In the Linux kernel, the following vulnerability has been resolved: tcp: Fix refcnt handling in __inet_hash_connect(). syzbot reported a warning in sk_nulls_del_node_init_rcu(). The commit 66b60b0c8c4a ("dccp/tcp: Unhash sk from ehash for tb2 alloc failure after check_estalblished().") tried to fix an issue that an unconnected socket occupies an ehash entry when bhash2 allocation fails. In such a case, we need to revert changes done by check_established(), which does not hold refcnt when inserting socket into ehash. So, to revert the change, we need to __sk_nulls_add_node_rcu() instead of sk_nulls_add_node_rcu(). Otherwise, sock_put() will cause refcnt underflow and leak the socket. [0]: WARNING: CPU: 0 PID: 23948 at include/net/sock.h:799 sk_nulls_del_node_init_rcu+0x166/0x1a0 include/net/sock.h:799 Modules linked in: CPU: 0 PID: 23948 Comm: syz-executor.2 Not tainted 6.8.0-rc6-syzkaller-00159-gc055fc00c07b #0 Hardware name: Google Google Compute Engine/Google Compute Engine, …