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bpf: Add bpf_list_add to insert node after a given list node

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Add a new kfunc bpf_list_add(head, new, prev, meta, off) that
inserts 'new' after 'prev' in the BPF linked list. Both must be in
the same list; 'prev' must already be in the list. The new node must
be an owning reference (e.g. from bpf_obj_new); the kfunc consumes
that reference and the node becomes non-owning once inserted.

We have added an additional parameter bpf_list_head *head to
bpf_list_add, as the verifier requires the head parameter to
check whether the lock is being held.

Returns 0 on success, -EINVAL if 'prev' is not in a list or 'new'
is already in a list (or duplicate insertion). On failure, the
kernel drops the passed-in node.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260521032306.97118-7-kaitao.cheng@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kaitao Cheng 2026-05-21 11:23:04 +08:00 committed by Alexei Starovoitov
parent e6919ff67c
commit a3493ca504
2 changed files with 20 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
kernel/bpf/helpers.c
View File

@ -2577,6 +2577,16 @@ __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
return bpf_list_push_back(head, node, meta__ign, off);
}
__bpf_kfunc int bpf_list_add(struct bpf_list_head *head, struct bpf_list_node *new,
struct bpf_list_node *prev__nonown_allowed,
struct btf_struct_meta *meta, u64 off)
{
struct bpf_list_node_kern *n = (void *)new, *p = (void *)prev__nonown_allowed;
struct list_head *prev_ptr = &p->list_head;
return __bpf_list_add(n, head, &prev_ptr, meta ? meta->record : NULL, off);
}
static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head,
struct list_head *n)
{
@ -4756,6 +4766,7 @@ BTF_ID_FLAGS(func, bpf_list_push_front, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, bpf_list_push_front_impl)
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_add, KF_IMPLICIT_ARGS)
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)

12
kernel/bpf/verifier.c
View File

@ -10959,6 +10959,7 @@ enum special_kfunc_type {
KF_bpf_list_push_front,
KF_bpf_list_push_back_impl,
KF_bpf_list_push_back,
KF_bpf_list_add,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
KF_bpf_list_del,
@ -11028,6 +11029,7 @@ BTF_ID(func, bpf_list_push_front_impl)
BTF_ID(func, bpf_list_push_front)
BTF_ID(func, bpf_list_push_back_impl)
BTF_ID(func, bpf_list_push_back)
BTF_ID(func, bpf_list_add)
BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
BTF_ID(func, bpf_list_del)
@ -11140,7 +11142,8 @@ static bool is_bpf_list_push_kfunc(u32 func_id)
return func_id == special_kfunc_list[KF_bpf_list_push_front] ||
func_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||
func_id == special_kfunc_list[KF_bpf_list_push_back] ||
func_id == special_kfunc_list[KF_bpf_list_push_back_impl];
func_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
func_id == special_kfunc_list[KF_bpf_list_add];
}
static bool is_bpf_rbtree_add_kfunc(u32 func_id)
@ -19524,8 +19527,11 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
int struct_meta_reg = BPF_REG_3;
int node_offset_reg = BPF_REG_4;
/* rbtree_add has extra 'less' arg, so args-to-fixup are in diff regs */
if (is_bpf_rbtree_add_kfunc(desc->func_id)) {
/* list_add/rbtree_add have an extra arg (prev/less),
* so args-to-fixup are in diff regs.
*/
if (desc->func_id == special_kfunc_list[KF_bpf_list_add] ||
is_bpf_rbtree_add_kfunc(desc->func_id)) {
struct_meta_reg = BPF_REG_4;
node_offset_reg = BPF_REG_5;
}