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 4D7BA3D6484; Mon, 4 May 2026 14:19:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777904347; cv=none; b=H2BrmrBzC+x9q/SJWXUrlqU6VJe6k5mD3xJaJ9vch+6LbCqvbu8aKkNURHT97Ogq2EVos6+dkh21P9ecjbU5L0EPidWjuiQjXkckeI37pesRMGU2ziKRmJ0btoN/I2YPi06XWwOJPumP3/1iQwdBp0+aoPWk8X6T9FIrZSpR3qc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777904347; c=relaxed/simple; bh=t46b3yJOP5936Uj8m4r4LoRvvYzgQGm0EMYJgTWBrWE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=JhyvVVm+YyLUSb9D8DRcoS9y2xcMWDznlDV+M5SqczY8IFGbM2GOtxBR50vzyS3jmYMLE0D51XhxDyj1kqrTxDH/doVD/kbzmGGla4LijIfvokGhUqDIZi92ZblfgSvz4enW6IXZZ2H2qwBNSNBGyNplaN9jIi4brh7TNX0S/6g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=tOKliuhU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="tOKliuhU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD2FEC2BCC4; Mon, 4 May 2026 14:19:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777904347; bh=t46b3yJOP5936Uj8m4r4LoRvvYzgQGm0EMYJgTWBrWE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tOKliuhURtRTp4yxQNmBFw2BDrrUXyA9+6mI2orAJ3i5Te0m+u312MQ7/x7V6YJRO nLin7z8g+nIhxtfjqfN7a6jJ5EIRIVGwUexISfu/2j0rjzaJHaIFU33dGBSr0s/7ie 5K6uw+iRC7eOvmLHcVvRIpWX9/1x/YntHOw4/Wbs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+8fa95c41eafbc9d2ff6f@syzkaller.appspotmail.com, Takashi Iwai , =?UTF-8?q?C=C3=A1ssio=20Gabriel?= , Takashi Iwai Subject: [PATCH 6.18 270/275] ALSA: aloop: Fix peer runtime UAF during format-change stop Date: Mon, 4 May 2026 15:53:30 +0200 Message-ID: <20260504135153.063431828@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260504135142.929052779@linuxfoundation.org> References: <20260504135142.929052779@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Cássio Gabriel commit e5c33cdc6f402eab8abd36ecf436b22c9d3a8aff upstream. loopback_check_format() may stop the capture side when playback starts with parameters that no longer match a running capture stream. Commit 826af7fa62e3 ("ALSA: aloop: Fix racy access at PCM trigger") moved the peer lookup under cable->lock, but the actual snd_pcm_stop() still runs after dropping that lock. A concurrent close can clear the capture entry from cable->streams[] and detach or free its runtime while the playback trigger path still holds a stale peer substream pointer. Keep a per-cable count of in-flight peer stops before dropping cable->lock, and make free_cable() wait for those stops before detaching the runtime. This preserves the existing behavior while making the peer runtime lifetime explicit. Reported-by: syzbot+8fa95c41eafbc9d2ff6f@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=8fa95c41eafbc9d2ff6f Fixes: 597603d615d2 ("ALSA: introduce the snd-aloop module for the PCM loopback") Cc: stable@vger.kernel.org Suggested-by: Takashi Iwai Signed-off-by: Cássio Gabriel Link: https://patch.msgid.link/20260424-alsa-aloop-peer-stop-uaf-v2-1-94e68101db8a@gmail.com Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/drivers/aloop.c | 43 ++++++++++++++++++++++++++++++------------- 1 file changed, 30 insertions(+), 13 deletions(-) --- a/sound/drivers/aloop.c +++ b/sound/drivers/aloop.c @@ -99,6 +99,9 @@ struct loopback_ops { struct loopback_cable { spinlock_t lock; struct loopback_pcm *streams[2]; + /* in-flight peer stops running outside cable->lock */ + atomic_t stop_count; + wait_queue_head_t stop_wait; struct snd_pcm_hardware hw; /* flags */ unsigned int valid; @@ -366,8 +369,11 @@ static int loopback_check_format(struct return 0; if (stream == SNDRV_PCM_STREAM_CAPTURE) return -EIO; - else if (cruntime->state == SNDRV_PCM_STATE_RUNNING) + else if (cruntime->state == SNDRV_PCM_STATE_RUNNING) { + /* close must not free the peer runtime below */ + atomic_inc(&cable->stop_count); stop_capture = true; + } } setup = get_setup(dpcm_play); @@ -396,8 +402,11 @@ static int loopback_check_format(struct } } - if (stop_capture) + if (stop_capture) { snd_pcm_stop(dpcm_capt->substream, SNDRV_PCM_STATE_DRAINING); + if (atomic_dec_and_test(&cable->stop_count)) + wake_up(&cable->stop_wait); + } return 0; } @@ -1049,23 +1058,29 @@ static void free_cable(struct snd_pcm_su struct loopback *loopback = substream->private_data; int dev = get_cable_index(substream); struct loopback_cable *cable; + struct loopback_pcm *dpcm; + bool other_alive; cable = loopback->cables[substream->number][dev]; if (!cable) return; - if (cable->streams[!substream->stream]) { - /* other stream is still alive */ - guard(spinlock_irq)(&cable->lock); - cable->streams[substream->stream] = NULL; - } else { - struct loopback_pcm *dpcm = substream->runtime->private_data; - if (cable->ops && cable->ops->close_cable && dpcm) - cable->ops->close_cable(dpcm); - /* free the cable */ - loopback->cables[substream->number][dev] = NULL; - kfree(cable); + scoped_guard(spinlock_irq, &cable->lock) { + cable->streams[substream->stream] = NULL; + other_alive = cable->streams[!substream->stream]; } + + /* Pair with the stop_count increment in loopback_check_format(). */ + wait_event(cable->stop_wait, !atomic_read(&cable->stop_count)); + if (other_alive) + return; + + dpcm = substream->runtime->private_data; + if (cable->ops && cable->ops->close_cable && dpcm) + cable->ops->close_cable(dpcm); + /* free the cable */ + loopback->cables[substream->number][dev] = NULL; + kfree(cable); } static int loopback_jiffies_timer_open(struct loopback_pcm *dpcm) @@ -1260,6 +1275,8 @@ static int loopback_open(struct snd_pcm_ goto unlock; } spin_lock_init(&cable->lock); + atomic_set(&cable->stop_count, 0); + init_waitqueue_head(&cable->stop_wait); cable->hw = loopback_pcm_hardware; if (loopback->timer_source) cable->ops = &loopback_snd_timer_ops;