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

Hi,

On 29. 07. 20, 9:53, 张云海 wrote:

This patch dosen't fix the issue, the check should be in the loop.

The change of the VT sze is before vgacon_scrollback_update, not in the
meantime.

Let's consider the following situation:
	suppose:
		vgacon_scrollback_cur->size is 65440
		vgacon_scrollback_cur->tail is 64960
		c->vc_size_row is 160
		count is 5
	
	Reset c->vc_size_row to 200 by VT_RESIZE, then call
vgacon_scrollback_update.
	
	This will pass the check, since (vgacon_scrollback_cur->tail +
c->vc_size_row)
	is 65160 which is less then vgacon_scrollback_cur->size(65440).

	However, in the 3rd iteration of the loop, vgacon_scrollback_cur->tail
is update
	to 65360, the memcpy will overflow.

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.

thanks,
-- 
js
suse labs