From 5337213381df578058e2e41da93cbd0e4639935f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?C=C3=A1ssio=20Gabriel?= Date: Wed, 6 May 2026 00:34:47 -0300 Subject: [PATCH] ALSA: core: Serialize deferred fasync state checks MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit snd_fasync_helper() updates fasync->on under snd_fasync_lock, and snd_fasync_work_fn() now also evaluates fasync->on under the same lock. snd_kill_fasync() still tests the flag before taking the lock, leaving an unsynchronized read against FASYNC enable/disable updates. Move the enabled-state check into the locked section. Also clear fasync->on under snd_fasync_lock in snd_fasync_free() before unlinking the pending entry. Together with the locked sender-side check, this publishes teardown before flushing the deferred work and prevents a racing sender from requeueing the entry after free has started. Fixes: ef34a0ae7a26 ("ALSA: core: Add async signal helpers") Fixes: 8146cd333d23 ("ALSA: core: Fix potential data race at fasync handling") Cc: stable@vger.kernel.org Signed-off-by: Cássio Gabriel Link: https://patch.msgid.link/20260506-alsa-core-fasync-on-lock-v1-1-ea48c77d6ca4@gmail.com Signed-off-by: Takashi Iwai --- sound/core/misc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/sound/core/misc.c b/sound/core/misc.c index 5aca09edf971..833124c8e4fa 100644 --- a/sound/core/misc.c +++ b/sound/core/misc.c @@ -148,9 +148,11 @@ EXPORT_SYMBOL_GPL(snd_fasync_helper); void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll) { - if (!fasync || !fasync->on) + if (!fasync) return; guard(spinlock_irqsave)(&snd_fasync_lock); + if (!fasync->on) + return; fasync->signal = signal; fasync->poll = poll; list_move(&fasync->list, &snd_fasync_list); @@ -163,8 +165,10 @@ void snd_fasync_free(struct snd_fasync *fasync) if (!fasync) return; - scoped_guard(spinlock_irq, &snd_fasync_lock) + scoped_guard(spinlock_irq, &snd_fasync_lock) { + fasync->on = 0; list_del_init(&fasync->list); + } flush_work(&snd_fasync_work); kfree(fasync);