commit 16f64798a41593b4c0927ccd9914a1528ec6b0f5
author Steven Moreland <smoreland@google.com> Fri May 17 13:14:06 2019 -0700
committer Nikoli Cartagena <dargeren@google.com> Mon Jun 10 14:52:47 2019 -0700
tree 382be37f690133b84896087d5aebca75cea48b24
parent 67d92f3bbc9829672b3b3092fb6a97d4d760a51f

libbinder: readCString: no ubsan sub-overflow

Bug: 131859347
Test: fuzzer
Change-Id: I95a0f59684a172925f1eab97ff21e5d14bc79cc8
Merged-In: I95a0f59684a172925f1eab97ff21e5d14bc79cc8
(cherry picked from commit d0d4b584fc294d2c124385644099852918416344)

libs/binder/Parcel.cpp

diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index 9d96dd6..ca8277d 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -2013,8 +2013,8 @@
 
 const char* Parcel::readCString() const
 {
-    const size_t avail = mDataSize-mDataPos;
-    if (avail > 0) {
+    if (mDataPos < mDataSize) {
+        const size_t avail = mDataSize-mDataPos;
         const char* str = reinterpret_cast<const char*>(mData+mDataPos);
         // is the string's trailing NUL within the parcel's valid bounds?
         const char* eos = reinterpret_cast<const char*>(memchr(str, 0, avail));