On Fri, Jul 10, 2020 at 08:31:42PM +0900, Tetsuo Handa wrote:
> On 2020/07/10 19:55, Greg Kroah-Hartman wrote:
> >> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> >> index 48a8199f7845..8497e9206607 100644
> >> --- a/drivers/tty/vt/vt.c
> >> +++ b/drivers/tty/vt/vt.c
> >> @@ -1126,7 +1126,7 @@ int vc_allocate(unsigned int currcons) /*
> >> return 0 on success */
> >> con_set_default_unimap(vc);
> >>
> >> vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_KERNEL);
> >> - if (!vc->vc_screenbuf)
> >> + if (ZERO_OR_NULL_PTR(vc->vc_screenbuf))
> >
> > No, let's check this before we do kzalloc() please, that's just an odd
> > way of doing an allocation we shouldn't have had to do.
>
> OK. I can change to
>
> + if (vc->vc_screenbuf_size > KMALLOC_MAX_SIZE || !vc->vc_screenbuf_size)
> + goto err_free;
> vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_KERNEL);
> if (!vc->vc_screenbuf)
> goto err_free;
>
> like vc_do_resize() does. But I'm currently waiting for syzbot to test this
> patch, for
> I don't have an environment for reproducing this problem.
That looks much more sane, thanks.
>
> >
> >> goto err_free;
> >>
> >> /* If no drivers have overridden us and the user didn't pass a
> >> @@ -1212,7 +1212,7 @@ static int vc_do_resize(struct tty_struct *tty,
> >> struct vc_data *vc,
> >> if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
> >> return 0;
> >>
> >> - if (new_screen_size > KMALLOC_MAX_SIZE)
> >> + if (new_screen_size > KMALLOC_MAX_SIZE || !new_screen_size)
> >> return -EINVAL;
> >> newscreen = kzalloc(new_screen_size, GFP_USER);
> >> if (!newscreen)
> >> @@ -3393,6 +3393,7 @@ static int __init con_init(void)
> >> INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
> >> tty_port_init(&vc->port);
> >> visual_init(vc, currcons, 1);
> >> + /* Assuming vc->vc_screenbuf_size is sane here, for this is
> >> __init code. */
> >
> > Shouldn't we also check this here, or before we get here, too?
>
> This is an __init function. Can we somehow pass column=0 or row=0 ?
You could, it's much less likely, but why not catch this if you can?
> > Just checking the values and rejecting that as a valid screen size
> > should be sufficient.
>
> Hmm, where are we checking that column * row does not exceed UINT_MAX, given
> that
> "struct vc_data"->vc_{cols,rows,screenbuf_size} are "unsigned int" and we do
>
> vc->vc_size_row = vc->vc_cols << 1;
> vc->vc_screenbuf_size = vc->vc_rows * vc->vc_size_row;
>
> in visual_init() ? Don't we need to reject earlier?
Probably, it's some twisty code :(
