bpf: Explicitly size compatible_reg_types

Arrays with designated initializers have an implicit length of the highest initialized value plus one. I used this to ensure that newly added entries in enum bpf_reg_type get a NULL entry in compatible_reg_types. This is difficult to understand since it requires knowledge of the peculiarities of designated initializers. Use __BPF_ARG_TYPE_MAX to size the array instead. Suggested-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/20200923160156.80814-1-lmb@cloudflare.com

Author: lmb

kernel/bpf/verifier.c

@@ -4002,7 +4002,7 @@ static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_T
 static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
 static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
 
-static const struct bpf_reg_types *compatible_reg_types[] = {
+static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 [ARG_PTR_TO_MAP_KEY]= &map_key_value_types,
 [ARG_PTR_TO_MAP_VALUE]= &map_key_value_types,
 [ARG_PTR_TO_UNINIT_MAP_VALUE]= &map_key_value_types,
@@ -4025,7 +4025,6 @@ static const struct bpf_reg_types *compatible_reg_types[] = {
 [ARG_PTR_TO_ALLOC_MEM_OR_NULL]= &alloc_mem_types,
 [ARG_PTR_TO_INT]= &int_ptr_types,
 [ARG_PTR_TO_LONG]= &int_ptr_types,
-[__BPF_ARG_TYPE_MAX]= NULL,
 };
 
 static int check_reg_type(struct bpf_verifier_env *env, u32 regno,