Forwarded: [PATCH] media: rtl2832: fix use-after-free in rtl2832_remove()

[syzbot <syzbot+019ced393ab913002b75@syzkaller.appspotmail.com>]

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Subject: [PATCH] media: rtl2832: fix use-after-free in rtl2832_remove()
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master


cancel_delayed_work_sync() is called before i2c_mux_del_adapters(),
but i2c_mux_del_adapters() internally performs I2C transfers which
trigger rtl2832_deselect(), which reschedules i2c_gate_work via
schedule_delayed_work(). This re-arms the timer after it has been
cancelled, causing a use-after-free when kfree(dev) is called and
the timer later fires on freed memory.

Fix this by calling i2c_mux_del_adapters() before
cancel_delayed_work_sync(). Once i2c_mux_del_adapters() completes,
no further I2C transfers can go through the mux, so rtl2832_deselect()
can never re-arm the timer again, making the cancellation truly final.

Reported-by: syzbot+019ced393ab913002b75@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=019ced393ab913002b75
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
---
 drivers/media/dvb-frontends/rtl2832.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/dvb-frontends/rtl2832.c b/drivers/media/dvb-frontends/rtl2832.c
index d8e1546aea5e..9898f729304a 100644
--- a/drivers/media/dvb-frontends/rtl2832.c
+++ b/drivers/media/dvb-frontends/rtl2832.c
@@ -1115,10 +1115,10 @@ static void rtl2832_remove(struct i2c_client *client)
 
 	dev_dbg(&client->dev, "\n");
 
-	cancel_delayed_work_sync(&dev->i2c_gate_work);
-
 	i2c_mux_del_adapters(dev->muxc);
 
+	cancel_delayed_work_sync(&dev->i2c_gate_work);
+
 	regmap_exit(dev->regmap);
 
 	kfree(dev);
-- 
2.43.0