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authorGuy Harris <guy@alum.mit.edu>2018-04-14 18:46:29 -0700
committerGuy Harris <guy@alum.mit.edu>2018-04-15 01:47:18 +0000
commite4d3916530aed332fcb39d4017e633bd51c4277c (patch)
tree960bf82e271dbd908368693fd144f34a9d038d40
parent4994955600fae29cc69eaf638fed695e82d47146 (diff)
Clean up the way we handle the FCS.
For the "802.15.4 with FCS" link-layer type, strip what FCS we find, if any, off and use that new tvbuff for all dissection except for checking and dissection of the FCS itself. For the "802.15.4 without FCS" link-layer type, don't fake an uncaptured FCS by increasing the reported length, just use the tvbuff as is. This means we handle 802.15.4 the same way we handle other link-layer types where the FCS might, or might not, appear as part of the captured data. Change-Id: Ia91b7fb0aad495876be00bf813c6b6517e5e11d7 Reviewed-on: https://code.wireshark.org/review/26947 Reviewed-by: Guy Harris <guy@alum.mit.edu>
-rw-r--r--epan/dissectors/packet-ieee802154.c136
1 files changed, 100 insertions, 36 deletions
diff --git a/epan/dissectors/packet-ieee802154.c b/epan/dissectors/packet-ieee802154.c
index 7e7c9ab..90cd21c 100644
--- a/epan/dissectors/packet-ieee802154.c
+++ b/epan/dissectors/packet-ieee802154.c
@@ -73,9 +73,10 @@ void proto_register_ieee802154(void);
void proto_reg_handoff_ieee802154(void);
/* Dissection Options for dissect_ieee802154_common */
-#define DISSECT_IEEE802154_OPTION_CC24xx 0x00000001 /* FCS field contains a TI CC24xx style FCS. */
-#define DISSECT_IEEE802154_OPTION_LINUX 0x00000002 /* Addressing fields are padded DLT_IEEE802_15_4_LINUX, not implemented. */
-#define DISSECT_IEEE802154_OPTION_ZBOSS 0x00000004 /* ZBOSS traffic dump */
+#define DISSECT_IEEE802154_OPTION_FCS_PRESENT 0x00000001 /* FCS field present */
+#define DISSECT_IEEE802154_OPTION_CC24xx 0x00000002 /* FCS field contains a TI CC24xx style FCS. */
+#define DISSECT_IEEE802154_OPTION_LINUX 0x00000004 /* Addressing fields are padded DLT_IEEE802_15_4_LINUX, not implemented. */
+#define DISSECT_IEEE802154_OPTION_ZBOSS 0x00000008 /* ZBOSS traffic dump */
/* ethertype for 802.15.4 tag - encapsulating an Ethernet packet */
static unsigned int ieee802154_ethertype = 0x809A;
@@ -1207,16 +1208,16 @@ static int
dissect_ieee802154(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
tvbuff_t *new_tvb = dissect_zboss_specific(tvb, pinfo, tree);
- guint options = 0;
+ guint options = DISSECT_IEEE802154_OPTION_FCS_PRESENT;
if (ieee802154_cc24xx)
{
- options = DISSECT_IEEE802154_OPTION_CC24xx;
+ options |= DISSECT_IEEE802154_OPTION_CC24xx;
}
if (new_tvb != tvb)
{
/* ZBOSS traffic dump: always TI FCS, always ZigBee */
- options = (DISSECT_IEEE802154_OPTION_CC24xx | DISSECT_IEEE802154_OPTION_ZBOSS);
+ options |= (DISSECT_IEEE802154_OPTION_CC24xx | DISSECT_IEEE802154_OPTION_ZBOSS);
}
/* Call the common dissector. */
dissect_ieee802154_common(new_tvb, pinfo, tree, options);
@@ -1234,19 +1235,8 @@ dissect_ieee802154(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* da
static int
dissect_ieee802154_nofcs(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void * data _U_)
{
- tvbuff_t *new_tvb;
- /* If there is no FCS present in the reported packet, then the length of
- * the true IEEE 802.15.4 packet is actually 2 bytes longer. Re-create
- * the buffer with an extended reported length so that the packet will
- * be handled as though the FCS were truncated.
- *
- * Note, we can't just call tvb_set_reported_length(), because it includes
- * checks to ensure that the new reported length is not longer than the old
- * reported length (why?), and will throw an exception.
- */
- new_tvb = tvb_new_subset_length_caplen(tvb, 0, -1, tvb_reported_length(tvb)+IEEE802154_FCS_LEN);
/* Call the common dissector. */
- dissect_ieee802154_common(new_tvb, pinfo, tree, 0);
+ dissect_ieee802154_common(tvb, pinfo, tree, 0);
return tvb_captured_length(tvb);
} /* dissect_ieee802154_nofcs */
@@ -1311,7 +1301,7 @@ static int
dissect_ieee802154_cc24xx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void * data _U_)
{
/* Call the common dissector. */
- dissect_ieee802154_common(tvb, pinfo, tree, DISSECT_IEEE802154_OPTION_CC24xx);
+ dissect_ieee802154_common(tvb, pinfo, tree, DISSECT_IEEE802154_OPTION_FCS_PRESENT|DISSECT_IEEE802154_OPTION_CC24xx);
return tvb_captured_length(tvb);
} /* dissect_ieee802154_cc24xx */
@@ -1323,7 +1313,7 @@ dissect_ieee802154_cc24xx(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, v
* for further processing.
*
* This is called after the individual dissect_ieee802154* functions
- * have been called to determine what sort of FCS is present.
+ * have been called to determine what sort of FCS is present, if any.
*
* @param tvb pointer to buffer containing raw packet.
* @param pinfo pointer to packet information fields
@@ -1335,17 +1325,90 @@ dissect_ieee802154_common(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, g
{
proto_tree *ieee802154_tree;
ieee802154_packet *packet;
- guint mhr_len = ieee802154_dissect_header(tvb, pinfo, tree, 0, &ieee802154_tree, &packet);
- if (!mhr_len || tvb_reported_length_remaining(tvb, mhr_len+IEEE802154_FCS_LEN) < 0 ) {
- return;
+ gboolean fcs_present;
+ gboolean fcs_ok;
+ tvbuff_t* no_fcs_tvb;
+
+ if (options & DISSECT_IEEE802154_OPTION_FCS_PRESENT) {
+ /*
+ * Well, this packet should, in theory, have an FCS.
+ * Do we have the entire packet, and does it have enough data for
+ * the FCS?
+ */
+ guint reported_len = tvb_reported_length(tvb);
+
+ if (reported_len < IEEE802154_FCS_LEN) {
+ /*
+ * The packet is claimed not to even have enough data
+ * for an FCS. Pretend it doesn't have one.
+ */
+ no_fcs_tvb = tvb;
+ fcs_present = FALSE;
+ fcs_ok = TRUE; // assume OK if not existing
+ } else {
+ /*
+ * The packet is claimed to have enough data for an FCS.
+ * Slice off the FCS from the reported length.
+ */
+ reported_len -= IEEE802154_FCS_LEN;
+ no_fcs_tvb = tvb_new_subset_length(tvb, 0, reported_len);
+
+ /*
+ * Is the FCS present in the captured data?
+ * reported_len is now the length of the packet without the
+ * FCS, so the FCS begins at an offset of reported_len.
+ */
+ if (tvb_bytes_exist(tvb, reported_len, IEEE802154_FCS_LEN)) {
+ /*
+ * Yes. Check it.
+ */
+ fcs_present = TRUE;
+ fcs_ok = options & DISSECT_IEEE802154_OPTION_CC24xx ? is_cc24xx_crc_ok(tvb) : is_fcs_ok(tvb, NULL);
+ } else {
+ /*
+ * No.
+ *
+ * Either 1) this means that there was a snapshot length
+ * in effect when the capture was done, and that sliced
+ * some or all of the FCS off or 2) this is a capture
+ * with no FCS, using the same link-layer header type
+ * value as captures with the FCS, and indicating the
+ * lack of an FCS by having the captured length be the
+ * length of the packet minus the length of the FCS
+ * and the actual length being the length of the packet
+ * including the FCS, rather than by using the "no FCS"
+ * link-layer header type.
+ *
+ * We could try to distinguish between them by checking
+ * for a captured length that's exactly IEEE802154_FCS_LEN
+ * bytes less than the actual length. That would allow
+ * us to report packets that are cut short just before,
+ * or in the middle of, the FCS as having been cut short
+ * by the snapshot length.
+ *
+ * However, we can't distinguish between a packet that
+ * happened to be cut IEEE802154_FCS_LEN bytes short
+ * due to a snapshot length being in effect when
+ * the capture was done and a packet that *wasn't*
+ * cut short by a snapshot length but that doesn't
+ * include the FCS. Let's hope that rarely happens.
+ */
+ fcs_present = FALSE;
+ fcs_ok = TRUE; // assume OK if not existing
+ }
+ }
+ } else {
+ no_fcs_tvb = tvb;
+ fcs_present = FALSE;
+ fcs_ok = TRUE; // assume OK if not existing
}
- gboolean fcs_ok = TRUE; // assume OK if not existing
- if (tvb_bytes_exist(tvb, tvb_reported_length(tvb)-IEEE802154_FCS_LEN, IEEE802154_FCS_LEN)) {
- fcs_ok = options & DISSECT_IEEE802154_OPTION_CC24xx ? is_cc24xx_crc_ok(tvb) : is_fcs_ok(tvb, NULL);
+ guint mhr_len = ieee802154_dissect_header(no_fcs_tvb, pinfo, tree, 0, &ieee802154_tree, &packet);
+ if (!mhr_len || tvb_reported_length_remaining(no_fcs_tvb, mhr_len) < 0 ) {
+ return;
}
- tvbuff_t* payload = ieee802154_decrypt_payload(tvb, mhr_len, pinfo, ieee802154_tree, packet);
+ tvbuff_t* payload = ieee802154_decrypt_payload(no_fcs_tvb, mhr_len, pinfo, ieee802154_tree, packet);
if (payload) {
guint pie_size = ieee802154_dissect_payload_ies(payload, pinfo, ieee802154_tree, packet);
payload = tvb_new_subset_remaining(payload, pie_size);
@@ -1360,7 +1423,8 @@ dissect_ieee802154_common(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, g
}
}
- ieee802154_dissect_fcs(tvb, pinfo, ieee802154_tree, options & DISSECT_IEEE802154_OPTION_CC24xx, fcs_ok);
+ if (fcs_present)
+ ieee802154_dissect_fcs(tvb, pinfo, ieee802154_tree, options & DISSECT_IEEE802154_OPTION_CC24xx, fcs_ok);
}
guint
@@ -1878,16 +1942,16 @@ ieee802154_decrypt_payload(tvbuff_t *tvb, guint mhr_len, packet_info *pinfo, pro
/* Get the unencrypted data if decryption failed. */
if (!payload_tvb) {
- /* Deal with possible truncation and the MIC and FCS fields at the end. */
- gint reported_len = tvb_reported_length(tvb)-mhr_len-rx_mic_len-IEEE802154_FCS_LEN;
+ /* Deal with possible truncation and the MIC fields at the end. */
+ gint reported_len = tvb_reported_length(tvb)-mhr_len-rx_mic_len;
gint captured_len = tvb_captured_length(tvb)-mhr_len;
payload_tvb = tvb_new_subset_length_caplen(tvb, mhr_len, MIN(captured_len, reported_len), reported_len);
}
/* Display the MIC. */
if (rx_mic_len) {
- if (tvb_bytes_exist(tvb, tvb_reported_length(tvb) - rx_mic_len - IEEE802154_FCS_LEN, rx_mic_len)) {
- proto_tree_add_item(ieee802154_tree, hf_ieee802154_mic, tvb, tvb_reported_length(tvb)-rx_mic_len-IEEE802154_FCS_LEN, rx_mic_len, ENC_NA);
+ if (tvb_bytes_exist(tvb, tvb_reported_length(tvb) - rx_mic_len, rx_mic_len)) {
+ proto_tree_add_item(ieee802154_tree, hf_ieee802154_mic, tvb, tvb_reported_length(tvb)-rx_mic_len, rx_mic_len, ENC_NA);
}
}
@@ -1942,8 +2006,8 @@ ieee802154_decrypt_payload(tvbuff_t *tvb, guint mhr_len, packet_info *pinfo, pro
}
/* Plaintext Payload. */
else {
- /* Deal with possible truncation and the MIC and FCS fields at the end. */
- gint reported_len = tvb_reported_length(tvb)-mhr_len-IEEE802154_FCS_LEN;
+ /* Deal with possible truncation and the MIC field at the end. */
+ gint reported_len = tvb_reported_length(tvb)-mhr_len;
gint captured_len = tvb_captured_length(tvb)-mhr_len;
payload_tvb = tvb_new_subset_length_caplen(tvb, mhr_len, MIN(captured_len, reported_len), reported_len);
}
@@ -2837,7 +2901,7 @@ dissect_ieee802154_header_ie(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree
packet->payload_ie_present = (id == IEEE802154_HEADER_IE_HT1);
break;
}
- } while ((tvb_reported_length_remaining(tvb, offset) > IEEE802154_MIC_LENGTH(packet->security_level) + IEEE802154_FCS_LEN + 1));
+ } while ((tvb_reported_length_remaining(tvb, offset) > IEEE802154_MIC_LENGTH(packet->security_level) + 1));
proto_item_set_len(ies_item, offset - orig_offset);
return offset - orig_offset;
@@ -3624,7 +3688,7 @@ dissect_ieee802154_decrypt(tvbuff_t *tvb,
M = IEEE802154_MIC_LENGTH(packet->security_level);
*decrypt_info->rx_mic_length = M;
- reported_len = tvb_reported_length_remaining(tvb, offset) - IEEE802154_FCS_LEN - M;
+ reported_len = tvb_reported_length_remaining(tvb, offset) - M;
if (reported_len < 0) {
*decrypt_info->status = DECRYPT_PACKET_TOO_SMALL;
return NULL;