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Date:   Sun, 3 Nov 2019 13:42:01 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     hui yang <yanghui.def@gmail.com>
Cc:     balbi@kernel.org, mirq-linux@rere.qmqm.pl,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] USB(u_serial.c): it has a NULL point
Message-ID: <20191103124201.GB619218@kroah.com>
References: <1572749044-6091-1-git-send-email-yanghui.def@gmail.com>
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On Sun, Nov 03, 2019 at 10:44:04AM +0800, hui yang wrote:
> From: YangHui <yanghui.def@gmail.com>
> 
> Unable to handle kernel NULL pointer dereference at virtual address 000002a0
> Kernel BUG at tty_wakeup+0x18/0x8c
> [<0000000095135e9d>] tty_wakeup+0x18/0x8c
> [<00000000c35f19e4>] gs_start_io+0xc8/0x158
> [<00000000b11b184e>] gserial_connect+0xd0/0x174
> [<00000000642201de>] acm_set_alt+0x70/0x180
> [<00000000a9d38e8b>] composite_setup+0x1848/0x1a7c
> [<0000000072c88781>] android_setup+0x1ec/0x1f4
> [<000000004c0127a5>] msm_udc_irq+0x8d0/0xc0c
> [<00000000f8bb9acf>] __handle_irq_event_percpu+0x74/0x294
> [<00000000afd57256>] handle_irq_event+0x60/0xc8
> [<0000000076719b24>] handle_fasteoi_irq+0xc8/0x1c4
> [<00000000421f3d87>] generic_handle_irq+0x34/0x4c
> [<00000000b2f2d343>] __handle_domain_irq+0x6c/0xbc
> [<00000000c74325e8>] gic_handle_irq+0x6c/0xe0
> yes,we can see the port->port.tty==NULL, so system crashed
> 
> Signed-off-by: YangHui <yanghui.def@gmail.com>
> ---
>  drivers/usb/gadget/function/u_serial.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index 65f634e..a1c2ac2 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -562,6 +562,8 @@ static int gs_start_io(struct gs_port *port)
>  
>  	/* unblock any pending writes into our circular buffer */
>  	if (started) {
> +		if (port->port.tty == NULL)
> +			return -EIO;

How can this happen?  Shouldn't this be handled earlier?

If not, can you document this how this can be true and what should be
done about it?

thanks,

greg k-h