[lsan] malloc_usable_size returns 0 for nullptr

compiler-rt/lib/lsan/lsan_allocator.cpp

@@ -146,6 +146,8 @@ void GetAllocatorCacheRange(uptr *begin, uptr *end) {
 }
 
 uptr GetMallocUsableSize(const void *p) {
+  if (!p)
+    return 0;
   ChunkMetadata *m = Metadata(p);
   if (!m) return 0;
   return m->requested_size;

compiler-rt/test/sanitizer_common/TestCases/Linux/malloc_usable_size.c

@@ -0,0 +1,21 @@
+// RUN: %clang -O2 %s -o %t && %run %t
+
+// Ubsan does not provide allocator.
+// UNSUPPORTED: ubsan
+
+#include <assert.h>
+#include <malloc.h>
+#include <sanitizer/allocator_interface.h>
+#include <stdlib.h>
+
+int main() {
+  assert(__sanitizer_get_allocated_size(NULL) == 0);
+  assert(malloc_usable_size(NULL) == 0);
+
+  int size = 1234567;
+  void *p = malloc(size);
+  assert(__sanitizer_get_allocated_size(p) == size);
+  assert(malloc_usable_size(p) == size);
+  free(p);
+  return 0;
+}