[PATCH AUTOSEL 4.9 15/16] Bluetooth: L2CAP: Fix user-after-free

From: Sasha Levin
Date: Sun Oct 09 2022 - 18:57:09 EST


From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>

[ 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@xxxxxxxxxx
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
Signed-off-by: Sungwoo Kim <iam@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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