netdev - Re: [PATCH bpf] bpf: fix NULL deref in btf_type_is_resolve_source

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Date:   Wed, 19 Jun 2019 12:08:07 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH bpf] bpf: fix NULL deref in btf_type_is_resolve_source_only

On Wed, Jun 19, 2019 at 12:01 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> Commit 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec")
> added invocations of btf_type_is_resolve_source_only before
> btf_type_nosize_or_null which checks for the NULL pointer.
> Swap the order of btf_type_nosize_or_null and
> btf_type_is_resolve_source_only to make sure the do the NULL pointer
> check first.
>
> Fixes: 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  kernel/bpf/btf.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index cad09858a5f2..546ebee39e2a 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -1928,8 +1928,8 @@ static int btf_array_resolve(struct btf_verifier_env *env,
>         /* Check array->index_type */
>         index_type_id = array->index_type;
>         index_type = btf_type_by_id(btf, index_type_id);
> -       if (btf_type_is_resolve_source_only(index_type) ||
> -           btf_type_nosize_or_null(index_type)) {
> +       if (btf_type_nosize_or_null(index_type) ||
> +           btf_type_is_resolve_source_only(index_type)) {
>                 btf_verifier_log_type(env, v->t, "Invalid index");
>                 return -EINVAL;
>         }
> @@ -1948,8 +1948,8 @@ static int btf_array_resolve(struct btf_verifier_env *env,
>         /* Check array->type */
>         elem_type_id = array->type;
>         elem_type = btf_type_by_id(btf, elem_type_id);
> -       if (btf_type_is_resolve_source_only(elem_type) ||
> -           btf_type_nosize_or_null(elem_type)) {
> +       if (btf_type_nosize_or_null(elem_type) ||
> +           btf_type_is_resolve_source_only(elem_type)) {
>                 btf_verifier_log_type(env, v->t,
>                                       "Invalid elem");
>                 return -EINVAL;
> @@ -2170,8 +2170,8 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
>                 const struct btf_type *member_type = btf_type_by_id(env->btf,
>                                                                 member_type_id);
>
> -               if (btf_type_is_resolve_source_only(member_type) ||
> -                   btf_type_nosize_or_null(member_type)) {
> +               if (btf_type_nosize_or_null(member_type) ||
> +                   btf_type_is_resolve_source_only(member_type)) {
>                         btf_verifier_log_member(env, v->t, member,
>                                                 "Invalid member");
>                         return -EINVAL;
> --
> 2.22.0.410.gd8fdbe21b5-goog
>