From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 369C9629 for ; Wed, 2 Nov 2022 03:29:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4077BC433D6; Wed, 2 Nov 2022 03:29:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1667359744; bh=zBfkaFvI5JWSbghU23CyT0em6cHrhP1RFQ2l0rr1BXw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AaVTinkhqw5OaZHWDLQPXX9xR3k0JT96Ir2mr2K3z0quUrjAyJSMwcHB7tuKTtk6+ dx2RZ9JjclQajnkdCC4Pk8UbKKF325oRaewBRuKzdsn2yDtd96k9OPAAk4kUY1cbKg YM6kiBvakAx8d1U/C3d3LdhefNdQY0KEFPB4vc6I= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Steven Rostedt (Google)" , Guenter Roeck , Takashi Iwai Subject: [PATCH 4.19 27/78] ALSA: Use del_timer_sync() before freeing timer Date: Wed, 2 Nov 2022 03:34:12 +0100 Message-Id: <20221102022053.797366716@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221102022052.895556444@linuxfoundation.org> References: <20221102022052.895556444@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Steven Rostedt (Google) 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 --- sound/synth/emux/emux.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) --- a/sound/synth/emux/emux.c +++ b/sound/synth/emux/emux.c @@ -138,15 +138,10 @@ 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);