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 7D66B3A9624 for ; Mon, 4 May 2026 12:45:47 +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=1777898747; cv=none; b=kqPdJrVNLiqhNpslcHvbcma7t8gr4lRgK9un5mNDIIFOE1i6lNyDzcfHeBEf+1GT3mRVJxepG1qBT0hXHMH0dljL6RHPbP4jUgSA+fxywBDXeu3q61vqDkfTWiuRn91Jv2vUt60sEoNVPzFffA5xyDBOHbuN1l0ewJXR5Hfle+M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777898747; c=relaxed/simple; bh=vQOFv9c0bY8tzavfxrC8iwOMfxcrn4faiJF9ETFJ1lQ=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=XfDZUwzpGsATrCGV5LjqUZpnQsWsqYIaHnPvJkVrMzJyzrUs3cGEhVeFimsci6V+LeXDUT5n2PVeKKe84VUXpxDBsDF8iar8Eo1PF6EOMv9RTlMgGtIDftWWShgZ63k1ORYN7ofHRxtqMlWSxugxEx3GI58vCWPuQU7+U9ymxPk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=RGR3d9hF; 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="RGR3d9hF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6864C2BCF5; Mon, 4 May 2026 12:45:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777898747; bh=vQOFv9c0bY8tzavfxrC8iwOMfxcrn4faiJF9ETFJ1lQ=; h=Subject:To:Cc:From:Date:From; b=RGR3d9hFrdBNXZWCTmFaBVprBD7eMKf0F1DAkrlosek4KN3bcesFwpZqwB3JENH68 DipVoahsrLM4mopZ9VFZe9SRMRXaNY3fH46D3eg/JxiA8c07WB6rs+ufRfwyzOyDsL HSp0Tk4RuTVoSfz4lUyDKvNZFjGTzwbsTd/4KRxI= Subject: FAILED: patch "[PATCH] ALSA: aloop: Fix peer runtime UAF during format-change stop" failed to apply to 6.12-stable tree To: cassiogabrielcontato@gmail.com,tiwai@suse.com,tiwai@suse.de Cc: From: Date: Mon, 04 May 2026 14:45:44 +0200 Message-ID: <2026050444-porcupine-unlined-e9a8@gregkh> 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 The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x e5c33cdc6f402eab8abd36ecf436b22c9d3a8aff # git commit -s git send-email --to '' --in-reply-to '2026050444-porcupine-unlined-e9a8@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From e5c33cdc6f402eab8abd36ecf436b22c9d3a8aff Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?C=C3=A1ssio=20Gabriel?= Date: Fri, 24 Apr 2026 09:48:41 -0300 Subject: [PATCH] ALSA: aloop: Fix peer runtime UAF during format-change stop MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c index aa0d2fcb1a18..a37a1695f51c 100644 --- 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 loopback_cable *cable, int stream) 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 loopback_cable *cable, int stream) } } - 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_substream *substream) 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_substream *substream) 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;