlen);
 	return pktlen;
@@ -468,7 +487,8 @@ challenge(int netfd)
 		goto err;
 	default:
 		if (pfd[0].revents & (POLLIN | POLLHUP)) {
-			if (readnet(netfd, buf, sizeof(buf)) <= 0)
+			ret = readnet(netfd, buf, sizeof(buf));
+			if (ret <= 0 || ret == BADPKT)
 				goto err;
 			reply = unpack32(buf);
 			if (n + 1 == reply) {
@@ -487,8 +507,10 @@ response(int netfd)
 {
 	unsigned char buf[sizeof(uint32_t)];
 	uint32_t reply;
+	int ret;
 
-	if (readnet(netfd, buf, sizeof(buf)) <= 0)
+	ret = readnet(netfd, buf, sizeof(buf));
+	if (ret <= 0 || ret == BADPKT)
 		return -1;
 	reply = unpack32(buf);
 	pack32(buf, reply + 1);
@@ -512,13 +534,24 @@ tunnel(int netfd, int devfd)
 		ret = poll(pfd, 2, -1);
 		if (ret < 0)
 			logerr("poll failed");
+
 		if (pfd[0].revents & (POLLERR | POLLNVAL) ||
 		    pfd[1].revents & (POLLERR | POLLNVAL))
 			logerr("bad fd in poll set");
-		if (pfd[0].revents & (POLLIN | POLLHUP))
-			if ((n = readnet(netfd, buf, MTU)) <= 0 ||
-			    (n = writedev(devfd, buf, n)) <= 0)
+
+		if (pfd[0].revents & (POLLIN | POLLHUP)) {
+			n = readnet(netfd, buf, MTU);
+			if (n <= 0)
 				return 1;
+			if (n == BADPKT) {
+				logwarn("bad packet");
+			} else {
+				n = writedev(devfd, buf, n);
+				if (n <= 0)
+					return 1;
+			}
+		}
+
 		if (pfd[1].revents & (POLLIN | POLLHUP))
 			if ((n = readdev(devfd, buf, MTU)) <= 0 ||
 			    (n = writenet(netfd, buf, n)) <= 0)