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In-Reply-To: <20260304031606.43884-2-pilgrimtao@gmail.com> References: <20260304031606.43884-1-pilgrimtao@gmail.com> <20260304031606.43884-2-pilgrimtao@gmail.com> Date: Wed, 04 Mar 2026 15:50:26 +0000 Message-ID: <87wlzry4ot.fsf@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Chengkaitao writes: > From: Kaitao Cheng > > If a user holds ownership of a node in the middle of a list, they > can directly remove it from the list without strictly adhering to > deletion rules from the head or tail. > > This is typically paired with bpf_refcount. After calling > bpf_list_del, it is generally necessary to drop the reference to > the list node twice to prevent reference count leaks. > > Signed-off-by: Kaitao Cheng > --- > kernel/bpf/helpers.c | 19 +++++++++++++++++++ > kernel/bpf/verifier.c | 6 +++++- > 2 files changed, 24 insertions(+), 1 deletion(-) > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index 6eb6c82ed2ee..19d88da8e694 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -2459,6 +2459,24 @@ __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head) > return __bpf_list_del(head, true); > } > > +__bpf_kfunc struct bpf_list_node *bpf_list_del(struct bpf_list_head *head, > + struct bpf_list_node *node) > +{ > + struct bpf_list_node_kern *knode = (struct bpf_list_node_kern *)node; > + struct list_head *h = (void *)head; > + > + if (unlikely(!knode)) Can you pass knode==NULL to this kfunc? > + return NULL; > + > + if (WARN_ON_ONCE(READ_ONCE(knode->owner) != h)) it looks like you can just do READ_ONCE(knode->owner) != head. owner is void*, what's the point of defining struct list_head *h? > + return NULL; > + > + list_del_init(&knode->list_head); > + WRITE_ONCE(knode->owner, NULL); > + > + return node; > +} > + > __bpf_kfunc struct bpf_list_node *bpf_list_front(struct bpf_list_head *head) > { > struct list_head *h = (struct list_head *)head; > @@ -4545,6 +4563,7 @@ BTF_ID_FLAGS(func, bpf_list_push_front_impl) > 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) > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 67c09b43a497..c9557d3fb8dd 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -12461,6 +12461,7 @@ enum special_kfunc_type { > KF_bpf_list_push_back_impl, > KF_bpf_list_pop_front, > KF_bpf_list_pop_back, > + KF_bpf_list_del, > KF_bpf_list_front, > KF_bpf_list_back, > KF_bpf_cast_to_kern_ctx, > @@ -12521,6 +12522,7 @@ BTF_ID(func, bpf_list_push_front_impl) > BTF_ID(func, bpf_list_push_back_impl) > BTF_ID(func, bpf_list_pop_front) > BTF_ID(func, bpf_list_pop_back) > +BTF_ID(func, bpf_list_del) > BTF_ID(func, bpf_list_front) > BTF_ID(func, bpf_list_back) > BTF_ID(func, bpf_cast_to_kern_ctx) > @@ -12996,6 +12998,7 @@ static bool is_bpf_list_api_kfunc(u32 btf_id) > btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] || > btf_id == special_kfunc_list[KF_bpf_list_pop_front] || > btf_id == special_kfunc_list[KF_bpf_list_pop_back] || > + btf_id == special_kfunc_list[KF_bpf_list_del] || > btf_id == special_kfunc_list[KF_bpf_list_front] || > btf_id == special_kfunc_list[KF_bpf_list_back]; > } > @@ -13118,7 +13121,8 @@ static bool check_kfunc_is_graph_node_api(struct bpf_verifier_env *env, > switch (node_field_type) { > case BPF_LIST_NODE: > ret = (kfunc_btf_id == special_kfunc_list[KF_bpf_list_push_front_impl] || > - kfunc_btf_id == special_kfunc_list[KF_bpf_list_push_back_impl]); > + kfunc_btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] || > + kfunc_btf_id == special_kfunc_list[KF_bpf_list_del]); > break; > case BPF_RB_NODE: > ret = (kfunc_btf_id == special_kfunc_list[KF_bpf_rbtree_remove] || > -- > 2.50.1 (Apple Git-155)