From 1072a897f5c17f2d13de16450059baa81c61d525 Mon Sep 17 00:00:00 2001
From: Marcus Holland-Moritz <mhx@fb.com>
Date: Tue, 17 May 2016 13:08:17 -0700
Subject: [PATCH] folly: fbvector: ubsan: don't call memcpy() with nullptr args
 if size == 0

Reviewed By: meyering, luciang

Differential Revision: D3310683

fbshipit-source-id: c86471d54062b2f3455f15fb73340fac486d9e44
---
 folly/FBVector.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/folly/FBVector.h b/folly/FBVector.h
index fb611e56c1e..036882a4930 100644
--- a/folly/FBVector.h
+++ b/folly/FBVector.h
@@ -522,7 +522,9 @@ class fbvector : private boost::totally_ordered<fbvector<T, Allocator>> {
 
   static void
   S_uninitialized_copy_bits(T* dest, const T* first, const T* last) {
-    std::memcpy((void*)dest, (void*)first, (last - first) * sizeof(T));
+    if (last != first) {
+      std::memcpy((void*)dest, (void*)first, (last - first) * sizeof(T));
+    }
   }
 
   static void
@@ -530,7 +532,9 @@ class fbvector : private boost::totally_ordered<fbvector<T, Allocator>> {
                        std::move_iterator<T*> last) {
     T* bFirst = first.base();
     T* bLast = last.base();
-    std::memcpy((void*)dest, (void*)bFirst, (bLast - bFirst) * sizeof(T));
+    if (bLast != bFirst) {
+      std::memcpy((void*)dest, (void*)bFirst, (bLast - bFirst) * sizeof(T));
+    }
   }
 
   template <typename It>