From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 824963D668F; Tue, 16 Jun 2026 19:02:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781636530; cv=none; b=so1m/KgSke1+J62mLuYyklUqvHeJSkZGbUHb2BolJemILV9GttJYY5Y7E/7uuqeNs8gRrycK1k6HsytRnSGNN6LUmPQbrJmVBhdgubM0N6lFumJHfyC+bQhsAmYokhUhPMptFkoptD7LiXHJHZfH2IEJyS9TQJHV55G6HRcnQDM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781636530; c=relaxed/simple; bh=h5q87jY3vhagRd0OIa5WOTAjoSvLJgqPI7lKE5shfZA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=k6Jbguif/wKf3l5JJs11ZA4cRvBnpz0/wCUyAMWUKxi1JSzrNfxXOrmfTLFeOZeKb1q56/gpbptIZKAzmic0R+Fby66KEp0zJOUeKT0oIM4vdHp16S1MewvCHokCRaT7eiZ0khggVGigs6asEXQvraEPL85VcLrn8+4OgXWDA2s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=uNudtdWX; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="uNudtdWX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3820A1F000E9; Tue, 16 Jun 2026 19:02:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781636529; bh=3mi4FLn4kTXOAMcMIjbu9FLd7JAlVcUB1+QnA10C75E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=uNudtdWX/V6xNiJVbynzlklWWSfxjxrkziJKM6hhZggkSvjkbgAknNNah6c58DNGV JDhe/hjZiBqwZTcPxbWBq1oJLvz8Vie7YYIXA77XSP5Hmvvemte6uJVtmMA6pJb9/D qsnjMsYItIKBT1QLME7n1V4aKHJ/cCKIEX9dBwu4= 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 , Sasha Levin Subject: [PATCH 5.10 249/342] ALSA: aloop: Fix peer runtime UAF during format-change stop Date: Tue, 16 Jun 2026 20:29:05 +0530 Message-ID: <20260616145059.831355928@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145048.348037099@linuxfoundation.org> References: <20260616145048.348037099@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore 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 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Cássio Gabriel [ Upstream commit e5c33cdc6f402eab8abd36ecf436b22c9d3a8aff ] 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 [ collapsed inc/snd_pcm_stop/dec into the existing inline call site and used spin_lock_irq/unlock_irq instead of scoped_guard ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- sound/drivers/aloop.c | 40 +++++++++++++++++++++++++++------------- 1 file changed, 27 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; @@ -342,8 +345,12 @@ static int loopback_check_format(struct if (stream == SNDRV_PCM_STREAM_CAPTURE) { return -EIO; } else { + /* close must not free the peer runtime below */ + atomic_inc(&cable->stop_count); snd_pcm_stop(cable->streams[SNDRV_PCM_STREAM_CAPTURE]-> substream, SNDRV_PCM_STATE_DRAINING); + if (atomic_dec_and_test(&cable->stop_count)) + wake_up(&cable->stop_wait); __notify: runtime = cable->streams[SNDRV_PCM_STREAM_PLAYBACK]-> substream->runtime; @@ -995,24 +1002,29 @@ 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 */ - spin_lock_irq(&cable->lock); - cable->streams[substream->stream] = NULL; - spin_unlock_irq(&cable->lock); - } 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); - } + spin_lock_irq(&cable->lock); + cable->streams[substream->stream] = NULL; + other_alive = cable->streams[!substream->stream] != NULL; + spin_unlock_irq(&cable->lock); + + /* 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) @@ -1207,6 +1219,8 @@ 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;