netdev - Re: [PATCH] Bluetooth: check for zapped sk before connecting

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Message-Id: <559FCF7C-A929-4291-956C-EF776EFAA47D@holtmann.org>
Date:   Mon, 22 Mar 2021 16:53:08 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Archie Pusaka <apusaka@...gle.com>
Cc:     linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        CrosBT Upstreaming <chromeos-bluetooth-upstreaming@...omium.org>,
        Archie Pusaka <apusaka@...omium.org>,
        syzbot+abfc0f5e668d4099af73@...kaller.appspotmail.com,
        Alain Michaud <alainm@...omium.org>,
        Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: check for zapped sk before connecting

Hi Archie,

> There is a possibility of receiving a zapped sock on
> l2cap_sock_connect(). This could lead to interesting crashes, one
> such case is tearing down an already tore l2cap_sock as is happened
> with this call trace:
> 
> __dump_stack lib/dump_stack.c:15 [inline]
> dump_stack+0xc4/0x118 lib/dump_stack.c:56
> register_lock_class kernel/locking/lockdep.c:792 [inline]
> register_lock_class+0x239/0x6f6 kernel/locking/lockdep.c:742
> __lock_acquire+0x209/0x1e27 kernel/locking/lockdep.c:3105
> lock_acquire+0x29c/0x2fb kernel/locking/lockdep.c:3599
> __raw_spin_lock_bh include/linux/spinlock_api_smp.h:137 [inline]
> _raw_spin_lock_bh+0x38/0x47 kernel/locking/spinlock.c:175
> spin_lock_bh include/linux/spinlock.h:307 [inline]
> lock_sock_nested+0x44/0xfa net/core/sock.c:2518
> l2cap_sock_teardown_cb+0x88/0x2fb net/bluetooth/l2cap_sock.c:1345
> l2cap_chan_del+0xa3/0x383 net/bluetooth/l2cap_core.c:598
> l2cap_chan_close+0x537/0x5dd net/bluetooth/l2cap_core.c:756
> l2cap_chan_timeout+0x104/0x17e net/bluetooth/l2cap_core.c:429
> process_one_work+0x7e3/0xcb0 kernel/workqueue.c:2064
> worker_thread+0x5a5/0x773 kernel/workqueue.c:2196
> kthread+0x291/0x2a6 kernel/kthread.c:211
> ret_from_fork+0x4e/0x80 arch/x86/entry/entry_64.S:604
> 
> Signed-off-by: Archie Pusaka <apusaka@...omium.org>
> Reported-by: syzbot+abfc0f5e668d4099af73@...kaller.appspotmail.com
> Reviewed-by: Alain Michaud <alainm@...omium.org>
> Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> Reviewed-by: Guenter Roeck <groeck@...omium.org>
> ---
> 
> net/bluetooth/l2cap_sock.c | 7 +++++++
> 1 file changed, 7 insertions(+)
> 
> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> index f1b1edd0b697..b86fd8cc4dc1 100644
> --- a/net/bluetooth/l2cap_sock.c
> +++ b/net/bluetooth/l2cap_sock.c
> @@ -182,6 +182,13 @@ static int l2cap_sock_connect(struct socket *sock, struct sockaddr *addr,
> 
> 	BT_DBG("sk %p", sk);
> 
> +	lock_sock(sk);
> +	if (sock_flag(sk, SOCK_ZAPPED)) {
> +		release_sock(sk);
> +		return -EINVAL;
> +	}
> +	release_sock(sk);
> +

hmmm. I wonder if this would look better and easy to see that the locking is done correctly.

	lock_sock(sk);
	zapped = sock_flag(sk, SOCK_ZAPPED);
	release_sock(sk);

	if (zapped)
		return -EINVAL;

Regards

Marcel