From: Takashi Iwai Date: Mon, 20 Apr 2026 06:17:20 +0000 (+0200) Subject: ALSA: core: Fix potential data race at fasync handling X-Git-Tag: v7.1-rc1~22^2~10 X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=8146cd333d235ed32d48bb803fdf743472d7c783;p=thirdparty%2Fkernel%2Flinux.git ALSA: core: Fix potential data race at fasync handling In snd_fasync_work_fn(), which is the offload work for traversing and processing the pending fasync list, the call of kill_fasync() is done outside the snd_fasync_lock for avoiding deadlocks. The problem is that its the references of fasync->on, fasync->signal and fasync->poll are done there also outside the lock. Since these may be modified by snd_kill_fasync() call concurrently from other process, inconsistent values might be passed to kill_fasync(). Although there shouldn't be critical UAF, it's still better to be addressed. This patch moves the kill_fasync() argument evaluations inside the snd_fasync_lock for avoiding the data races above. The handling in fasync->on flag is optimized in the loop to skip directly. Also, for more clarity, snd_fasync_free() takes the lock and unlink the pending entry more directly instead of clearing fasync->on flag. Reported-by: Jake Lamberson Fixes: ef34a0ae7a26 ("ALSA: core: Add async signal helpers") Cc: Link: https://patch.msgid.link/20260420061721.3253644-1-tiwai@suse.de Signed-off-by: Takashi Iwai --- diff --git a/sound/core/misc.c b/sound/core/misc.c index 88d9e1f9a6e9..5aca09edf971 100644 --- a/sound/core/misc.c +++ b/sound/core/misc.c @@ -100,14 +100,18 @@ static LIST_HEAD(snd_fasync_list); static void snd_fasync_work_fn(struct work_struct *work) { struct snd_fasync *fasync; + int signal, poll; spin_lock_irq(&snd_fasync_lock); while (!list_empty(&snd_fasync_list)) { fasync = list_first_entry(&snd_fasync_list, struct snd_fasync, list); list_del_init(&fasync->list); + if (!fasync->on) + continue; + signal = fasync->signal; + poll = fasync->poll; spin_unlock_irq(&snd_fasync_lock); - if (fasync->on) - kill_fasync(&fasync->fasync, fasync->signal, fasync->poll); + kill_fasync(&fasync->fasync, signal, poll); spin_lock_irq(&snd_fasync_lock); } spin_unlock_irq(&snd_fasync_lock); @@ -158,7 +162,10 @@ void snd_fasync_free(struct snd_fasync *fasync) { if (!fasync) return; - fasync->on = 0; + + scoped_guard(spinlock_irq, &snd_fasync_lock) + list_del_init(&fasync->list); + flush_work(&snd_fasync_work); kfree(fasync); }