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

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