Fix get_groups interceptor in sanitizer

[marxin]

Summary

Hello.

As mentioned in the GCC bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80166

wrongly fails when size == 0 or when a negative number.

[kcc]

LGTM, thanks!

[marxin]

Can you please commit the patch as I don't have write access?

[kcc]

r299036.

Next time, please make your patches from llvm/projects/compiler-rt dir, not from llvm/projects

compiler-rt/lib/msan/tests/msan_test.cc

     EXPECT_NOT_POISONED(gids[i]);
 }
 
+TEST(MemorySanitizer, getgroups_zero) {
+  gid_t group;
+  int n = getgroups(0, &group);
+  ASSERT_GE(n, 0);
+}
+
+TEST(MemorySanitizer, getgroups_negative) {
+  gid_t group;
+  int n = getgroups(-1, 0);
+  ASSERT_EQ(-1, n);
+
+  n = getgroups(-1, 0);
+  ASSERT_EQ(-1, n);
+}
+
 TEST(MemorySanitizer, wordexp) {
   wordexp_t w;
   int res = wordexp("a b c", &w, 0);

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc

   // its metadata. See
   // https://github.com/google/sanitizers/issues/321.
   int res = REAL(getgroups)(size, lst);
-  if (res && lst) COMMON_INTERCEPTOR_WRITE_RANGE(ctx, lst, res * sizeof(*lst));
+  if (res >= 0 && lst && size > 0)
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, lst, res * sizeof(*lst));
   return res;
 }
 #define INIT_GETGROUPS COMMON_INTERCEPT_FUNCTION(getgroups);