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Subject: Re: [PATCH] net: bluetooth: cmtp: fix file refcount when
 cmtp_attach_device fails
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20210413162103.435467-1-cascardo@canonical.com>
Date:   Tue, 13 Apr 2021 20:40:45 +0200
Cc:     "open list:BLUETOOTH DRIVERS" <linux-bluetooth@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>, isdn@linux-pingi.de,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>
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Message-Id: <0E9D2620-A821-410F-9DED-4465568F6701@holtmann.org>
References: <20210413162103.435467-1-cascardo@canonical.com>
To:     Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Precedence: bulk

Hi Thadeu,

> When cmtp_attach_device fails, cmtp_add_connection returns the error value
> which leads to the caller to doing fput through sockfd_put. But
> cmtp_session kthread, which is stopped in this path will also call fput,
> leading to a potential refcount underflow or a use-after-free.
> 
> Add a refcount before we signal the kthread to stop. The kthread will try
> to grab the cmtp_session_sem mutex before doing the fput, which is held
> when get_file is called, so there should be no races there.
> 
> Reported-by: Ryota Shiga
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> ---
> net/bluetooth/cmtp/core.c | 5 +++++
> 1 file changed, 5 insertions(+)

Patch has been applied to bluetooth-next tree.

Regards

Marcel