Re: [PATCH] serial-uartlite: Fix null-ptr-deref in ulite_exit

[Johan Hovold <johan@kernel.org>]

On Tue, May 21, 2019 at 12:10:59PM +0200, Greg Kroah-Hartman wrote:
> 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@huawei.com>
> > > Fixes: 415b43bdb008 ("tty: serial: uartlite: Move uart register to probe")
> > > Signed-off-by: YueHaibing <yuehaibing@huawei.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 :)

Good. :)

> 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?

Apparently some vendor-tree hacks has made it into mainline. They're
trying to register one tty/uart driver per physical port which sounds
like a terrible idea. And even the implementation is broken as these bug
reports indicate.

A series was apparently first posted for xilinks_uartps.c, but that one
has not yet been merged AFAICT. A similar series was later posted for
uartlite.c, but only the first half or so got in:

	https://lkml.kernel.org/r/1539685088-13465-1-git-send-email-shubhrajyoti.datta@gmail.com

Actually, it looks like the problems started already with:

	https://lkml.kernel.org/r/1533545534-24458-1-git-send-email-shubhrajyoti.datta@gmail.com

So the first broken commit is

	415b43bdb008 ("tty: serial: uartlite: Move uart register to probe")

I think the offending patches should be reverted, but unfortunately they
may no longer revert cleanly since there were some new features (e.g.
runtime pm) thrown in the mix.

Johan