omudpspoof: add support for packets larger than 1472 bytes

On Ethernet, they need to be transmitted in multiple fragments. While
it is known that fragmentation can cause issues, it is the best choice
to be made in that case. Also improved debug output.

1 files changed, 82 insertions, 15 deletions

diff --git a/plugins/omudpspoof/omudpspoof.c b/plugins/omudpspoof/omudpspoof.c
index c692acfb..c34e508e 100644
--- a/plugins/omudpspoof/omudpspoof.c
+++ b/plugins/omudpspoof/omudpspoof.c
@@ -316,6 +316,7 @@ CODESTARTdbgPrintInstInfo
 ENDdbgPrintInstInfo
 
 
+#define MTU 1500 /* min max MTU we support - 1500 for ethernet TODO: config option? */
 /* Send a message via UDP
  * Note: libnet is not thread-safe, so we need to ensure that only one
  * instance ever is calling libnet code.
@@ -331,12 +332,22 @@ UDPSend(instanceData *pData, uchar *pszSourcename, char *msg, size_t len)
 	libnet_ptag_t ip, ipo;
 	libnet_ptag_t udp;
 	sbool bNeedUnlock = 0;
+	/* hdrOffs = fragmentation flags + offset (in bytes)
+	* divided by 8 */
+	unsigned msgOffs, hdrOffs; 
+	unsigned maxPktLen, pktLen;
 	DEFiRet;
 
 	if(pData->pSockArray == NULL) {
 		CHKiRet(doTryResume(pData));
 	}
 
+	if(len > 65528) {
+		DBGPRINTF("omudpspoof: msg with length %d truncated to 64k: '%.768s'\n",
+			  len, msg);
+		len = 65528;
+	}
+
 	ip = ipo = udp = 0;
 	if(pData->sourcePort++ >= pData->sourcePortEnd){
 		pData->sourcePort = pData->sourcePortStart;
@@ -349,15 +360,30 @@ UDPSend(instanceData *pData, uchar *pszSourcename, char *msg, size_t len)
 	bNeedUnlock = 1;
 	for (r = pData->f_addr; r && bSendSuccess == RSFALSE ; r = r->ai_next) {
 		tempaddr = (struct sockaddr_in *)r->ai_addr;
+		/* Getting max payload size (must be multiple of 8) */
+		maxPktLen = (MTU - LIBNET_IPV4_H) & ~0x07;
+		msgOffs = 0;
+		/* We're doing (payload size - UDP header size) and not
+		* checking if it's a multiple of 8 because we know the
+		* header is 8 bytes long */
+		if(len > (maxPktLen - LIBNET_UDP_H) ) {
+			hdrOffs = IP_MF;
+			pktLen = maxPktLen - LIBNET_UDP_H;
+		} else {
+			hdrOffs = 0;
+			pktLen = len;
+		}
+		DBGPRINTF("omudpspoof: stage 1: MF:%d, hdrOffs %d, pktLen %d\n",
+			  (hdrOffs & IP_MF) >> 13, (hdrOffs & 0x1FFF) << 3, pktLen);
 		libnet_clear_packet(libnet_handle);
 		/* note: libnet does need ports in host order NOT in network byte order! -- rgerhards, 2009-11-12 */
 		udp = libnet_build_udp(
 			ntohs(pData->sourcePort),/* source port */
 			ntohs(tempaddr->sin_port),/* destination port */
-			LIBNET_UDP_H + len,	/* packet length */
+			pktLen+LIBNET_UDP_H,	/* packet length */
 			0,			/* checksum */
 			(u_char*)msg,		/* payload */
-			len,			/* payload size */
+			pktLen,	                /* payload size */
 			libnet_handle,		/* libnet handle */
 			udp);			/* libnet id */
 		if (udp == -1) {
@@ -365,10 +391,10 @@ UDPSend(instanceData *pData, uchar *pszSourcename, char *msg, size_t len)
 		}
 
 		ip = libnet_build_ipv4(
-			LIBNET_IPV4_H +  len + LIBNET_UDP_H, /* length */
+			LIBNET_IPV4_H+LIBNET_UDP_H+pktLen, /* length */
 			0,				/* TOS */
 			242,				/* IP ID */
-			0,				/* IP Frag */
+			hdrOffs,			/* IP Frag */
 			64,				/* TTL */
 			IPPROTO_UDP,			/* protocol */
 			0,				/* checksum */
@@ -384,20 +410,62 @@ UDPSend(instanceData *pData, uchar *pszSourcename, char *msg, size_t len)
 
 		/* Write it to the wire. */
 		lsent = libnet_write(libnet_handle);
-		if(lsent != LIBNET_IPV4_H+LIBNET_UDP_H+len) {
-			DBGPRINTF("omudpspoof: write error len %d, sent %d: %s\n",
-				  LIBNET_IPV4_H+LIBNET_UDP_H+len, lsent, libnet_geterror(libnet_handle));
+		if(lsent != (int) (LIBNET_IPV4_H+LIBNET_UDP_H+pktLen)) {
+			DBGPRINTF("omudpspoof: write error (total len %d): pktLen %d, sent %d: %s\n",
+				  len, LIBNET_IPV4_H+LIBNET_UDP_H+pktLen, lsent, libnet_geterror(libnet_handle));
 			if(lsent != -1) {
 				bSendSuccess = RSTRUE;
 			}
 		} else {
 			bSendSuccess = RSTRUE;
 		}
-	}
-	/* finished looping */
-	if(bSendSuccess == RSFALSE) {
-		DBGPRINTF("omudpspoof: error sending message, suspending\n");
-		iRet = RS_RET_SUSPENDED;
+		msgOffs += pktLen;
+
+		/* We need to get rid of the UDP header to build the other fragments */
+		libnet_clear_packet(libnet_handle);
+		ip = LIBNET_PTAG_INITIALIZER;
+		while(len > msgOffs ) { /* loop until all payload is sent */
+			/* check if there will be more fragments */
+			if((len - msgOffs) > maxPktLen) {
+				/* In IP's eyes, the UDP header in the first packet
+				* needs to be in the offset, so we add its size to
+				* the payload offset here */
+				hdrOffs = IP_MF + (msgOffs + LIBNET_UDP_H)/8;
+				pktLen = maxPktLen;
+			} else {
+				/* See above */
+				hdrOffs = (msgOffs + LIBNET_UDP_H)/8;
+				pktLen = len - msgOffs;
+			}
+			DBGPRINTF("omudpspoof: stage 2: MF:%d, hdrOffs %d, pktLen %d\n",
+				  (hdrOffs & IP_MF) >> 13, (hdrOffs & 0x1FFF) << 3, pktLen);
+			ip = libnet_build_ipv4(
+				LIBNET_IPV4_H + pktLen,         /* length */
+				0,				/* TOS */
+				242,				/* IP ID */
+				hdrOffs,			/* IP Frag */
+				64,				/* TTL */
+				IPPROTO_UDP,			/* protocol */
+				0,				/* checksum */
+				source_ip.sin_addr.s_addr,
+				tempaddr->sin_addr.s_addr,
+				(u_int8_t*)(msg+msgOffs),	/* payload */
+				pktLen,		/* payload size */
+				libnet_handle,			/* libnet handle */
+				ip);				/* libnet id */
+			if (ip == -1) {
+				DBGPRINTF("omudpspoof: can't build IP fragment header: %s\n", libnet_geterror(libnet_handle));
+			}
+			/* Write it to the wire. */
+			lsent = libnet_write(libnet_handle);
+			if(lsent != (int) (LIBNET_IPV4_H+pktLen)) {
+				DBGPRINTF("omudpspoof: fragment write error len %d, sent %d: %s\n",
+					  LIBNET_IPV4_H+LIBNET_UDP_H+len, lsent, libnet_geterror(libnet_handle));
+				bSendSuccess = RSFALSE;
+				continue;
+			}
+			msgOffs += pktLen;
+		}
 	}
 
 finalize_it:
@@ -422,7 +490,7 @@ static rsRetVal doTryResume(instanceData *pData)
 		FINALIZE;
 
 	/* The remote address is not yet known and needs to be obtained */
-	DBGPRINTF(" %s\n", pData->host);
+	DBGPRINTF("omudpspoof trying resume for '%s'\n", pData->host);
 	memset(&hints, 0, sizeof(hints));
 	/* port must be numeric, because config file syntax requires this */
 	hints.ai_flags = AI_NUMERICSERV;
@@ -464,8 +532,7 @@ CODESTARTdoAction
 
 	iMaxLine = glbl.GetMaxLine();
 
-	//TODO: enable THIS one! DBGPRINTF(" %s:%s/omudpspoof, src '%s', msg strt '%.256s'\n", pData->host,
-	DBGPRINTF(" %s:%s/omudpspoof, src '%s', msg strt '%s'\n", pData->host,
+	DBGPRINTF(" %s:%s/omudpspoof, src '%s', msg strt '%.256s'\n", pData->host,
 		  getFwdPt(pData), ppString[1], ppString[0]);
 
 	psz = (char*) ppString[0];