Re: tcpdump: decode 802.11 QoS frames correctly

[Stefan Sperling]

On Sun, Jan 31, 2016 at 12:53:09PM +0100, Stefan Sperling wrote:
> This matters for frames which arrived in A-MPDUs.
> 
> Before:
> 
> 12:35:07.726898 802.11: QoS data: 00:1e:52:f1:80:55 sap 00 > 
> 58:94:6b:06:70:04 sap 06 I (s=85,r=85,C) len=82
> 
> After:
> 
> 12:49:08.879003 802.11: QoS data: 10.197.84.33 > 10.0.1.3: icmp: echo reply

Missed another case further down.

Index: print-802_11.c
===================================================================
RCS file: /cvs/src/usr.sbin/tcpdump/print-802_11.c,v
retrieving revision 1.28
diff -u -p -r1.28 print-802_11.c
--- print-802_11.c      12 Jan 2016 09:28:10 -0000      1.28
+++ print-802_11.c      31 Jan 2016 12:19:55 -0000
@@ -153,14 +153,21 @@ int
 ieee80211_data(struct ieee80211_frame *wh, u_int len)
 {
        u_int8_t *t = (u_int8_t *)wh;
-       struct ieee80211_frame_addr4 *w4;
        u_int datalen;
        int data = !(wh->i_fc[0] & IEEE80211_FC0_SUBTYPE_NODATA);
+       int hasqos = ((wh->i_fc[0] &
+           (IEEE80211_FC0_TYPE_MASK | IEEE80211_FC0_SUBTYPE_QOS)) ==
+           (IEEE80211_FC0_TYPE_DATA | IEEE80211_FC0_SUBTYPE_QOS));
        u_char *esrc = NULL, *edst = NULL;
 
        TCHECK(*wh);
-       t += sizeof(struct ieee80211_frame);
-       datalen = len - sizeof(struct ieee80211_frame);
+       if (hasqos) {
+               t += sizeof(struct ieee80211_qosframe);
+               datalen = len - sizeof(struct ieee80211_qosframe);
+       } else {
+               t += sizeof(struct ieee80211_frame);
+               datalen = len - sizeof(struct ieee80211_frame);
+       }
 
        switch (wh->i_fc[1] & IEEE80211_FC1_DIR_MASK) {
        case IEEE80211_FC1_DIR_TODS:
@@ -176,12 +183,25 @@ ieee80211_data(struct ieee80211_frame *w
                edst = wh->i_addr1;
                break;
        case IEEE80211_FC1_DIR_DSTODS:
-               w4 = (struct ieee80211_frame_addr4 *) wh;
-               TCHECK(*w4);
-               t = (u_int8_t *) (w4 + 1);
-               datalen = len - sizeof(*w4);
-               esrc = w4->i_addr4;
-               edst = w4->i_addr3;
+               if (hasqos) {
+                       struct ieee80211_qosframe_addr4 *w4;
+
+                       w4 = (struct ieee80211_qosframe_addr4 *) wh;
+                       TCHECK(*w4);
+                       t = (u_int8_t *) (w4 + 1);
+                       datalen = len - sizeof(*w4);
+                       esrc = w4->i_addr4;
+                       edst = w4->i_addr3;
+               } else {
+                       struct ieee80211_frame_addr4 *w4;
+
+                       w4 = (struct ieee80211_frame_addr4 *) wh;
+                       TCHECK(*w4);
+                       t = (u_int8_t *) (w4 + 1);
+                       datalen = len - sizeof(*w4);
+                       esrc = w4->i_addr4;
+                       edst = w4->i_addr3;
+               }
                break;
        }