[PATCH] vgacon: fix out of bounds write to the scrollback buffer

[张云海]

On 2020/7/29 16:11, Jiri Slaby wrote:
> But the loop checks for the overflow:
>   if (vgacon_scrollback_cur->tail >= vgacon_scrollback_cur->size)
>         vgacon_scrollback_cur->tail = 0;
> 
> So the first 2 iterations would write to the end of the buffer and this
> 3rd one should have zeroed ->tail.

In the 2nd  iteration before the check:
vgacon_scrollback_cur->tail is 65360 which is still less then
vgacon_scrollback_cur->size(65440), so the ->tail won't be zeroed.

Then it gose to the 3rd  iteration, overflow occurs.

Regards,
Yunhai Zhang / NSFOCUS Security Team