From 222eaa14fb2bd1dde2c93cb0ac79aa29defc8c76 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Deronne?= <sebastien.deronne@gmail.com>
Date: Tue, 3 Jun 2025 20:09:31 +0200
Subject: [PATCH] network, wifi: The size of the ieee80211_radiotap_header
 should be set first for correct alignment calculations

---
 src/network/utils/radiotap-header.cc | 30 +++++++++++++++++-----------
 src/network/utils/radiotap-header.h  | 12 ++++++++++-
 src/wifi/helper/wifi-helper.cc       |  4 +++-
 3 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/src/network/utils/radiotap-header.cc b/src/network/utils/radiotap-header.cc
index 52e98c225..0cd2597f2 100644
--- a/src/network/utils/radiotap-header.cc
+++ b/src/network/utils/radiotap-header.cc
@@ -568,6 +568,20 @@ RadiotapHeader::Print(std::ostream& os) const
     }
 }
 
+void
+RadiotapHeader::SetWifiHeader(bool extended)
+{
+    NS_LOG_FUNCTION(this << extended);
+    NS_ASSERT_MSG(m_length == MIN_HEADER_SIZE,
+                  "RadiotapHeader::SetWifiHeader() should be called before any other Set* method");
+    if (extended)
+    {
+        m_present |= RADIOTAP_EXT;
+        m_presentExt = 0;
+        m_length += sizeof(RadiotapExtFlags);
+    }
+}
+
 void
 RadiotapHeader::SetTsft(uint64_t value)
 {
@@ -1028,12 +1042,8 @@ void
 RadiotapHeader::SetUsigFields(const UsigFields& usigFields)
 {
     NS_LOG_FUNCTION(this << usigFields.common << usigFields.mask << usigFields.value);
-    if (!m_presentExt)
-    {
-        m_present |= RADIOTAP_TLV | RADIOTAP_EXT;
-        m_presentExt = 0;
-        m_length += sizeof(RadiotapExtFlags);
-    }
+    NS_ASSERT_MSG(m_presentExt, "Number of it_present words is incorrect");
+    m_present |= RADIOTAP_TLV;
 
     NS_ASSERT_MSG(!(*m_presentExt & RADIOTAP_USIG), "U-SIG radiotap field already present");
     *m_presentExt |= RADIOTAP_USIG;
@@ -1094,12 +1104,8 @@ void
 RadiotapHeader::SetEhtFields(const EhtFields& ehtFields)
 {
     NS_LOG_FUNCTION(this << ehtFields.known);
-    if (!m_presentExt)
-    {
-        m_present |= RADIOTAP_TLV | RADIOTAP_EXT;
-        m_presentExt = 0;
-        m_length += sizeof(RadiotapExtFlags);
-    }
+    NS_ASSERT_MSG(m_presentExt, "Number of it_present words is incorrect");
+    m_present |= RADIOTAP_TLV;
 
     NS_ASSERT_MSG(!(*m_presentExt & RADIOTAP_EHT_SIG), "EHT radiotap field already present");
     *m_presentExt |= RADIOTAP_EHT_SIG;
diff --git a/src/network/utils/radiotap-header.h b/src/network/utils/radiotap-header.h
index 501b81130..e8a36ea08 100644
--- a/src/network/utils/radiotap-header.h
+++ b/src/network/utils/radiotap-header.h
@@ -82,6 +82,14 @@ class RadiotapHeader : public Header
      */
     void Print(std::ostream& os) const override;
 
+    /**
+     * @brief Set the ieee80211_radiotap_header. This method must be called
+     * before any other Set* method.
+     *
+     * @param extended If true, one more it_present word follows the it_present bitmask.
+     */
+    void SetWifiHeader(bool extended);
+
     /**
      * @brief Set the Time Synchronization Function Timer (TSFT) value.  Valid for
      * received frames only.
@@ -773,6 +781,8 @@ class RadiotapHeader : public Header
     void SetEhtFields(const EhtFields& ehtFields);
 
   private:
+    static constexpr int MIN_HEADER_SIZE{8}; //!< the minimum size of the radiotap header
+
     /**
      * Serialize the TSFT radiotap header.
      *
@@ -1048,7 +1058,7 @@ class RadiotapHeader : public Header
         RADIOTAP_EHT_SIG = 0x00000004
     };
 
-    uint16_t m_length{8};                   //!< entire length of radiotap data + header
+    uint16_t m_length{MIN_HEADER_SIZE};     //!< entire length of radiotap data + header
     uint32_t m_present{0};                  //!< bits describing which fields follow header
     std::optional<uint32_t> m_presentExt{}; //!< optional extended present bitmask
 
diff --git a/src/wifi/helper/wifi-helper.cc b/src/wifi/helper/wifi-helper.cc
index ab1942a42..c5b6148d4 100644
--- a/src/wifi/helper/wifi-helper.cc
+++ b/src/wifi/helper/wifi-helper.cc
@@ -346,9 +346,9 @@ WifiPhyHelper::GetRadiotapHeader(RadiotapHeader& header,
                                  uint16_t staId,
                                  SignalNoiseDbm signalNoise)
 {
+    GetRadiotapHeader(header, packet, channelFreqMhz, p20Index, txVector, aMpdu, staId);
     header.SetAntennaSignalPower(signalNoise.signal);
     header.SetAntennaNoisePower(signalNoise.noise);
-    GetRadiotapHeader(header, packet, channelFreqMhz, p20Index, txVector, aMpdu, staId);
 }
 
 void
@@ -365,6 +365,8 @@ WifiPhyHelper::GetRadiotapHeader(RadiotapHeader& header,
     const auto channelWidth = txVector.GetChannelWidth();
     const auto gi = txVector.GetGuardInterval();
 
+    header.SetWifiHeader(IsEht(preamble));
+
     header.SetTsft(Simulator::Now().GetMicroSeconds());
 
     uint8_t frameFlags = RadiotapHeader::FRAME_FLAG_NONE;