[ASan] fix a bug in allocator-v2 which could lead to SEGV on realloc(malloc(0), 4)

llvm-svn: 173681

2 files changed, 10 insertions, 1 deletions

diff --git a/compiler-rt/lib/asan/asan_allocator2.cc b/compiler-rt/lib/asan/asan_allocator2.cc
index 63cb41b4c97..eae4bf5ee0d 100644
--- a/compiler-rt/lib/asan/asan_allocator2.cc
+++ b/compiler-rt/lib/asan/asan_allocator2.cc
@@ -612,7 +612,7 @@ void *asan_calloc(uptr nmemb, uptr size, StackTrace *stack) {
 }
 
 void *asan_realloc(void *p, uptr size, StackTrace *stack) {
-  if (p == 0)
+  if (p == 0 || reinterpret_cast<uptr>(p) == kReturnOnZeroMalloc)
     return Allocate(size, 8, stack, FROM_MALLOC);
   if (size == 0) {
     Deallocate(p, stack, FROM_MALLOC);
diff --git a/compiler-rt/lib/asan/tests/asan_test.cc b/compiler-rt/lib/asan/tests/asan_test.cc
index 487ed97a574..f7b6097e4bf 100644
--- a/compiler-rt/lib/asan/tests/asan_test.cc
+++ b/compiler-rt/lib/asan/tests/asan_test.cc
@@ -380,6 +380,15 @@ TEST(AddressSanitizer, ReallocTest) {
         (my_rand() % 1000 + kMinElem) * sizeof(int));
     EXPECT_EQ(3, ptr[3]);
   }
+  free(ptr);
+  // Realloc pointer returned by malloc(0).
+  int *ptr2 = Ident((int*)malloc(0));
+  fprintf(stderr, "Malloc(0): %p\n", ptr2);
+  ptr2 = Ident((int*)realloc(ptr2, sizeof(*ptr2)));
+  fprintf(stderr, "Realloc(0, 4): %p\n", ptr2);
+  *ptr2 = 42;
+  EXPECT_EQ(42, *ptr2);
+  free(ptr2);
 }
 
 #ifndef __APPLE__