Re: [syzbot] [net?] KASAN: slab-use-after-free Write in l2tp_session_delete

Hillf Danton
2024-07-10T12:55:37Z

On 25/06/2024 14:25, syzbot wrote:
> syzbot found the following issue on:
>
> HEAD commit: 185d72112b95 net: xilinx: axienet: Enable multicast by def..
> git tree: net-next
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1062bd46980000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git 185d72112b95

--- x/net/l2tp/l2tp_core.c
+++ y/net/l2tp/l2tp_core.c
@@ -1290,17 +1290,20 @@ static void l2tp_session_unhash(struct l
static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel)
{
struct l2tp_session *session;
- struct list_head __rcu *pos;
- struct list_head *tmp;

spin_lock_bh(&tunnel->list_lock);
tunnel->acpt_newsess = false;
- list_for_each_safe(pos, tmp, &tunnel->session_list) {
- session = list_entry(pos, struct l2tp_session, list);
+ for (;;) {
+ session = list_first_entry_or_null(&tunnel->session_list,
+ struct l2tp_session, list);
+ if (!session)
+ break;
+ l2tp_session_inc_refcount(session);
list_del_init(&session->list);
spin_unlock_bh(&tunnel->list_lock);
l2tp_session_delete(session);
spin_lock_bh(&tunnel->list_lock);
+ l2tp_session_dec_refcount(session);
}
spin_unlock_bh(&tunnel->list_lock);
}
--