Only add VLAN tags for Ethernet.

The code to insert VLAN tags was assuming Ethernet packets; that's not
the case, for example, if you're capturing on the "any" device, as the
packet headers aren't Ethernet headers.  Have a flag in the pcap
structure to indicate whether to check for and add VLAN tags, and set it
only if we're using PF_PACKET sockets, we're getting Ethernet headers,
and, if we're using the memory-mapped capture mechanism, it's not
version 1.

This should fix SourceForge bug 3525828.

pcap-int.h

@@ -144,6 +144,7 @@ struct pcap_md {
 	char	*mondevice;	/* mac80211 monitor device we created */
 	u_char	*mmapbuf;	/* memory-mapped region pointer */
 	size_t	mmapbuflen;	/* size of region */
+	int	add_vlan_tags;	/* 1 if we should insert VLAN tags */
 	u_int	tp_version;	/* version of tpacket_hdr for mmaped ring */
 	u_int	tp_hdrlen;	/* hdrlen of tpacket_hdr for mmaped ring */
 	u_char	*oneshot_buffer; /* buffer for copy of packet */

pcap-linux.c

@@ -1530,32 +1530,34 @@ pcap_read_packet(pcap_t *handle, pcap_handler callback, u_char *userdata)
 	}
 
 #if defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI)
-	for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
-		struct tpacket_auxdata *aux;
-		unsigned int len;
-		struct vlan_tag *tag;
-
-		if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct tpacket_auxdata)) ||
-		    cmsg->cmsg_level != SOL_PACKET ||
-		    cmsg->cmsg_type != PACKET_AUXDATA)
-			continue;
+	if (handle->md.add_vlan_tags) {
+		for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+			struct tpacket_auxdata *aux;
+			unsigned int len;
+			struct vlan_tag *tag;
 
-		aux = (struct tpacket_auxdata *)CMSG_DATA(cmsg);
-		if (aux->tp_vlan_tci == 0)
-			continue;
+			if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct tpacket_auxdata)) ||
+			    cmsg->cmsg_level != SOL_PACKET ||
+			    cmsg->cmsg_type != PACKET_AUXDATA)
+				continue;
 
-		len = packet_len > iov.iov_len ? iov.iov_len : packet_len;
-		if (len < 2 * ETH_ALEN)
-			break;
+			aux = (struct tpacket_auxdata *)CMSG_DATA(cmsg);
+			if (aux->tp_vlan_tci == 0)
+				continue;
 
-		bp -= VLAN_TAG_LEN;
-		memmove(bp, bp + VLAN_TAG_LEN, 2 * ETH_ALEN);
+			len = packet_len > iov.iov_len ? iov.iov_len : packet_len;
+			if (len < 2 * ETH_ALEN)
+				break;
+
+			bp -= VLAN_TAG_LEN;
+			memmove(bp, bp + VLAN_TAG_LEN, 2 * ETH_ALEN);
 
-		tag = (struct vlan_tag *)(bp + 2 * ETH_ALEN);
-		tag->vlan_tpid = htons(ETH_P_8021Q);
-		tag->vlan_tci = htons(aux->tp_vlan_tci);
+			tag = (struct vlan_tag *)(bp + 2 * ETH_ALEN);
+			tag->vlan_tpid = htons(ETH_P_8021Q);
+			tag->vlan_tci = htons(aux->tp_vlan_tci);
 
-		packet_len += VLAN_TAG_LEN;
+			packet_len += VLAN_TAG_LEN;
+		}
 	}
 #endif /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */
 #endif /* HAVE_PF_PACKET_SOCKETS */
@@ -3043,6 +3045,19 @@ activate_new(pcap_t *handle)
 	}
 	handle->bufsize = handle->snapshot;
 
+	/*
+	 * Only enable the insertion of VLAN tags if the link-layer
+	 * header type is Ethernet.  If it should be supported on
+	 * any other link-layer type, the code that inserts them
+	 * must be modified to insert them in the proper place, which
+	 * differs from link-layer header type to link-layer header
+	 * type.
+	 */
+	if (handle->linktype == DLT_EN10MB)
+		handle->md.add_vlan_tags = 1;
+	else
+		handle->md.add_vlan_tags = 0;
+
 	/* Save the socket FD in the pcap structure */
 	handle->fd = sock_fd;
 
@@ -3130,6 +3145,14 @@ activate_mmap(pcap_t *handle, int *status)
 	handle->getnonblock_op = pcap_getnonblock_mmap;
 	handle->oneshot_callback = pcap_oneshot_mmap;
 	handle->selectable_fd = handle->fd;
+
+	/*
+	 * We only support inserting VLAN tags for tpacket V2;
+	 * if we're using v1, disable it.
+	 */
+	if (handle->md.tp_version == TPACKET_V1)
+		handle->md.add_vlan_tags = 0;
+
 	return 1;
 }
 #else /* HAVE_PACKET_RING */
@@ -3882,7 +3905,7 @@ pcap_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler callback,
 		}
 
 #ifdef HAVE_TPACKET2
-		if (handle->md.tp_version == TPACKET_V2 && h.h2->tp_vlan_tci &&
+		if (handle->md.add_vlan_tags && h.h2->tp_vlan_tci &&
 		    tp_snaplen >= 2 * ETH_ALEN) {
 			struct vlan_tag *tag;
 
@@ -5075,6 +5098,11 @@ activate_old(pcap_t *handle)
 	 */
 	handle->offset	 = 0;
 
+	/*
+	 * No support for getting VLAN tags to insert.
+	 */
+	handle->md.add_vlan_tags = 0;
+
 	return 1;
 }