From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Brian Delwiche <delwiche@google.com>
Date: Mon, 22 Apr 2024 21:14:56 +0000
Subject: [PATCH] Fix an authentication bypass bug in SMP

When pairing with BLE legacy pairing initiated
from remote, authentication can be bypassed.
This change fixes it.

Bug: 251514170
Test: m com.android.btservices
Test: manual run against PoC
Ignore-AOSP-First: security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:8a3dbadc71428a30b172a74343be08498c656747)
Merged-In: I66b1f9a80060f48a604001829db8ea7c96c7b7f8
Change-Id: I66b1f9a80060f48a604001829db8ea7c96c7b7f8
---
 stack/smp/smp_act.cc | 12 ++++++++++++
 stack/smp/smp_int.h  |  1 +
 2 files changed, 13 insertions(+)

diff --git a/stack/smp/smp_act.cc b/stack/smp/smp_act.cc
index f530218fb..05e0b91a4 100644
--- a/stack/smp/smp_act.cc
+++ b/stack/smp/smp_act.cc
@@ -281,6 +281,7 @@ void smp_send_pair_rsp(tSMP_CB* p_cb, tSMP_INT_DATA* p_data) {
 void smp_send_confirm(tSMP_CB* p_cb, tSMP_INT_DATA* p_data) {
   SMP_TRACE_DEBUG("%s", __func__);
   smp_send_cmd(SMP_OPCODE_CONFIRM, p_cb);
+  p_cb->flags |= SMP_PAIR_FLAGS_CMD_CONFIRM_SENT;
 }
 
 /*******************************************************************************
@@ -639,6 +640,17 @@ void smp_proc_init(tSMP_CB* p_cb, tSMP_INT_DATA* p_data) {
     return;
   }
 
+  if (!((p_cb->loc_auth_req & SMP_SC_SUPPORT_BIT) &&
+        (p_cb->peer_auth_req & SMP_SC_SUPPORT_BIT)) &&
+      !(p_cb->flags & SMP_PAIR_FLAGS_CMD_CONFIRM_SENT)) {
+    // in legacy pairing, the peer should send its rand after
+    // we send our confirm
+    tSMP_INT_DATA smp_int_data{};
+    smp_int_data.status = SMP_INVALID_PARAMETERS;
+    smp_sm_event(p_cb, SMP_AUTH_CMPL_EVT, &smp_int_data);
+    return;
+  }
+
   /* save the SRand for comparison */
   STREAM_TO_ARRAY(p_cb->rrand, p, BT_OCTET16_LEN);
 }
diff --git a/stack/smp/smp_int.h b/stack/smp/smp_int.h
index e0e27a4b2..3ccb4ad6f 100644
--- a/stack/smp/smp_int.h
+++ b/stack/smp/smp_int.h
@@ -240,6 +240,7 @@ typedef union {
   (1 << 7) /* used to resolve race condition */
 #define SMP_PAIR_FLAG_HAVE_LOCAL_PUBL_KEY \
   (1 << 8) /* used on slave to resolve race condition */
+#define SMP_PAIR_FLAGS_CMD_CONFIRM_SENT (1 << 9)
 
 /* check if authentication requirement need MITM protection */
 #define SMP_NO_MITM_REQUIRED(x) (((x)&SMP_AUTH_YN_BIT) == 0)