On Wed, Jun 28, 2023 at 7:52 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> Per discussion with Alexei, the PTR_UNTRUSTED flag should not been
> cleared when we start to walk a new struct, because the struct in
> question may be a struct nested in a union. We should also check and set
> this flag before we walk its each member, in case itself is a union.
>
> Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> kernel/bpf/btf.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 29fe21099298..e0a493230727 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6133,7 +6133,6 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
> const char *tname, *mname, *tag_value;
> u32 vlen, elem_id, mid;
>
> - *flag = 0;
> again:
> tname = __btf_name_by_offset(btf, t->name_off);
> if (!btf_type_is_struct(t)) {
> @@ -6142,6 +6141,14 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
> }
>
> vlen = btf_type_vlen(t);
> + if (BTF_INFO_KIND(t->info) == BTF_KIND_UNION && vlen != 1)
> + /*
> + * walking unions yields untrusted pointers
> + * with exception of __bpf_md_ptr and other
> + * unions with a single member
> + */
> + *flag |= PTR_UNTRUSTED;
> +
> if (off + size > t->size) {
> /* If the last element is a variable size array, we may
> * need to relax the rule.
> @@ -6302,15 +6309,6 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
> * of this field or inside of this struct
> */
> if (btf_type_is_struct(mtype)) {
> - if (BTF_INFO_KIND(mtype->info) == BTF_KIND_UNION &&
> - btf_type_vlen(mtype) != 1)
> - /*
> - * walking unions yields untrusted pointers
> - * with exception of __bpf_md_ptr and other
> - * unions with a single member
> - */
> - *flag |= PTR_UNTRUSTED;
> -
> /* our field must be inside that union or struct */
> t = mtype;
>
> @@ -6476,7 +6474,7 @@ bool btf_struct_ids_match(struct bpf_verifier_log *log,
> bool strict)
> {
> const struct btf_type *type;
> - enum bpf_type_flag flag;
> + enum bpf_type_flag flag = 0;
> int err;
>
> /* Are we already done? */
> --
> 2.39.3
>
Just noticed that it breaks test_sk_storage_tracing, because skb->sk
is in a union:
struct sk_buff {
...
union {
struct sock *sk;
int ip_defrag_offset;
};
...
};
I will think about it.
--
Regards
Yafang
