[asan] Don't crash on fclose(NULL)

[kubamracek]

Summary

It's explicitly forbidden to call fclose with NULL, but at least on Darwin, this succeeds and doesn't segfault. To maintain binary compatibility, ASan should survice fclose(NULL) as well.

lib/sanitizer_common/sanitizer_common_interceptors.inc

UNUSED static void SetInterceptorMetadata(__sanitizer_FILE *addr,
   h->file = file;
 }
 
 UNUSED static const FileMetadata *GetInterceptorMetadata(
     __sanitizer_FILE *addr) {
   MetadataHashMap::Handle h(interceptor_metadata_map, (uptr)addr,
                             /* remove */ false,
                             /* create */ false);
-  if (h.exists()) {
+  if (addr && h.exists()) {
     CHECK(!h.created());
     CHECK(h->type == CommonInterceptorMetadata::CIMT_FILE);
     return &h->file;
   } else {
     return 0;
   }
 }
 

test/asan/TestCases/Darwin/fclose.c

+// RUN: %clang_asan %s -o %t
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, const char * argv[]) {
+  fclose(NULL);
+  fprintf(stderr, "Finished.\n");
+  return 0;
+}
+
+// CHECK: Finished.