Re: Text mode VGA-console scrolling is broken in upstream & stable trees

On 30. 07. 25, 16:06, Jari Ruusu wrote:

The patch that broke text mode VGA-console scrolling is this one: "vgacon: Add check for vc_origin address range in vgacon_scroll()" commit 864f9963ec6b4b76d104d595ba28110b87158003 upstream.

How to preproduce: (1) boot a kernel that is configured to use text mode VGA-console (2) type commands: ls -l /usr/bin | less -S (3) scroll up/down with cursor-down/up keys

Above mentioned patch seems to have landed in upstream and all kernel.org stable trees with zero testing. Even minimal testing would have shown that it breaks text mode VGA-console scrolling.

At the time this was posted (privately and on security@), I commented:

=====

--- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -1168,7 +1168,7 @@ static bool vgacon_scroll(struct vc_data *c,

unsigned int t, unsigned int b,

                               c->vc_screenbuf_size - delta);
                  c->vc_origin = vga_vram_end - c->vc_screenbuf_size;
                  vga_rolled_over = 0;

•         } else
  

•         } else if (oldo - delta >= (unsigned long)c->vc_screenbuf)
                  c->vc_origin -= delta;
  

IMO you should also add: else c->vc_origin = c->vc_screenbuf;

Or clamp 'delta' beforehand and don't add the 'if'.

=====

That did not happen, AFAICS. Care to test the above suggestion?

thanks,