From dd8497fb53f6faa0f15ae33f410a78b5ef4245e1 Mon Sep 17 00:00:00 2001
From: Matteo Cypriani <matteo.cypriani@uqat.ca>
Date: Thu, 20 Mar 2014 14:53:58 -0400
Subject: [PATCH] [Listener] Radiotap: handle Extended Present Flags

Check the 31st bit of the Present Flags field, i.e. the Ext bit, set
when additional Present Flags fields follow.
---
 owlps-listener/owlps-listener.h  |  7 +++++--
 owlps-listener/owlps-listenerd.c | 24 +++++++++++++++++++++---
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/owlps-listener/owlps-listener.h b/owlps-listener/owlps-listener.h
index 34bd31a..a5fbddf 100644
--- a/owlps-listener/owlps-listener.h
+++ b/owlps-listener/owlps-listener.h
@@ -140,8 +140,11 @@ enum {MODE_ACTIVE = 'a', MODE_PASSIVE = 'p', MODE_MIXED = 'm'} ;
 #define RTAP_CHANNEL 3 // Channel frequency and flags
 #define RTAP_FHSS 4 // FHSS hop set and hop pattern
 #define RTAP_ANTENNASIGNAL 5
-// ... (we use only the antenna signal field, so we don't need to handle
-// the bits greater than RTAP_ANTENNASIGNAL)
+/* We use only the first Antenna Signal field, so we don't need to handle
+ * the bits greater than RTAP_ANTENNASIGNAL, except for the Ext bit
+ * (Extended Presence), to be able to jump after all the Present Flags
+ * fields: */
+#define RTAP_EXT 31
 
 /* Lengths of the radiotap optional fields (in bytes) */
 #define RTAP_L_TSFT 8 // MAC timestamp (Time Synchronization Function Timer)
diff --git a/owlps-listener/owlps-listenerd.c b/owlps-listener/owlps-listenerd.c
index 63b61e9..60d9e8d 100644
--- a/owlps-listener/owlps-listenerd.c
+++ b/owlps-listener/owlps-listenerd.c
@@ -1332,15 +1332,33 @@ bool extract_radiotap_ss(const u_char *const pkt_data,
 {
   uint32_t rtap_presentflags ;
   uint_fast16_t rtap_position ;
+  bool rtap_ext ;
 
-  // Get rtap flags:
+  // Get the first Present Flags field from the Radiotap header:
   memcpy(&rtap_presentflags,
          &pkt_data[RTAP_P_PRESENTFLAGS], RTAP_L_PRESENTFLAGS) ;
   // The Radiotap header is little-endian
   rtap_presentflags = le32toh(rtap_presentflags) ;
 
-  // The fields dependent on present flags start at byte 8
-  rtap_position = 8 ;
+  // The optional fields start right after the Present Flags field:
+  rtap_position =
+    RTAP_L_HREVISION + RTAP_L_HPAD +
+    RTAP_L_HLENGTH + RTAP_L_PRESENTFLAGS ;
+
+  // Skip the potential additional Present Flags fields:
+  rtap_ext = FIELD_PRESENT(rtap_presentflags, RTAP_EXT) ;
+  while (rtap_ext)
+    {
+      // Get the additional Present Flags field:
+      uint32_t rtap_presentflags_ext ;
+      memcpy(&rtap_presentflags_ext,
+             &pkt_data[rtap_position], RTAP_L_PRESENTFLAGS) ;
+      rtap_presentflags_ext = le32toh(rtap_presentflags_ext) ;
+      // Check if there is another one after it:
+      rtap_ext = FIELD_PRESENT(rtap_presentflags_ext, RTAP_EXT) ;
+      // Skip the current field:
+      rtap_position += SKIP_FIELD(rtap_position, RTAP_L_PRESENTFLAGS) ;
+    }
 
   // Test the first bits of the flag field in order to check their
   // presence, up to the antenna signal field which is the only one