From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Brian Delwiche <delwiche@google.com>
Date: Thu, 1 Jun 2023 23:57:58 +0000
Subject: [PATCH] Fix UAF in gatt_cl.cc

gatt_cl.cc accesses a header field after the buffer holding it may have
been freed.

Track the relevant state as a local variable instead.

Bug: 274617156
Test: atest: bluetooth, validated against fuzzer
Tag: #security
Ignore-AOSP-First: Security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d7a7f7f3311202065de4b2c17b49994053dd1244)
Merged-In: I085ecfa1a9ba098ecbfecbd3cb3e263ae13f9724
Change-Id: I085ecfa1a9ba098ecbfecbd3cb3e263ae13f9724
---
 stack/gatt/gatt_cl.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/stack/gatt/gatt_cl.cc b/stack/gatt/gatt_cl.cc
index 203808806..49ccc7e52 100644
--- a/stack/gatt/gatt_cl.cc
+++ b/stack/gatt/gatt_cl.cc
@@ -582,12 +582,17 @@ void gatt_process_prep_write_rsp(tGATT_TCB& tcb, tGATT_CLCB* p_clcb,
 
   memcpy(value.value, p, value.len);
 
+  bool subtype_is_write_prepare = (p_clcb->op_subtype == GATT_WRITE_PREPARE);
+
   if (!gatt_check_write_long_terminate(tcb, p_clcb, &value)) {
     gatt_send_prepare_write(tcb, p_clcb);
     return;
   }
 
-  if (p_clcb->op_subtype == GATT_WRITE_PREPARE) {
+  // We now know that we have not terminated, or else we would have returned
+  // early.  We free the buffer only if the subtype is not equal to
+  // GATT_WRITE_PREPARE, so checking here is adequate to prevent UAF.
+  if (subtype_is_write_prepare) {
     /* application should verify handle offset
        and value are matched or not */
     gatt_end_operation(p_clcb, p_clcb->status, &value);
