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Subject: Re: [PATCH 5.4 39/78] Bluetooth: use correct lock to prevent UAF of
 hdev object
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     stable@vger.kernel.org, Lin Ma <linma@zju.edu.cn>,
        Marcel Holtmann <marcel@holtmann.org>
References: <20210608175935.254388043@linuxfoundation.org>
 <20210608175936.584233292@linuxfoundation.org>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <def3c8d4-a787-8536-e743-adf90a0c5352@gmail.com>
Date:   Mon, 14 Jun 2021 16:15:02 +0200
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On 6/8/21 8:27 PM, Greg Kroah-Hartman wrote:
> From: Lin Ma <linma@zju.edu.cn>
> 
> commit e305509e678b3a4af2b3cfd410f409f7cdaabb52 upstream.
> 
> The hci_sock_dev_event() function will cleanup the hdev object for
> sockets even if this object may still be in used within the
> hci_sock_bound_ioctl() function, result in UAF vulnerability.
> 
> This patch replace the BH context lock to serialize these affairs
> and prevent the race condition.
> 
> Signed-off-by: Lin Ma <linma@zju.edu.cn>
> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  net/bluetooth/hci_sock.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/net/bluetooth/hci_sock.c
> +++ b/net/bluetooth/hci_sock.c
> @@ -755,7 +755,7 @@ void hci_sock_dev_event(struct hci_dev *
>  		/* Detach sockets from device */
>  		read_lock(&hci_sk_list.lock);
>  		sk_for_each(sk, &hci_sk_list.head) {
> -			bh_lock_sock_nested(sk);
> +			lock_sock(sk);
>  			if (hci_pi(sk)->hdev == hdev) {
>  				hci_pi(sk)->hdev = NULL;
>  				sk->sk_err = EPIPE;
> @@ -764,7 +764,7 @@ void hci_sock_dev_event(struct hci_dev *
>  
>  				hci_dev_put(hdev);
>  			}
> -			bh_unlock_sock(sk);
> +			release_sock(sk);
>  		}
>  		read_unlock(&hci_sk_list.lock);
>  	}
> 
> 


This patch is buggy.

lock_sock() can sleep.

But the read_lock(&hci_sk_list.lock) two lines before is not going to allow the sleep.

Hmmm ?