From 47186409c092cd7dd70350999186c700233e854d Mon Sep 17 00:00:00 2001 From: Runyu Xiao Date: Thu, 11 Jun 2026 13:35:43 +0800 Subject: [PATCH] kcm: use WRITE_ONCE() when changing lower socket callbacks kcm_attach() replaces a live lower TCP socket's sk_data_ready and sk_write_space callbacks with KCM handlers, and kcm_unattach() restores them later. Those callback-pointer updates are still plain stores even though the same fields can be read and invoked concurrently on other CPUs. If another CPU observes an older callback snapshot after the live field has already been restored, callback execution can run with a mismatched target and sk_user_data state, leading to stale or misdirected wakeups. Use WRITE_ONCE() for the callback replacement and restore operations so these shared callback fields follow the same visibility contract already established by the earlier 4022 fixes. Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Signed-off-by: Runyu Xiao Link: https://patch.msgid.link/20260611053543.2429462-1-runyu.xiao@seu.edu.cn Signed-off-by: Paolo Abeni --- net/kcm/kcmsock.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index 3912e75079f5..a998336840c3 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -1304,8 +1304,8 @@ static int kcm_attach(struct socket *sock, struct socket *csock, psock->save_write_space = csk->sk_write_space; psock->save_state_change = csk->sk_state_change; csk->sk_user_data = psock; - csk->sk_data_ready = psock_data_ready; - csk->sk_write_space = psock_write_space; + WRITE_ONCE(csk->sk_data_ready, psock_data_ready); + WRITE_ONCE(csk->sk_write_space, psock_write_space); csk->sk_state_change = psock_state_change; write_unlock_bh(&csk->sk_callback_lock); @@ -1381,8 +1381,8 @@ static void kcm_unattach(struct kcm_psock *psock) */ write_lock_bh(&csk->sk_callback_lock); csk->sk_user_data = NULL; - csk->sk_data_ready = psock->save_data_ready; - csk->sk_write_space = psock->save_write_space; + WRITE_ONCE(csk->sk_data_ready, psock->save_data_ready); + WRITE_ONCE(csk->sk_write_space, psock->save_write_space); csk->sk_state_change = psock->save_state_change; strp_stop(&psock->strp);