From: Kaitao Cheng <[email protected]> Refactor __bpf_list_add to accept (node, head, struct list_head **prev_ptr, ..) instead of (node, head, bool tail, ..). Load prev from *prev_ptr after INIT_LIST_HEAD(h), so we never dereference an uninitialized h->prev when head was 0-initialized (e.g. push_back passes &h->prev).
When prev is not the list head, validate that prev is in the list via its owner. Prepares for bpf_list_add_impl(head, new, prev, ..) to insert after a given list node. Signed-off-by: Kaitao Cheng <[email protected]> --- kernel/bpf/helpers.c | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 6dddb2377047..669e380746a6 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2386,9 +2386,11 @@ __bpf_kfunc void *bpf_refcount_acquire_impl(void *p__refcounted_kptr, void *meta static int __bpf_list_add(struct bpf_list_node_kern *node, struct bpf_list_head *head, - bool tail, struct btf_record *rec, u64 off) + struct list_head **prev_ptr, + struct btf_record *rec, u64 off) { struct list_head *n = &node->list_head, *h = (void *)head; + struct list_head *prev; /* If list_head was 0-initialized by map, bpf_obj_init_field wasn't * called on its fields, so init here @@ -2396,19 +2398,31 @@ static int __bpf_list_add(struct bpf_list_node_kern *node, if (unlikely(!h->next)) INIT_LIST_HEAD(h); + prev = *prev_ptr; + + /* When prev is not the list head, it must be a node in this list. */ + if (prev != h) { + struct bpf_list_node_kern *prev_kn = + container_of(prev, struct bpf_list_node_kern, list_head); + + if (unlikely(READ_ONCE(prev_kn->owner) != head)) + goto fail; + } + /* node->owner != NULL implies !list_empty(n), no need to separately * check the latter */ - if (cmpxchg(&node->owner, NULL, BPF_PTR_POISON)) { - /* Only called from BPF prog, no need to migrate_disable */ - __bpf_obj_drop_impl((void *)n - off, rec, false); - return -EINVAL; - } + if (cmpxchg(&node->owner, NULL, BPF_PTR_POISON)) + goto fail; - tail ? list_add_tail(n, h) : list_add(n, h); + list_add(n, prev); WRITE_ONCE(node->owner, head); - return 0; + +fail: + /* Only called from BPF prog, no need to migrate_disable */ + __bpf_obj_drop_impl((void *)n - off, rec, false); + return -EINVAL; } __bpf_kfunc int bpf_list_push_front_impl(struct bpf_list_head *head, @@ -2417,8 +2431,9 @@ __bpf_kfunc int bpf_list_push_front_impl(struct bpf_list_head *head, { struct bpf_list_node_kern *n = (void *)node; struct btf_struct_meta *meta = meta__ign; + struct list_head *h = (void *)head; - return __bpf_list_add(n, head, false, meta ? meta->record : NULL, off); + return __bpf_list_add(n, head, &h, meta ? meta->record : NULL, off); } __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head, @@ -2427,8 +2442,9 @@ __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head, { struct bpf_list_node_kern *n = (void *)node; struct btf_struct_meta *meta = meta__ign; + struct list_head *h = (void *)head; - return __bpf_list_add(n, head, true, meta ? meta->record : NULL, off); + return __bpf_list_add(n, head, &h->prev, meta ? meta->record : NULL, off); } static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head, -- 2.50.1 (Apple Git-155)
