If BTF is corrupted DATASEC's variable type ID might be incorrect.
Prevent this easy to detect situation with extra NULL check.
Reported by oss-fuzz project.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211103173213.1376990-3-andrii@kernel.org