linux-kernel - Re: [PATCH] serial-uartlite: Fix null-ptr-deref in ulite

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Date:   Tue, 21 May 2019 12:10:59 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     YueHaibing <yuehaibing@...wei.com>, jacmet@...site.dk,
        jslaby@...e.com, shubhrajyoti.datta@...inx.com,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] serial-uartlite: Fix null-ptr-deref in ulite_exit

On Fri, May 17, 2019 at 09:55:02AM +0200, Johan Hovold wrote:
> On Thu, May 16, 2019 at 12:09:31PM +0800, YueHaibing wrote:
> > If ulite_probe is not called or failed to registed
> > uart_register_driver, unload the module will call
> > uart_unregister_driver, which will tigger NULL
> > pointer dereference like this:
> > 
> > BUG: KASAN: null-ptr-deref in tty_unregister_driver+0x19/0x100
> > Read of size 4 at addr 0000000000000034 by task syz-executor.0/4246
> 
> > This patch fix this by moving uart_unregister_driver
> > to ulite_remove.
> > 
> > Reported-by: Hulk Robot <hulkci@...wei.com>
> > Fixes: 415b43bdb008 ("tty: serial: uartlite: Move uart register to probe")
> > Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> > ---
> >  drivers/tty/serial/uartlite.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c
> > index b8b912b..2e49fb6 100644
> > --- a/drivers/tty/serial/uartlite.c
> > +++ b/drivers/tty/serial/uartlite.c
> > @@ -867,6 +867,7 @@ static int ulite_remove(struct platform_device *pdev)
> >  	pm_runtime_disable(&pdev->dev);
> >  	pm_runtime_set_suspended(&pdev->dev);
> >  	pm_runtime_dont_use_autosuspend(&pdev->dev);
> > +	uart_unregister_driver(&ulite_uart_driver);
> 
> This broken. Consider what happens if you have tho ports registered and
> you unbind the first.
> 
> Someone else sent a fix for this here
> 
> 	https://lkml.kernel.org/r/20190514033219.169947-1-wangkefeng.wang@huawei.com
> 
> That fix also has some issues, but is still better given the current
> state this driver is in.

I'm not taking any of these patches until people agree on what needs to
be done here :)

Why is this driver so "special" it is having these types of problems?
Why can't it do what all other drivers do in this case?

thanks,

greg k-h