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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,
        Luiz Augusto von Dentz <luiz.von.dentz@intel.com>,
        Sungwoo Kim <iam@sung-woo.kim>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 135/159] Bluetooth: L2CAP: Fix user-after-free
Date:   Mon, 24 Oct 2022 13:31:29 +0200
Message-Id: <20221024112954.396342352@linuxfoundation.org>
In-Reply-To: <20221024112949.358278806@linuxfoundation.org>
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From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

[ Upstream commit 35fcbc4243aad7e7d020b7c1dfb14bb888b20a4f ]

This uses l2cap_chan_hold_unless_zero() after calling
__l2cap_get_chan_blah() to prevent the following trace:

Bluetooth: l2cap_core.c:static void l2cap_chan_destroy(struct kref
*kref)
Bluetooth: chan 0000000023c4974d
Bluetooth: parent 00000000ae861c08
==================================================================
BUG: KASAN: use-after-free in __mutex_waiter_is_first
kernel/locking/mutex.c:191 [inline]
BUG: KASAN: use-after-free in __mutex_lock_common
kernel/locking/mutex.c:671 [inline]
BUG: KASAN: use-after-free in __mutex_lock+0x278/0x400
kernel/locking/mutex.c:729
Read of size 8 at addr ffff888006a49b08 by task kworker/u3:2/389

Link: https://lore.kernel.org/lkml/20220622082716.478486-1-lee.jones@linaro.org
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/bluetooth/l2cap_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 42df17fa7f16..ec04a7ea5537 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4039,6 +4039,12 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 		}
 	}
 
+	chan = l2cap_chan_hold_unless_zero(chan);
+	if (!chan) {
+		err = -EBADSLT;
+		goto unlock;
+	}
+
 	err = 0;
 
 	l2cap_chan_lock(chan);
@@ -4068,6 +4074,7 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 	}
 
 	l2cap_chan_unlock(chan);
+	l2cap_chan_put(chan);
 
 unlock:
 	mutex_unlock(&conn->chan_lock);
-- 
2.35.1