From 465e3f3112a9c158aa6dd2f8b9439ae6c2de336f Mon Sep 17 00:00:00 2001
From: Ivan Solovev <ivan.solovev@qt.io>
Date: Thu, 02 Jan 2025 16:48:49 +0100
Subject: [PATCH] QLowEnergyControllerPrivateBluez: guard against malformed replies

The QLowEnergyControllerPrivateBluez::l2cpReadyRead() slot reads the
data from a Bluetooth L2CAP socket and then tries to process it
according to ATT protocol specs.

However, the code was missing length and sanity checks at some
codepaths in processUnsolicitedReply() and processReply() helper
methods, simply relying on the data to be in the proper format.

This patch adds some minimal checks to make sure that we do not read
past the end of the received array and do not divide by zero.

This problem was originally pointed out by Marc Mutz in an unrelated
patch.

Pick-to: 6.5 5.15
Change-Id: I8dcfe031f70ad61fa3d87dc9d771c3fabc6d0edc
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
(cherry picked from commit aecbd657c841a2a8c74631ceac96b8ff1f03ab5c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 53e991671f725c136e9aa824c59ec13934c63fb4)
---

diff --git a/src/bluetooth/qlowenergycontroller_bluez.cpp b/src/bluetooth/qlowenergycontroller_bluez.cpp
index 6f0c985..2bd0cb6 100644
--- src/bluetooth/qlowenergycontroller_bluez.cpp.orig
+++ src/bluetooth/qlowenergycontroller_bluez.cpp
@@ -64,14 +64,15 @@

 const int maxPrepareQueueSize = 1024;

-static void dumpErrorInformation(const QByteArray &response)
+/* returns false if the format is incorrect */
+static bool dumpErrorInformation(const QByteArray &response)
 {
     const char *data = response.constData();
     if (response.size() != 5
         || (static_cast<QBluezConst::AttCommand>(data[0])
             != QBluezConst::AttCommand::ATT_OP_ERROR_RESPONSE)) {
         qCWarning(QT_BT_BLUEZ) << QLatin1String("Not a valid error response");
-        return;
+        return false;
     }

     QBluezConst::AttCommand lastCommand = static_cast<QBluezConst::AttCommand>(data[1]);
@@ -126,6 +127,8 @@

     qCDebug(QT_BT_BLUEZ) << "Error:" << errorCode << "Error description:" << errorString
                          << "last command:" << lastCommand << "handle:" << handle;
+
+    return true;
 }

 static int getUuidSize(const QBluetoothUuid &uuid)
@@ -903,6 +906,7 @@
 {
     Q_ASSERT(charData);
     Q_ASSERT(data);
+    Q_ASSERT(elementLength >= 5);

     QLowEnergyHandle attributeHandle = bt_get_le16(&data[0]);
     charData->properties =
@@ -912,7 +916,7 @@
     // Bluetooth LE data comes as little endian
     if (elementLength == 7) // 16 bit uuid
         charData->uuid = QBluetoothUuid(bt_get_le16(&data[5]));
-    else
+    else if (elementLength == 21) // 128 bit uuid
         charData->uuid = QUuid::fromBytes(&data[5], QSysInfo::LittleEndian);

     qCDebug(QT_BT_BLUEZ) << "Found handle:" << Qt::hex << attributeHandle
@@ -929,6 +933,7 @@
 {
     Q_ASSERT(foundServices);
     Q_ASSERT(data);
+    Q_ASSERT(elementLength >= 6);

     QLowEnergyHandle attributeHandle = bt_get_le16(&data[0]);

@@ -938,9 +943,14 @@
     // data[2] -> included service start handle
     // data[4] -> included service end handle

+    // TODO: Spec v. 5.3, Vol. 3, Part G, 4.5.1 mentions that only
+    // 16-bit UUID can be returned here. If the UUID is 128-bit,
+    // then it is omitted from the response, and should be requested
+    // separately with the ATT_READ_REQ command.
+
     if (elementLength == 8) //16 bit uuid
         foundServices->append(QBluetoothUuid(bt_get_le16(&data[6])));
-    else
+    else if (elementLength == 22) // 128 bit uuid
         foundServices->append(QUuid::fromBytes(&data[6], QSysInfo::LittleEndian));

     qCDebug(QT_BT_BLUEZ) << "Found included service: " << Qt::hex
@@ -949,17 +959,29 @@
     return attributeHandle;
 }

+Q_DECL_COLD_FUNCTION
+static void reportMalformedData(QBluezConst::AttCommand cmd, const QByteArray &response)
+{
+    qCDebug(QT_BT_BLUEZ, "%s malformed data: %s", qt_getEnumName(cmd),
+            response.toHex().constData());
+}
+
 void QLowEnergyControllerPrivateBluez::processReply(
         const Request &request, const QByteArray &response)
 {
     Q_Q(QLowEnergyController);

+    // We already have an isEmpty() check at the only calling site that reads
+    // incoming data, so Q_ASSERT is enough.
+    Q_ASSERT(!response.isEmpty());
+
     QBluezConst::AttCommand command = static_cast<QBluezConst::AttCommand>(response.constData()[0]);

     bool isErrorResponse = false;
     // if error occurred 2. byte is previous request type
     if (command == QBluezConst::AttCommand::ATT_OP_ERROR_RESPONSE) {
-        dumpErrorInformation(response);
+        if (!dumpErrorInformation(response))
+            return;
         command = static_cast<QBluezConst::AttCommand>(response.constData()[1]);
         isErrorResponse = true;
     }
@@ -972,6 +994,10 @@
         if (isErrorResponse) {
             mtuSize = ATT_DEFAULT_LE_MTU;
         } else {
+            if (response.size() < 3) {
+                reportMalformedData(command, response);
+                break;
+            }
             const char *data = response.constData();
             quint16 mtu = bt_get_le16(&data[1]);
             mtuSize = mtu;
@@ -1000,8 +1026,15 @@
             break;
         }

+        // response[1] == elementLength. According to the spec it should be
+        // at least 4 bytes. See Spec v5.3, Vol 3, Part F, 3.4.4.10
+        if (response.size() < 2 || response[1] < 4) {
+            reportMalformedData(command, response);
+            break;
+        }
+
         QLowEnergyHandle start = 0, end = 0;
-        const quint16 elementLength = response.constData()[1];
+        const quint16 elementLength = response.constData()[1]; // value checked above
         const quint16 numElements = (response.size() - 2) / elementLength;
         quint16 offset = 2;
         const char *data = response.constData();
@@ -1077,16 +1110,25 @@
         }

         /* packet format:
-         * if GATT_CHARACTERISTIC discovery
+         * if GATT_CHARACTERISTIC discovery (Spec 5.3, Vol. 3, Part G, 4.6)
          *      <opcode><elementLength>
          *          [<handle><property><charHandle><uuid>]+
+         * The minimum elementLength is 7 bytes (uuid is always included)
          *
-         * if GATT_INCLUDE discovery
+         * if GATT_INCLUDE discovery (Spec 5.3, Vol. 3, Part G, 4.5.1)
          *      <opcode><elementLength>
          *          [<handle><startHandle_included><endHandle_included><uuid>]+
+         *  The minimum elementLength is 6 bytes (uuid can be omitted).
          *
          *  The uuid can be 16 or 128 bit.
          */
+
+        const quint8 minimumElementLength = attributeType == GATT_CHARACTERISTIC ? 7 : 6;
+        if (response.size() < 2 || response[1] < minimumElementLength) {
+            reportMalformedData(command, response);
+            break;
+        }
+
         QLowEnergyHandle lastHandle;
         const quint16 elementLength = response.constData()[1];
         const quint16 numElements = (response.size() - 2) / elementLength;
@@ -1283,6 +1325,12 @@
             break;
         }

+        // Spec 5.3, Vol. 3, Part F, 3.4.3.2
+        if (response.size() < 6) {
+            reportMalformedData(command, response);
+            break;
+        }
+
         const quint8 format = response[1];
         quint16 elementLength;
         switch (format) {
@@ -1720,9 +1768,18 @@

 void QLowEnergyControllerPrivateBluez::processUnsolicitedReply(const QByteArray &payload)
 {
+    Q_ASSERT(!payload.isEmpty());
+
     const char *data = payload.constData();
-    bool isNotification = (static_cast<QBluezConst::AttCommand>(data[0])
+    const auto command = static_cast<QBluezConst::AttCommand>(data[0]);
+    bool isNotification = (command
                            == QBluezConst::AttCommand::ATT_OP_HANDLE_VAL_NOTIFICATION);
+
+    if (payload.size() < 3) {
+        reportMalformedData(command, payload);
+        return;
+    }
+
     const QLowEnergyHandle changedHandle = bt_get_le16(&data[1]);

     if (QT_BT_BLUEZ().isDebugEnabled()) {
