linux-kernel - Re: [PATCH 2/2] USB(u_serial.c): it has a NULL point

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Date:   Wed, 13 Nov 2019 07:13:38 +0000
From:   Peter Chen <peter.chen@....com>
To:     hui yang <yanghui.def@...il.com>
CC:     Greg KH <gregkh@...uxfoundation.org>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "mirq-linux@...e.qmqm.pl" <mirq-linux@...e.qmqm.pl>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] USB(u_serial.c): it has a NULL point

On 19-11-09 15:49:13, hui yang wrote:
> I'm sorry for my fault . Now I send to everyone .
> 
> When we use USB to transmit data
> with PC, the phone will crashed Low probability .
> We found port->port.tty became NULL.

Would you please debug more, it seems gs open/close (gs_open/gs_close)
are something wrong. The value port->port.tty and port->port.count
are inconsistent.

Peter

> 
> Thanks
> 
> Greg KH <gregkh@...uxfoundation.org> 于2019年11月3日周日 下午8:42写道：
> >
> > On Sun, Nov 03, 2019 at 10:44:04AM +0800, hui yang wrote:
> > > From: YangHui <yanghui.def@...il.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@...il.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

-- 

Thanks,
Peter Chen