netdev - [PATCH AUTOSEL 4.19 23/25] Bluetooth: L2CAP: Fix user-after-free

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Date:   Sun,  9 Oct 2022 18:24:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Luiz Augusto von Dentz <luiz.von.dentz@...el.com>,
        Sungwoo Kim <iam@...g-woo.kim>,
        Sasha Levin <sashal@...nel.org>, marcel@...tmann.org,
        johan.hedberg@...il.com, luiz.dentz@...il.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 23/25] Bluetooth: L2CAP: Fix user-after-free

From: Luiz Augusto von Dentz <luiz.von.dentz@...el.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@...el.com>
Signed-off-by: Sungwoo Kim <iam@...g-woo.kim>
Signed-off-by: Sasha Levin <sashal@...nel.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 7c280fcdcaa0..5c965f7b1709 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4049,6 +4049,12 @@ 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);
@@ -4078,6 +4084,7 @@ 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