linux-kernel - Re: [PATCH 4.19 027/168] Bluetooth: add a mutex lock to avoid UAF in do_enale

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Date:   Tue, 18 Aug 2020 11:40:25 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+96414aa0033c363d8458@...kaller.appspotmail.com,
        Lihong Kou <koulihong@...wei.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 027/168] Bluetooth: add a mutex lock to avoid UAF in
 do_enale_set

Hi!

> From: Lihong Kou <koulihong@...wei.com>
> 
> [ Upstream commit f9c70bdc279b191da8d60777c627702c06e4a37d ]
> 
> In the case we set or free the global value listen_chan in
> different threads, we can encounter the UAF problems because
> the method is not protected by any lock, add one to avoid
> this bug.

For this to be safe, bt_6lowpan_exit() needs same handling, no?

Signed-off-by: Pavel Machek (CIP) <pavel@...x.de>

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 9a75f9b00b51..2402ef5ac072 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -1304,10 +1304,12 @@ static void __exit bt_6lowpan_exit(void)
 	debugfs_remove(lowpan_enable_debugfs);
 	debugfs_remove(lowpan_control_debugfs);
 
+	mutex_lock(&set_lock);
 	if (listen_chan) {
 		l2cap_chan_close(listen_chan, 0);
 		l2cap_chan_put(listen_chan);
 	}
+	mutex_unlock(&set_lock);
 
 	disconnect_devices();
 


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