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

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>

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 1c69476c8a09480ef71b0fecb7b16fe909521e1e..89579165ef4dc7de604318b2b3404b683264b497 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -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)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 35eebb5e77694a1b57112f374f04d4d99e00c287..662ad7312697094f1deed3a199668d83ba8728cf 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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;
                }