Re: potential-null-pointer-dereference-in-amiga-serial-driver.patch added to -mm tree

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

Hi Alexey,

On Tue, May 31, 2005 at 07:49:15PM +0400, Alexey Dobriyan wrote:
> On Tuesday 31 May 2005 13:08, akpm@osdl.org wrote:
> > A pointer is dereferenced before it is null-checked.
> 
> > --- 25/drivers/char/amiserial.c~potential-null-pointer-dereference-in-amiga-serial-driver
> > +++ 25-akpm/drivers/char/amiserial.c
> 
> >  static void rs_put_char(struct tty_struct *tty, unsigned char ch)
> >  {
> > -	struct async_struct *info = (struct async_struct *)tty->driver_data;
> > +	struct async_struct *info;
> >  	unsigned long flags;
> >  
> > +	if (!tty)
> > +		return;
> 
> Can ->put_char be ever called with tty being NULL? From my reading of
> drivers/char/n_tty.c it can't.

Nope it can't, but the change makes the code more readable IMO, while handling
a NULL "tty" argument properly (which the old version pretends to, but doesnt).

> Every single time ->put_char is used a-la
> 
> 	tty->driver->put_char(tty, '\r');
> 
> So, tty will be dereferenced before function call. Same for static inline
> put_char() there.