Index: bpf.c
===================================================================
RCS file: /cvs/src/usr.sbin/dhcrelay/bpf.c,v
retrieving revision 1.19
diff -u -p -r1.19 bpf.c
--- bpf.c	19 Apr 2017 05:36:12 -0000	1.19
+++ bpf.c	24 Nov 2017 02:10:48 -0000
@@ -375,6 +375,7 @@ receive_packet(struct interface_info *in
 	int length = 0;
 	ssize_t offset = 0;
 	struct bpf_hdr hdr;
+	size_t bpflen, pktoff;
 
 	/*
 	 * All this complexity is because BPF doesn't guarantee that
@@ -412,12 +413,14 @@ receive_packet(struct interface_info *in
 		memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
 		    sizeof(hdr));
 
+		bpflen = BPF_WORDALIGN(hdr.bh_hdrlen + hdr.bh_caplen);
+		pktoff = interface->rbuf_offset + hdr.bh_hdrlen;
+
 		/*
 		 * If the bpf header plus data doesn't fit in what's
 		 * left of the buffer, stick head in sand yet again...
 		 */
-		if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
-		    interface->rbuf_len) {
+		if (interface->rbuf_offset + bpflen > interface->rbuf_len) {
 			interface->rbuf_offset = interface->rbuf_len;
 			continue;
 		}
@@ -427,18 +430,14 @@ receive_packet(struct interface_info *in
 		 * the packet won't fit in the input buffer, all we can
 		 * do is drop it.
 		 */
-		if (hdr.bh_caplen != hdr.bh_datalen) {
-			interface->rbuf_offset += hdr.bh_hdrlen =
-			    hdr.bh_caplen;
+		if (hdr.bh_caplen < hdr.bh_datalen) {
+			interface->rbuf_offset += bpflen;
 			continue;
 		}
 
-		/* Skip over the BPF header... */
-		interface->rbuf_offset += hdr.bh_hdrlen;
-
 		/* Decode the physical header... */
 		offset = decode_hw_header(interface->rbuf,
-		    interface->rbuf_len, interface->rbuf_offset, pc,
+		    interface->rbuf_len, pktoff, pc,
 		    interface->hw_address.htype);
 
 		/*
@@ -447,7 +446,7 @@ receive_packet(struct interface_info *in
 		 * skip this packet.
 		 */
 		if (offset < 0) {
-			interface->rbuf_offset += hdr.bh_caplen;
+			interface->rbuf_offset += bpflen;
 			continue;
 		}
 
@@ -457,27 +456,23 @@ receive_packet(struct interface_info *in
 
 		/* If the IP or UDP checksum was bad, skip the packet... */
 		if (offset < 0) {
-			interface->rbuf_offset += hdr.bh_caplen;
+			interface->rbuf_offset += bpflen;
 			continue;
 		}
 
-		hdr.bh_caplen -= offset - interface->rbuf_offset;
-		interface->rbuf_offset = offset;
-
 		/*
 		 * If there's not enough room to stash the packet data,
 		 * we have to skip it (this shouldn't happen in real
 		 * life, though).
 		 */
 		if (hdr.bh_caplen > len) {
-			interface->rbuf_offset += hdr.bh_caplen;
+			interface->rbuf_offset += bpflen;
 			continue;
 		}
 
 		/* Copy out the data in the packet... */
-		memcpy(buf, interface->rbuf + interface->rbuf_offset,
-		    hdr.bh_caplen);
-		interface->rbuf_offset += hdr.bh_caplen;
+		memcpy(buf, interface->rbuf + pktoff, hdr.bh_caplen);
+		interface->rbuf_offset += bpflen;
 		return (hdr.bh_caplen);
 	} while (!length);
 	return (0);