What is guaranteed when realloc(owner, larger_size) returns NULL for a nonzero valid size?

What is guaranteed when realloc(owner, larger_size) returns NULL for a nonzero valid size?

1. The old allocation remains valid and unchanged.
2. The old allocation has already been freed.
3. The first half of the old allocation remains valid.
4. The caller must free the NULL result before reusing owner.