Re: [PATCH] Fix memory leak in vc_resize/vc_allocate

["Antonino A. Daplas" <adaplas@pol.net>]

On Mon, 2006-08-14 at 15:43 -0700, Andrew Morton wrote:
> On Thu, 10 Aug 2006 15:22:21 +0100
> Catalin Marinas <catalin.marinas@arm.com> wrote:
> 
> > From: Catalin Marinas <catalin.marinas@arm.com>
> > 
> > Memory leaks can happen in the vc_resize() function in drivers/char/vt.c
> > because of the vc->vc_screenbuf variable overriding in vc_allocate(). The
> > kmemleak reported trace is as follows:
> > 
> >   <__kmalloc>
> >   <vc_resize>
> >   <fbcon_init>
> >   <visual_init>
> >   <vc_allocate>
> >   <con_open>
> >   <tty_open>
> >   <chrdev_open>
> > 
> > This patch no longer allocates a screen buffer in vc_allocate() if it was
> > already allocated by vc_resize().
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > ---
> > 
> >  drivers/char/vt.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/char/vt.c b/drivers/char/vt.c
> > index da7e66a..31c8b32 100644
> > --- a/drivers/char/vt.c
> > +++ b/drivers/char/vt.c
> > @@ -730,7 +730,8 @@ int vc_allocate(unsigned int currcons)	/
> >  	    visual_init(vc, currcons, 1);
> >  	    if (!*vc->vc_uni_pagedir_loc)
> >  		con_set_default_unimap(vc);
> > -	    vc->vc_screenbuf = kmalloc(vc->vc_screenbuf_size, GFP_KERNEL);
> > +	    if (!vc->vc_kmalloced)
> > +		vc->vc_screenbuf = kmalloc(vc->vc_screenbuf_size, GFP_KERNEL);
> >  	    if (!vc->vc_screenbuf) {
> >  		kfree(vc);
> >  		vc_cons[currcons].d = NULL;
> 
> hm.  Maybe.  I'd worry that the memory at vc->vc_screenbuf isn't of the
> correct size and this patch will convert a leak into a buffer overrun.

It's a safe test, visual_init() will assure that screenbuf_size will
always be correct. 

> Also, what's up with this, in vc_resize()?
> 
> 	if (vc->vc_kmalloced)
> 		kfree(vc->vc_screenbuf);
> 	vc->vc_screenbuf = newscreen;
> 	vc->vc_kmalloced = 1;
> 
> if vc->vc_kmalloced means "there is kmalloced memory at vc->vc_screenbuf"
> then this is wrong.

vc_screenbuf is either of the bootmem type or the kmalloced type as
indicated by vc->vc_kmalloced.

> 
> This code is all pretty twisty and I fear touching it.

Yes, but the patch as is should be okay.

Tony