Index: usr.sbin/bhyve/pci_e82545.c
===================================================================
--- usr.sbin/bhyve/pci_e82545.c
+++ usr.sbin/bhyve/pci_e82545.c
@@ -233,7 +233,7 @@
  * Debug printf
  */
 static int e82545_debug = 0;
-#define WPRINTF(msg,params...) PRINTLN("e82545: " msg, params)
+#define WPRINTF(msg,params...) PRINTLN("e82545: " msg, ##params)
 #define DPRINTF(msg,params...) if (e82545_debug) WPRINTF(msg, params)
 
 #define	MIN(a,b) (((a)<(b))?(a):(b))
@@ -1086,15 +1086,18 @@
 	union  e1000_tx_udesc *dsc;
 	int desc, dtype, len, ntype, iovcnt, tcp, tso;
 	int mss, paylen, seg, tiovcnt, left, now, nleft, nnow, pv, pvoff;
-	unsigned hdrlen, vlen;
+	unsigned hdrlen, vlen, pktlen;
 	uint32_t tcpsum, tcpseq;
 	uint16_t ipcs, tcpcs, ipid, ohead;
+	bool invalid;
 
 	ckinfo[0].ck_valid = ckinfo[1].ck_valid = 0;
 	iovcnt = 0;
 	ntype = 0;
 	tso = 0;
+	pktlen = 0;
 	ohead = head;
+	invalid = false;
 
 	/* iovb[0/1] may be used for writable copy of headers. */
 	iov = &iovb[2];
@@ -1144,17 +1147,23 @@
 		len = (dtype == E1000_TXD_TYP_L) ? dsc->td.lower.flags.length :
 		    dsc->dd.lower.data & 0xFFFFF;
 
-		if (len > 0) {
-			/* Strip checksum supplied by guest. */
-			if ((dsc->td.lower.data & E1000_TXD_CMD_EOP) != 0 &&
-			    (dsc->td.lower.data & E1000_TXD_CMD_IFCS) == 0)
+		/* Strip checksum supplied by guest. */
+		if ((dsc->td.lower.data & E1000_TXD_CMD_EOP) != 0 &&
+		    (dsc->td.lower.data & E1000_TXD_CMD_IFCS) == 0) {
+			if (len <= 2) {
+				WPRINTF("final descriptor too short (%d) -- dropped",
+				    len);
+				invalid = true;
+			} else
 				len -= 2;
-			if (iovcnt < I82545_MAX_TXSEGS) {
-				iov[iovcnt].iov_base = paddr_guest2host(
-				    sc->esc_ctx, dsc->td.buffer_addr, len);
-				iov[iovcnt].iov_len = len;
-			}
+		}
+
+		if (len > 0 && iovcnt < I82545_MAX_TXSEGS) {
+			iov[iovcnt].iov_base = paddr_guest2host(sc->esc_ctx,
+			    dsc->td.buffer_addr, len);
+			iov[iovcnt].iov_len = len;
 			iovcnt++;
+			pktlen += len;
 		}
 
 		/*
@@ -1202,6 +1211,9 @@
 		}
 	}
 
+	if (invalid)
+		goto done;
+
 	if (iovcnt > I82545_MAX_TXSEGS) {
 		WPRINTF("tx too many descriptors (%d > %d) -- dropped",
 		    iovcnt, I82545_MAX_TXSEGS);
@@ -1295,8 +1307,13 @@
 		}
 	}
 
+	if (pktlen < hdrlen + vlen) {
+		WPRINTF("packet too small for writable header");
+		goto done;
+	}
+
 	/* Allocate, fill and prepend writable header vector. */
-	if (hdrlen != 0) {
+	if (hdrlen + vlen != 0) {
 		hdr = __builtin_alloca(hdrlen + vlen);
 		hdr += vlen;
 		for (left = hdrlen, hdrp = hdr; left > 0;