From: Steven Rostedt (Google) Date: Thu, 27 Oct 2022 03:12:36 +0000 (-0400) Subject: ALSA: Use del_timer_sync() before freeing timer X-Git-Tag: v5.15.79~405 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=259cb4dee1bb436dbe99270eaabfa714d66c328c;p=platform%2Fkernel%2Flinux-rpi.git ALSA: Use del_timer_sync() before freeing timer commit f0a868788fcbf63cdab51f5adcf73b271ede8164 upstream. The current code for freeing the emux timer is extremely dangerous: CPU0 CPU1 ---- ---- snd_emux_timer_callback() snd_emux_free() spin_lock(&emu->voice_lock) del_timer(&emu->tlist); <-- returns immediately spin_unlock(&emu->voice_lock); [..] kfree(emu); spin_lock(&emu->voice_lock); [BOOM!] Instead just use del_timer_sync() which will wait for the timer to finish before continuing. No need to check if the timer is active or not when doing so. This doesn't fix the race of a possible re-arming of the timer, but at least it won't use the data that has just been freed. [ Fixed unused variable warning by tiwai ] Cc: stable@vger.kernel.org Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Steven Rostedt (Google) Reviewed-by: Guenter Roeck Link: https://lore.kernel.org/r/20221026231236.6834b551@gandalf.local.home Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- diff --git a/sound/synth/emux/emux.c b/sound/synth/emux/emux.c index 5ed8e36..a870759 100644 --- a/sound/synth/emux/emux.c +++ b/sound/synth/emux/emux.c @@ -126,15 +126,10 @@ EXPORT_SYMBOL(snd_emux_register); */ int snd_emux_free(struct snd_emux *emu) { - unsigned long flags; - if (! emu) return -EINVAL; - spin_lock_irqsave(&emu->voice_lock, flags); - if (emu->timer_active) - del_timer(&emu->tlist); - spin_unlock_irqrestore(&emu->voice_lock, flags); + del_timer_sync(&emu->tlist); snd_emux_proc_free(emu); snd_emux_delete_virmidi(emu);