bpf: allow non-owning list-node args via __nonown_allowed

KF_ARG_PTR_TO_LIST_NODE normally requires an owning reference
(PTR_TO_BTF_ID | MEM_ALLOC with ref_obj_id). Introduce  the
__nonown_allowed annotation on selected list-node arguments so
non-owning references with ref_obj_id==0 are accepted as well.

This patch only adds the generic verifier support and documents the
annotation. Later patches in the series will apply it to bpf_list_add
/del(), and bpf_list_is_first/last(), allowing bpf_list_front/back()
results to be used as the insertion point, deletion target, or query
target for those kfuncs.

Verifier keeps existing owning-ref checks by default; only arguments
annotated with __nonown_allowed bypass MEM_ALLOC/ref_obj_id checks
and then follow the same list-node validation path.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260521032306.97118-4-kaitao.cheng@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

0 files changed, 0 insertions, 0 deletions