Re: [PATCH RFC] tty: Fix out-of-bound vmalloc access in imageblit

[Igor Torrente]

Hi Greg,

On 5/31/21 10:18 AM, Greg KH wrote:
> On Mon, May 31, 2021 at 09:47:13AM -0300, Igor Matheus Andrade Torrente wrote:
> > This issue happens when a userspace program does an ioctl
> > FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct
> > containing only the fields xres, yres, and bits_per_pixel
> > with values.
> >
> > If this struct is the same as the previous ioctl, the
> > vc_resize() detects it and doesn't call the resize_screen(),
> > leaving the fb_var_screeninfo incomplete. And this leads to
> > the updatescrollmode() calculates a wrong value to
> > fbcon_display->vrows, which makes the real_y() return a
> > wrong value of y, and that value, eventually, causes
> > the imageblit to access an out-of-bound address value.
> >
> > To solve this issue I brougth the resize_screen() the
> > beginning of vc_do_resize(), so it will "fix and fill"
> > the fb_var_screeninfo even if the screen does not need any
> > resizing.
> >
> > Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@xxxxxxxxx>
> > ---
> >   drivers/tty/vt/vt.c | 12 ++++--------
> >   1 file changed, 4 insertions(+), 8 deletions(-)
>
> Why is this "RFC"?

Maybe I'm using it wrongly, but I usually use RFC to indicate that patch 
is probably not ready and needs comments/suggestions to improve it. In 
case, I don't have much experience with vt driver and I'm a little bit 
afraid to break something.