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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Takashi Iwai <tiwai@suse.de>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 086/121] ALSA: hda: Fix potential race in unsol event handler
Date:   Tue, 29 Sep 2020 13:00:30 +0200
Message-Id: <20200929105934.438541203@linuxfoundation.org>
In-Reply-To: <20200929105930.172747117@linuxfoundation.org>
References: <20200929105930.172747117@linuxfoundation.org>
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From: Takashi Iwai <tiwai@suse.de>

[ Upstream commit c637fa151259c0f74665fde7cba5b7eac1417ae5 ]

The unsol event handling code has a loop retrieving the read/write
indices and the arrays without locking while the append to the array
may happen concurrently.  This may lead to some inconsistency.
Although there hasn't been any proof of this bad results, it's still
safer to protect the racy accesses.

This patch adds the spinlock protection around the unsol handling loop
for addressing it.  Here we take bus->reg_lock as the writer side
snd_hdac_bus_queue_event() is also protected by that lock.

Link: https://lore.kernel.org/r/20200516062556.30951-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 sound/hda/hdac_bus.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sound/hda/hdac_bus.c b/sound/hda/hdac_bus.c
index 0e81ea89a5965..e3f68a76d90eb 100644
--- a/sound/hda/hdac_bus.c
+++ b/sound/hda/hdac_bus.c
@@ -155,6 +155,7 @@ static void process_unsol_events(struct work_struct *work)
 	struct hdac_driver *drv;
 	unsigned int rp, caddr, res;
 
+	spin_lock_irq(&bus->reg_lock);
 	while (bus->unsol_rp != bus->unsol_wp) {
 		rp = (bus->unsol_rp + 1) % HDA_UNSOL_QUEUE_SIZE;
 		bus->unsol_rp = rp;
@@ -166,10 +167,13 @@ static void process_unsol_events(struct work_struct *work)
 		codec = bus->caddr_tbl[caddr & 0x0f];
 		if (!codec || !codec->dev.driver)
 			continue;
+		spin_unlock_irq(&bus->reg_lock);
 		drv = drv_to_hdac_driver(codec->dev.driver);
 		if (drv->unsol_event)
 			drv->unsol_event(codec, res);
+		spin_lock_irq(&bus->reg_lock);
 	}
+	spin_unlock_irq(&bus->reg_lock);
 }
 
 /**
-- 
2.25.1