From 367aedc0e9bcd6a667a86fa0fe58d84dd974d1f4 Mon Sep 17 00:00:00 2001
From: Matthias Ringwald <matthias@ringwald.ch>
Date: Sat, 19 Jun 2021 17:58:56 +0200
Subject: [PATCH] gap: send user confirmation negative reply if required
 security level cannot be met

---
 src/hci.c | 46 +++++++++++++++++++++++-----------------------
 src/hci.h | 17 +++++++++--------
 2 files changed, 32 insertions(+), 31 deletions(-)

diff --git a/src/hci.c b/src/hci.c
index 3d8587212..db60d5cfa 100644
--- a/src/hci.c
+++ b/src/hci.c
@@ -2395,22 +2395,6 @@ static bool hci_ssp_security_level_possible_for_io_cap(gap_security_level_t leve
     // LEVEL 2 requires SSP, which is a given
     return true;
 }
-
-static bool hci_ssp_validate_possible_security_level(bd_addr_t addr){
-    hci_connection_t * conn = hci_connection_for_bd_addr_and_type(addr, BD_ADDR_TYPE_ACL);
-    if (!conn) return false;
-    // abort pairing, if requested security level cannot be met
-    if (hci_ssp_security_level_possible_for_io_cap(conn->requested_security_level, hci_stack->ssp_io_capability, conn->io_cap_response_io)) {
-        // inlined hci_add_connection_flags_for_flipped_bd_addr
-        hci_connection_timestamp(conn);
-        return true;
-    } else {
-        log_info("Level %u cannot be reached", conn->requested_security_level);
-        conn->bonding_flags |= BONDING_DISCONNECT_SECURITY_BLOCK;
-        return false;
-    };
-}
-
 #endif
 
 static void event_handler(uint8_t *packet, uint16_t size){
@@ -2801,16 +2785,26 @@ static void event_handler(uint8_t *packet, uint16_t size){
 
         case HCI_EVENT_USER_CONFIRMATION_REQUEST:
             hci_event_user_confirmation_request_get_bd_addr(packet, addr);
-            if (hci_ssp_validate_possible_security_level(addr) == false) break;
-            if (!hci_stack->ssp_auto_accept) break;
-            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], AUTH_FLAG_SEND_USER_CONFIRM_REPLY);
+            conn = hci_connection_for_bd_addr_and_type(addr, BD_ADDR_TYPE_ACL);
+            if (!conn) break;
+            if (hci_ssp_security_level_possible_for_io_cap(conn->requested_security_level, hci_stack->ssp_io_capability, conn->io_cap_response_io)) {
+                if (hci_stack->ssp_auto_accept){
+                    hci_add_connection_flags_for_flipped_bd_addr(&packet[2], AUTH_FLAG_SEND_USER_CONFIRM_REPLY);
+                };
+            } else {
+                hci_pairing_complete(conn, ERROR_CODE_INSUFFICIENT_SECURITY);
+                hci_add_connection_flags_for_flipped_bd_addr(&packet[2], AUTH_FLAG_SEND_USER_CONFIRM_NEGATIVE_REPLY);
+                // don't forward event to app
+                hci_run();
+                return;
+            }
             break;
 
         case HCI_EVENT_USER_PASSKEY_REQUEST:
-            hci_event_user_passkey_request_get_bd_addr(packet, addr);
-            if (hci_ssp_validate_possible_security_level(addr) == false) break;
-            if (!hci_stack->ssp_auto_accept) break;
-            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], AUTH_FLAG_SEND_USER_PASSKEY_REPLY);
+            // Pairing using Passkey results in MITM protection. If Level 4 is required, support for SC is validated on IO Cap Request
+            if (hci_stack->ssp_auto_accept){
+                hci_add_connection_flags_for_flipped_bd_addr(&packet[2], AUTH_FLAG_SEND_USER_PASSKEY_REPLY);
+            };
             break;
 
         case HCI_EVENT_MODE_CHANGE:
@@ -4610,6 +4604,12 @@ static bool hci_run_general_pending_commands(void){
             return true;
         }
 
+        if (connection->authentication_flags & AUTH_FLAG_SEND_USER_CONFIRM_NEGATIVE_REPLY){
+            connectionClearAuthenticationFlags(connection, AUTH_FLAG_SEND_USER_CONFIRM_NEGATIVE_REPLY);
+            hci_send_cmd(&hci_user_confirmation_request_negative_reply, &connection->address);
+            return true;
+        }
+
         if (connection->authentication_flags & AUTH_FLAG_SEND_USER_PASSKEY_REPLY){
             connectionClearAuthenticationFlags(connection, AUTH_FLAG_SEND_USER_PASSKEY_REPLY);
             hci_send_cmd(&hci_user_passkey_request_reply, &connection->address, 000000);
diff --git a/src/hci.h b/src/hci.h
index 866cd29fd..e38f06ce9 100644
--- a/src/hci.h
+++ b/src/hci.h
@@ -205,23 +205,24 @@ typedef enum {
     AUTH_FLAG_SEND_IO_CAPABILITIES_REPLY          = 0x0008,
     AUTH_FLAG_SEND_IO_CAPABILITIES_NEGATIVE_REPLY = 0x0010,
     AUTH_FLAG_SEND_USER_CONFIRM_REPLY             = 0x0020,
-    AUTH_FLAG_SEND_USER_PASSKEY_REPLY             = 0x0040,
+    AUTH_FLAG_SEND_USER_CONFIRM_NEGATIVE_REPLY    = 0x0040,
+    AUTH_FLAG_SEND_USER_PASSKEY_REPLY             = 0x0080,
 
     // Classic OOB
-    AUTH_FLAG_SEND_REMOTE_OOB_DATA_REPLY          = 0x0080,
+    AUTH_FLAG_SEND_REMOTE_OOB_DATA_REPLY          = 0x0100,
 
     // pairing status
-    AUTH_FLAG_LEGACY_PAIRING_ACTIVE               = 0x0100,
-    AUTH_FLAG_SSP_PAIRING_ACTIVE                  = 0x0200,
+    AUTH_FLAG_LEGACY_PAIRING_ACTIVE               = 0x0200,
+    AUTH_FLAG_SSP_PAIRING_ACTIVE                  = 0x0400,
     AUTH_FLAG_PAIRING_ACTIVE_MASK                 = (AUTH_FLAG_LEGACY_PAIRING_ACTIVE | AUTH_FLAG_SSP_PAIRING_ACTIVE),
 
     // connection status
-    AUTH_FLAG_CONNECTION_AUTHENTICATED            = 0x0400,
-    AUTH_FLAG_CONNECTION_ENCRYPTED                = 0x0800,
+    AUTH_FLAG_CONNECTION_AUTHENTICATED            = 0x0800,
+    AUTH_FLAG_CONNECTION_ENCRYPTED                = 0x1000,
 
     // errands
-    AUTH_FLAG_READ_RSSI                           = 0x1000,
-    AUTH_FLAG_WRITE_SUPERVISION_TIMEOUT           = 0x2000,
+    AUTH_FLAG_READ_RSSI                           = 0x2000,
+    AUTH_FLAG_WRITE_SUPERVISION_TIMEOUT           = 0x4000,
 
 } hci_authentication_flags_t;