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

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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()
in rtl2832_remove(). If i2c_mux_del_adapters() triggers any I2C
transfers through the mux adapter, rtl2832_deselect() will be called
which reschedules i2c_gate_work via schedule_delayed_work(). This
re-arms the timer after it was cancelled, causing a use-after-free
when kfree(dev) is called and the timer later fires on freed memory.

Fix this by moving cancel_delayed_work_sync() to after
i2c_mux_del_adapters(), ensuring the cancellation is the last
operation before kfree(dev).

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 | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/media/dvb-frontends/rtl2832.c b/drivers/media/dvb-frontends/rtl2832.c
index d8e1546aea5e..ce3326feaa7d 100644
--- a/drivers/media/dvb-frontends/rtl2832.c
+++ b/drivers/media/dvb-frontends/rtl2832.c
@@ -821,6 +821,9 @@ static int rtl2832_deselect(struct i2c_mux_core *muxc, u32 chan_id)
 {
 	struct rtl2832_dev *dev = i2c_mux_priv(muxc);
 
+	pr_err("rtl2832_deselect called from: %pS\n",
+           __builtin_return_address(0));
+
 	schedule_delayed_work(&dev->i2c_gate_work, usecs_to_jiffies(100));
 	return 0;
 }
@@ -1113,12 +1116,18 @@ static void rtl2832_remove(struct i2c_client *client)
 {
 	struct rtl2832_dev *dev = i2c_get_clientdata(client);
 
+	pr_err("rtl2832_remove: before cancel\n");
+
 	dev_dbg(&client->dev, "\n");
 
 	cancel_delayed_work_sync(&dev->i2c_gate_work);
 
+	pr_err("rtl2832_remove: before i2c_mux_del_adapters\n");
+
 	i2c_mux_del_adapters(dev->muxc);
 
+	pr_err("rtl2832_remove: before kfree\n");
+
 	regmap_exit(dev->regmap);
 
 	kfree(dev);
-- 
2.43.0