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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, syzkaller <syzkaller@googlegroups.com>,
        Dongliang Mu <mudongliangabcd@gmail.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 313/913] media: em28xx: initialize refcount before kref_get
Date:   Tue,  5 Apr 2022 09:22:55 +0200
Message-Id: <20220405070349.235758782@linuxfoundation.org>
In-Reply-To: <20220405070339.801210740@linuxfoundation.org>
References: <20220405070339.801210740@linuxfoundation.org>
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From: Dongliang Mu <mudongliangabcd@gmail.com>

[ Upstream commit c08eadca1bdfa099e20a32f8fa4b52b2f672236d ]

The commit 47677e51e2a4("[media] em28xx: Only deallocate struct
em28xx after finishing all extensions") adds kref_get to many init
functions (e.g., em28xx_audio_init). However, kref_init is called too
late in em28xx_usb_probe, since em28xx_init_dev before will invoke
those init functions and call kref_get function. Then refcount bug
occurs in my local syzkaller instance.

Fix it by moving kref_init before em28xx_init_dev. This issue occurs
not only in dev but also dev->dev_next.

Fixes: 47677e51e2a4 ("[media] em28xx: Only deallocate struct em28xx after finishing all extensions")
Reported-by: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/usb/em28xx/em28xx-cards.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index ebc430b05f21..c415b1d195c4 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -3931,6 +3931,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
 		goto err_free;
 	}
 
+	kref_init(&dev->ref);
+
 	dev->devno = nr;
 	dev->model = id->driver_info;
 	dev->alt   = -1;
@@ -4031,6 +4033,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
 	}
 
 	if (dev->board.has_dual_ts && em28xx_duplicate_dev(dev) == 0) {
+		kref_init(&dev->dev_next->ref);
+
 		dev->dev_next->ts = SECONDARY_TS;
 		dev->dev_next->alt   = -1;
 		dev->dev_next->is_audio_only = has_vendor_audio &&
@@ -4085,12 +4089,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
 			em28xx_write_reg(dev, 0x0b, 0x82);
 			mdelay(100);
 		}
-
-		kref_init(&dev->dev_next->ref);
 	}
 
-	kref_init(&dev->ref);
-
 	request_modules(dev);
 
 	/*
-- 
2.34.1