Re: [PATCH net v2] tcp: clear sock_ops cb flags before force-closing a child socket

[Kuniyuki Iwashima]

On Wed, Jun 10, 2026 at 9:00 AM Sechang Lim <rhkrqnwk98@xxxxxxxxx> wrote:
>
> A child socket inherits the listener's bpf_sock_ops_cb_flags via
> sk_clone_lock(). If its setup fails in tcp_v4_syn_recv_sock() /
> tcp_v6_syn_recv_sock(), the child is freed through put_and_exit, where
> inet_csk_prepare_forced_close() drops the socket lock and tcp_done() runs
> without it.
>
> If BPF_SOCK_OPS_STATE_CB_FLAG was inherited, tcp_done() -> tcp_set_state()
> calls tcp_call_bpf(), which expects the lock and trips sock_owned_by_me():
>
>   WARNING: include/net/sock.h:1799 at tcp_set_state+0x433/0x550
>   RIP: 0010:tcp_set_state+0x433/0x550 include/net/sock.h:1799
>   Call Trace:
>    <IRQ>
>    tcp_done+0xba/0x250 net/ipv4/tcp.c:5095
>    tcp_v4_syn_recv_sock+0x850/0xa50 net/ipv4/tcp_ipv4.c:1787
>    tcp_check_req+0xf30/0x1360 net/ipv4/tcp_minisocks.c:926
>    tcp_v4_rcv+0x1047/0x1b50 net/ipv4/tcp_ipv4.c:2164
>    </IRQ>
>
> The child is freed before it is ever established, so it should run no
> sock_ops callback. Clear its cb flags in inet_csk_prepare_forced_close(),
> which covers all forced-close callers.
>
> Suggested-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> Fixes: d44874910a26 ("bpf: Add BPF_SOCK_OPS_STATE_CB")
> Signed-off-by: Sechang Lim <rhkrqnwk98@xxxxxxxxx>
> ---
> v2:
>  - move the clearing into inet_csk_prepare_forced_close() (Jiayuan Chen,
>    Simon Horman)
>
> v1:
>  - https://lore.kernel.org/all/20260605094954.1374489-1-rhkrqnwk98@xxxxxxxxx/
>
>  include/net/tcp.h               | 7 +++++++
>  net/ipv4/inet_connection_sock.c | 1 +
>  2 files changed, 8 insertions(+)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 98848db62894..97eac5fa341c 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2942,6 +2942,11 @@ static inline int tcp_call_bpf_3arg(struct sock *sk, int op, u32 arg1, u32 arg2,
>         return tcp_call_bpf(sk, op, 3, args);
>  }
>
> +static inline void tcp_clear_sock_ops_cb_flags(struct sock *sk)
> +{
> +       tcp_sk(sk)->bpf_sock_ops_cb_flags = 0;
> +}
> +
>  #else
>  static inline int tcp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args)
>  {
> @@ -2959,6 +2964,8 @@ static inline int tcp_call_bpf_3arg(struct sock *sk, int op, u32 arg1, u32 arg2,
>         return -EPERM;
>  }
>
> +static inline void tcp_clear_sock_ops_cb_flags(struct sock *sk) {}

nit: I think prefered style is

static inline void tcp_clear_sock_ops_cb_flags(struct sock *sk)
{
}

> +
>  #endif
>
>  static inline u32 tcp_timeout_init(struct sock *sk)
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index dbcd37dfdc15..209f73a61a1d 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1290,6 +1290,7 @@ void inet_csk_prepare_forced_close(struct sock *sk)
>         __releases(&sk->sk_lock.slock)
>  {
>         /* sk_clone_lock locked the socket and set refcnt to 2 */
> +       tcp_clear_sock_ops_cb_flags(sk);

mptcp's ->syn_recv_sock() will trigger the hook in the failure path.

inet_csk_prepare_for_destroy_sock() is a better fit.  We don't
care if the child socket is locked in this path.


>         bh_unlock_sock(sk);
>         sock_put(sk);
>         inet_csk_prepare_for_destroy_sock(sk);
> --
> 2.43.0
>