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

On Wed, Jun 10, 2026 at 11:11:49PM -0700, Kuniyuki Iwashima wrote:

On Wed, Jun 10, 2026 at 9:00 AM Sechang Lim [off-list ref] wrote:

quoted

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@linux.dev>
Fixes: d44874910a26 ("bpf: Add BPF_SOCK_OPS_STATE_CB")
Signed-off-by: Sechang Lim <redacted>
---
v2:
 - move the clearing into inet_csk_prepare_forced_close() (Jiayuan Chen,
   Simon Horman)

v1:
 - https://lore.kernel.org/all/20260605094954.1374489-1-rhkrqnwk98@gmail.com/ (local)

 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)
{
}

Will fix in v3.

quoted

+
 #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.

Makes sense, I missed the mptcp failure path. Moving it there in v3.

Thanks,
Sechang