在 2026/4/28 02:43, [email protected] 写道: >> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c >> index 1e8754877dd1..51b6ea4bb8cb 100644 >> --- a/kernel/bpf/helpers.c >> +++ b/kernel/bpf/helpers.c >> @@ -2593,6 +2593,15 @@ __bpf_kfunc struct bpf_list_node >> *bpf_list_pop_back(struct bpf_list_head *head) >> return __bpf_list_del(head, h->prev); >> } >> >> +__bpf_kfunc struct bpf_list_node *bpf_list_del(struct bpf_list_head *head, >> + struct bpf_list_node *node) >> +{ >> + struct bpf_list_node_kern *kn = (void *)node; >> + >> + /* verifier guarantees node is a list node rather than list head */ >> + return __bpf_list_del(head, &kn->list_head); >> +} > > Can this kfunc actually be called from any BPF program? Looking at the > verifier's handling of KF_ARG_PTR_TO_LIST_NODE arguments in > check_kfunc_args(): > > case KF_ARG_PTR_TO_LIST_NODE: > if (reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) { > verbose(env, "%s expected pointer to allocated object\n", ...); > return -EINVAL; > } > if (!reg->ref_obj_id) { > verbose(env, "allocated object must be referenced\n"); > return -EINVAL; > } > > This code path unconditionally requires an owning reference (ref_obj_id > must be non-zero). > > However, once a node is added to the list via bpf_list_push_front/back, > the owning reference is converted to a non-owning reference > (ref_obj_id becomes 0) via ref_convert_owning_non_owning() and the > original owning reference is released. Any subsequent access to that > in-list node (including via bpf_list_front/back) only provides > non-owning references with ref_obj_id == 0. > > This means: > - Passing a non-owning ref to bpf_list_del() fails the verifier's > "!reg->ref_obj_id" check with "allocated object must be referenced" > - Passing an owning ref to a node not yet in the list passes the > verifier check, but __bpf_list_del() will return NULL because > node_kern->owner != head > > The sister kfunc bpf_rbtree_remove handles this by having a special > branch in check_kfunc_args() that accepts non-owning references for > that specific kfunc. Does bpf_list_del need similar handling?
I have already fixed this issue in [PATCH bpf-next v10 7/8]. > Looking at __bpf_list_del() in kernel/bpf/helpers.c: > > node = container_of(n, struct bpf_list_node_kern, list_head); > if (unlikely(READ_ONCE(node->owner) != head)) > return NULL; > > Emil Tsalapatis and the Sashiko review bot raised concerns about > removing the WARN_ON_ONCE that was in v8 of this series. The original > WARN_ON_ONCE helped detect list corruption by triggering a kernel > warning when owner != head. The current unlikely() check silently > returns NULL instead. > > Should this check trigger a warning for debugging list corruption issues? In previous discussions, people generally advised against keeping warnings on this kind of path that can be triggered by BPF programs. > Additionally, the Sashiko review noted a reuse bug: when > bpf_list_head_free() is called on a list that still contains elements, > those elements remain allocated but their owner field still points to > the now-freed head. Since the owner field is checked but never cleared, > could this lead to dangling pointer issues if nodes aren't freed > properly during list cleanup? I have already fixed this issue in [PATCH bpf-next v10 2/8]. >> @@ -4725,6 +4734,7 @@ BTF_ID_FLAGS(func, bpf_list_push_back, >> KF_IMPLICIT_ARGS) >> BTF_ID_FLAGS(func, bpf_list_push_back_impl) >> BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL) >> BTF_ID_FLAGS(func, bpf_list_pop_back, KF_ACQUIRE | KF_RET_NULL) >> +BTF_ID_FLAGS(func, bpf_list_del, KF_ACQUIRE | KF_RET_NULL) >> BTF_ID_FLAGS(func, bpf_list_front, KF_RET_NULL) >> BTF_ID_FLAGS(func, bpf_list_back, KF_RET_NULL) >> BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL) > > [ ... ] > > > --- > AI reviewed your patch. Please fix the bug or email reply why it's not a bug. > See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md > > CI run summary: https://github.com/kernel-patches/bpf/actions/runs/25009536772 -- Thanks Kaitao Cheng
