[PATCH AUTOSEL 4.4 22/64] Bluetooth: prefetch channel before killing sock

Sasha Levin
2020-09-18T02:22:13Z

From: Hillf Danton <hdanton@sina.com>

[ Upstream commit 2a154903cec20fb64ff4d7d617ca53c16f8fd53a ]

Prefetch channel before killing sock in order to fix UAF like

BUG: KASAN: use-after-free in l2cap_sock_release+0x24c/0x290 net/bluetooth/l2cap_sock.c:1212
Read of size 8 at addr ffff8880944904a0 by task syz-fuzzer/9751

Reported-by: syzbot+c3c5bdea7863886115dc@syzkaller.appspotmail.com
Fixes: 6c08fc896b60 ("Bluetooth: Fix refcount use-after-free issue")
Cc: Manish Mandlik <mmandlik@google.com>
Signed-off-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bluetooth/l2cap_sock.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index cb024c25530a3..e562385d9440e 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1189,6 +1189,7 @@ static int l2cap_sock_release(struct socket *sock)
{
struct sock *sk = sock->sk;
int err;
+ struct l2cap_chan *chan;

BT_DBG("sock %p, sk %p", sock, sk);

@@ -1198,15 +1199,16 @@ static int l2cap_sock_release(struct socket *sock)
bt_sock_unlink(&l2cap_sk_list, sk);

err = l2cap_sock_shutdown(sock, 2);
+ chan = l2cap_pi(sk)->chan;

- l2cap_chan_hold(l2cap_pi(sk)->chan);
- l2cap_chan_lock(l2cap_pi(sk)->chan);
+ l2cap_chan_hold(chan);
+ l2cap_chan_lock(chan);

sock_orphan(sk);
l2cap_sock_kill(sk);

- l2cap_chan_unlock(l2cap_pi(sk)->chan);
- l2cap_chan_put(l2cap_pi(sk)->chan);
+ l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return err;
}
--
2.25.1