System property for changing minimum key size

Introducing a system property to allow increasing the minimum key size
from default of 7 octets.
System property: bluetooth.gap.min_key_size

Test: mmm pacakges/modules/Bluetooth
Flag: EXEMPT guarded by system property
Bug: 362624309
Change-Id: Idaa7eb191158d8487437642b2f2f7f5492619a88

7 files changed, 39 insertions, 5 deletions

diff --git a/sysprop/Android.bp b/sysprop/Android.bp
index c2e71a97c8..1b72eb4cb7 100644
--- a/sysprop/Android.bp
+++ b/sysprop/Android.bp
@@ -11,6 +11,7 @@ sysprop_library {
         "ble.sysprop",
         "bta.sysprop",
         "device_id.sysprop",
+        "gap.sysprop",
         "hfp.sysprop",
     ],
     property_owner: "Platform",
diff --git a/sysprop/BUILD.gn b/sysprop/BUILD.gn
index 09126c8df0..407b7a88fc 100644
--- a/sysprop/BUILD.gn
+++ b/sysprop/BUILD.gn
@@ -7,6 +7,7 @@ sysprop("libcom.android.sysprop.bluetooth") {
     "ble.sysprop",
     "bta.sysprop",
     "device_id.sysprop",
+    "gap.sysprop",
     "hfp.sysprop",
   ]
   deps = [ "//bt/floss/android-base:android-base" ]
diff --git a/sysprop/exported_include/android_bluetooth_sysprop.h b/sysprop/exported_include/android_bluetooth_sysprop.h
index 50553ecc5b..8d5122d8e2 100644
--- a/sysprop/exported_include/android_bluetooth_sysprop.h
+++ b/sysprop/exported_include/android_bluetooth_sysprop.h
@@ -21,4 +21,5 @@
 #include <ble.sysprop.h>
 #include <bta.sysprop.h>
 #include <device_id.sysprop.h>
+#include <gap.sysprop.h>
 #include <hfp.sysprop.h>
diff --git a/sysprop/gap.sysprop b/sysprop/gap.sysprop
new file mode 100644
index 0000000000..e9f7e00a3c
--- /dev/null
+++ b/sysprop/gap.sysprop
@@ -0,0 +1,12 @@
+module: "android.sysprop.bluetooth.Gap"
+owner: Platform
+
+prop {
+    api_name: "min_key_size"
+    type: Integer
+    scope: Internal
+    access: Readonly
+    prop_name: "bluetooth.gap.min_key_size"
+}
+
+
diff --git a/system/gd/hci/BUILD.gn b/system/gd/hci/BUILD.gn
index d7366c33b2..8f65671fd7 100644
--- a/system/gd/hci/BUILD.gn
+++ b/system/gd/hci/BUILD.gn
@@ -43,6 +43,7 @@ source_set("BluetoothHciSources") {
   deps = [
     "//bt/flags:bluetooth_flags_c_lib",
     "//bt/system/gd:gd_default_deps",
+    "//bt/sysprop:libcom.android.sysprop.bluetooth",
   ]
 
   configs += [
diff --git a/system/gd/hci/controller.cc b/system/gd/hci/controller.cc
index 3a4ab17dfb..9a3f721110 100644
--- a/system/gd/hci/controller.cc
+++ b/system/gd/hci/controller.cc
@@ -16,6 +16,7 @@
 
 #include "hci/controller.h"
 
+#include <android_bluetooth_sysprop.h>
 #include <bluetooth/log.h>
 #include <com_android_bluetooth_flags.h>
 
@@ -39,7 +40,9 @@
 namespace bluetooth {
 namespace hci {
 
-constexpr uint8_t kMinEncryptionKeySize = 7;  // #define MIN_ENCRYPTION_KEY_SIZE 7
+constexpr int kMinEncryptionKeySize = 7;
+constexpr int kMinEncryptionKeySizeDefault = kMinEncryptionKeySize;
+constexpr int kMaxEncryptionKeySize = 16;
 
 constexpr bool kDefaultVendorCapabilitiesEnabled = true;
 static const std::string kPropertyVendorCapabilitiesEnabled =
@@ -107,8 +110,13 @@ struct Controller::impl {
             handler->BindOnceOn(this, &Controller::impl::read_buffer_size_complete_handler));
 
     if (is_supported(OpCode::SET_MIN_ENCRYPTION_KEY_SIZE)) {
+      uint8_t min_key_size =
+              (uint8_t)std::min(std::max(android::sysprop::bluetooth::Gap::min_key_size().value_or(
+                                                 kMinEncryptionKeySizeDefault),
+                                         kMinEncryptionKeySize),
+                                kMaxEncryptionKeySize);
       hci_->EnqueueCommand(
-              SetMinEncryptionKeySizeBuilder::Create(kMinEncryptionKeySize),
+              SetMinEncryptionKeySizeBuilder::Create(min_key_size),
               handler->BindOnceOn(this, &Controller::impl::set_min_encryption_key_size_handler));
     }
 
diff --git a/system/stack/btm/btm_sec.cc b/system/stack/btm/btm_sec.cc
index d458bf79a8..e647715e40 100644
--- a/system/stack/btm/btm_sec.cc
+++ b/system/stack/btm/btm_sec.cc
@@ -26,6 +26,7 @@
 
 #include "stack/btm/btm_sec.h"
 
+#include <android_bluetooth_sysprop.h>
 #include <base/functional/bind.h>
 #include <base/strings/stringprintf.h>
 #include <bluetooth/log.h>
@@ -3365,7 +3366,16 @@ void btm_sec_encrypt_change(uint16_t handle, tHCI_STATUS status, uint8_t encr_en
   }
 }
 
-constexpr uint8_t MIN_KEY_SIZE = 7;
+constexpr int MIN_KEY_SIZE = 7;
+constexpr int MIN_KEY_SIZE_DEFAULT = MIN_KEY_SIZE;
+constexpr int MAX_KEY_SIZE = 16;
+static uint8_t get_min_enc_key_size() {
+  static uint8_t min_key_size = (uint8_t)std::min(
+          std::max(android::sysprop::bluetooth::Gap::min_key_size().value_or(MIN_KEY_SIZE_DEFAULT),
+                   MIN_KEY_SIZE),
+          MAX_KEY_SIZE);
+  return min_key_size;
+}
 
 static void read_encryption_key_size_complete_after_encryption_change(uint8_t status,
                                                                       uint16_t handle,
@@ -3386,7 +3396,7 @@ static void read_encryption_key_size_complete_after_encryption_change(uint8_t st
     return;
   }
 
-  if (key_size < MIN_KEY_SIZE) {
+  if (key_size < get_min_enc_key_size()) {
     log::error("encryption key too short, disconnecting. handle:0x{:x},key_size:{}", handle,
                key_size);
 
@@ -3961,7 +3971,7 @@ static void read_encryption_key_size_complete_after_key_refresh(uint8_t status,
     return;
   }
 
-  if (key_size < MIN_KEY_SIZE) {
+  if (key_size < get_min_enc_key_size()) {
     log::error("encryption key too short, disconnecting. handle: 0x{:x} key_size {}", handle,
                key_size);