On Sat, Jun 08, 2019 at 06:22:19PM +0200, Greg KH wrote:
> On Sun, Jun 09, 2019 at 12:01:38AM +0800, Gen Zhang wrote:
> > On Tue, May 28, 2019 at 08:45:29AM +0800, Gen Zhang wrote:
> > > In function con_init(), the pointer variable vc_cons[currcons].d, vc and
> > > vc->vc_screenbuf is allocated by kzalloc(). And they are used in the
> > > following codes. However, kzalloc() returns NULL when fails, and null
> > > pointer dereference may happen. And it will cause the kernel to crash.
> > > Therefore, we should check the return value and handle the error.
> > >
> > > Further, since the allcoation is in a loop, we should free all the
> > > allocated memory in a loop.
> > >
> > > Signed-off-by: Gen Zhang <blackgod016...@gmail.com>
> > > Reviewed-by: Nicolas Pitre <n...@fluxnic.net>
> > > ---
> > > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> > > index fdd12f8..d50f68f 100644
> > > --- a/drivers/tty/vt/vt.c
> > > +++ b/drivers/tty/vt/vt.c
> > > @@ -3350,10 +3350,14 @@ static int __init con_init(void)
> > >
> > > for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
> > > vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data),
> > > GFP_NOWAIT);
> > > + if (!vc)
> > > + goto fail1;
> > > INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
> > > tty_port_init(&vc->port);
> > > visual_init(vc, currcons, 1);
> > > vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
> > > + if (!vc->vc_screenbuf)
> > > + goto fail2;
> > > vc_init(vc, vc->vc_rows, vc->vc_cols,
> > > currcons || !vc->vc_sw->con_save_screen);
> > > }
> > > @@ -3375,6 +3379,16 @@ static int __init con_init(void)
> > > register_console(&vt_console_driver);
> > > #endif
> > > return 0;
> > > +fail1:
> > > + while (currcons > 0) {
> > > + currcons--;
> > > + kfree(vc_cons[currcons].d->vc_screenbuf);
> > > +fail2:
> > > + kfree(vc_cons[currcons].d);
> > > + vc_cons[currcons].d = NULL;
> > > + }
>
> Wait, will that even work? You can jump into the middle of a while
> loop?
I felt like the same when I saw reviewer's advice to write in this way.
But I tested, and it did work.
>
> Ugh, that's beyond ugly. And please provide "real" names for the
> labels, "fail1" and "fail2" do not tell anything here.
Sure, I can revise that if needed.
Thanks
Gen
>
> Also, have you actually be able to trigger this?
>
> thanks,
>
> greg k-h
