src/whsniff.c: add -k option to keep original FCS

Allow the user to keep the original FCS sent by the CC2531 which contains the RSSI and LQI. These values can be interpreted by wireshark as a "TI CC24xx FCS format" Reason: Add -k option to keep original FCS Author: Fabrice Fontaine Ref: 698285 License: same as original file 698285 by Fabrice Fontaine: Patch for whsniff (Zigbee sniffer) Signed-off-by: Fabrice Fontaine <[email protected]>
homewsn · Nov 6, 2020 · dfc3c3d · dfc3c3d
1 parent 76bb8cb
commit dfc3c3d
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Showing 2 changed files with 26 additions and 13 deletions.
diff --git a/ReadMe.md b/ReadMe.md
@@ -72,6 +72,10 @@ $ path/to/whsniff -c channel_number > /tmp/pipes/whsniff
 ```sh
 $ path/to/whsniff -c channel_number > filename.pcap
 ```
+* You can also keep the original FCS sent by the CC2531 through the -k option. The original FCS contains the RSSI and LQI. It can be interpreted by wireshark as a "TI CC24xx FCS format":
+```sh
+$ path/to/whsniff -k -c channel_number > /tmp/pipes/whsniff
+```
 * If you see something like `libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/001/006: Permission denied` you can use `udev`
 
     1. Add below contents to `/etc/udev/rules.d/54-cc2531.rules`

diff --git a/src/whsniff.c b/src/whsniff.c
@@ -100,7 +100,7 @@ static uint16_t ieee802154_crc16(uint8_t *tvb, uint32_t offset, uint32_t len);
 
 
 //--------------------------------------------
-static int packet_handler(unsigned char *buf, int cnt)
+static int packet_handler(unsigned char *buf, int cnt, uint8_t keep_original_fcs)
 {
 	usb_header_type *usb_header;
 	usb_data_header_type *usb_data_header;
@@ -162,7 +162,6 @@ static int packet_handler(unsigned char *buf, int cnt)
 			pcaprec_hdr.orig_len = (uint32_t)usb_data_header->wpan_len;
 
 			fwrite(&pcaprec_hdr, sizeof(pcaprec_hdr), 1, stdout);
-			fwrite(&buf[sizeof(usb_data_header_type)], 1, usb_data_header->wpan_len - 2, stdout);
 
 			// SmartRF™ Packet Sniffer User’s Manual (SWRU187G)
 			// FCS:
@@ -172,15 +171,21 @@ static int packet_handler(unsigned char *buf, int cnt)
 			// Bit 6-0: If Correlation used: Correlation value.
 			// If Correlation not used: LQI.
 
-			fcs = 0;
-			if (buf[sizeof(usb_data_header_type) + usb_data_header->wpan_len - 1] & 0x80)
+			if (keep_original_fcs)
+				fwrite(&buf[sizeof(usb_data_header_type)], 1, usb_data_header->wpan_len, stdout);
+			else
 			{
-				// CRC OK
-				fcs = ieee802154_crc16((uint8_t *)&buf[sizeof(usb_data_header_type)], 0, usb_data_header->wpan_len - 2);
-			}
-			le_fcs = htole16(fcs);
+				fwrite(&buf[sizeof(usb_data_header_type)], 1, usb_data_header->wpan_len - 2, stdout);
+				fcs = 0;
+				if (buf[sizeof(usb_data_header_type) + usb_data_header->wpan_len - 1] & 0x80)
+				{
+					// CRC OK
+					fcs = ieee802154_crc16((uint8_t *)&buf[sizeof(usb_data_header_type)], 0, usb_data_header->wpan_len - 2);
+				}
+				le_fcs = htole16(fcs);
 
-			fwrite(&le_fcs, sizeof(le_fcs), 1, stdout);
+				fwrite(&le_fcs, sizeof(le_fcs), 1, stdout);
+			}
 			fflush(stdout);
 
 			break;
@@ -209,7 +214,7 @@ void signal_handler(int sig)
 //--------------------------------------------
 void print_usage()
 {
-    printf("Usage: whsniff -c channel\n");
+    printf("Usage: whsniff -c channel [-k]\n");
 }
 
 //--------------------------------------------
@@ -219,6 +224,7 @@ int main(int argc, char *argv[])
 	libusb_device_handle *handle;
 	libusb_device *dev;
 	uint8_t channel;
+	uint8_t keep_original_fcs = 0;
 	int option;
 	static unsigned char usb_buf[BUF_SIZE];
 	static int usb_cnt;
@@ -232,14 +238,14 @@ int main(int argc, char *argv[])
 	// pipe closed
 	signal(SIGPIPE, signal_handler);
 
-	if (argc != 3)
+	if (argc != 3 && argc != 4)
 	{
 		print_usage();
 		exit(EXIT_FAILURE);
 	}
 
 	option = 0;
-	while ((option = getopt(argc, argv, "c:")) != -1)
+	while ((option = getopt(argc, argv, "c:k")) != -1)
 	{
 		switch (option)
 		{
@@ -251,6 +257,9 @@ int main(int argc, char *argv[])
 					exit(EXIT_FAILURE);
 				}
 				break;
+			case 'k':
+				keep_original_fcs = 1;
+				break;
 			default:
 				print_usage();
 				exit(EXIT_FAILURE);
@@ -379,7 +388,7 @@ int main(int argc, char *argv[])
 
 		for (;;)
 		{
-			res = packet_handler(&recv_buf[0], recv_cnt);
+			res = packet_handler(&recv_buf[0], recv_cnt, keep_original_fcs);
 			if (res < 0)
 				break;
 			recv_cnt -= res;