On Mon, 2024-05-20 at 13:40 -0700, Kui-Feng Lee wrote:
> The verifier has field information for specific special types, such as
> kptr, rbtree root, and list head. These types are handled
> differently. However, we did not previously examine the types of fields of
> a struct type variable. Field information records were not generated for
> the kptrs, rbtree roots, and linked_list heads that are not located at the
> outermost struct type of a variable.
>
> For example,
>
> struct A {
> struct task_struct __kptr * task;
> };
>
> struct B {
> struct A mem_a;
> }
>
> struct B var_b;
>
> It did not examine "struct A" so as not to generate field information for
> the kptr in "struct A" for "var_b".
>
> This patch enables BPF programs to define fields of these special types in
> a struct type other than the direct type of a variable or in a struct type
> that is the type of a field in the value type of a map.
>
> Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
> ---
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
[...]
> + /* Look into variables of struct types */
> + if ((field_type == BPF_KPTR_REF || !field_type) &&
> + __btf_type_is_struct(var_type)) {
This code would have looked nicer (handled inside the same switch as
all other branches) if we had BPF_NESTED_FIELD in `btf_field_type` or
something like that. But that's probably be an overkill.
> + sz = var_type->size;
> + if (expected_size && expected_size != sz * nelems)
> + return 0;
> + ret = btf_find_nested_struct(btf, var_type, off, nelems, field_mask,
> + &info[0], info_cnt);
> + return ret;
> + }
[...]
