On 2020/07/15 20:17, Tetsuo Handa wrote:
On 2020/07/15 18:48, Dan Carpenter wrote:
@@ -216,7 +216,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info, region.color = color; region.rop = ROP_COPY;
- if (rw && !bottom_only) {
- if ((int) rw > 0 && !bottom_only) { region.dx = info->var.xoffset + rs;
^^^^^^^^^^^^^^^^^^^^^^If you choose a very high positive "rw" then this addition can overflow. info->var.xoffset comes from the user and I don't think it's checked...
Well, I think it would be checked by "struct fb_ops"->check_var hook. For example, vmw_fb_check_var() has
if ((var->xoffset + var->xres) > par->max_width || (var->yoffset + var->yres) > par->max_height) { DRM_ERROR("Requested geom can not fit in framebuffer\n"); return -EINVAL; }
check. Of course, there might be integer overflow in that check... Having sanity check at caller of "struct fb_ops"->check_var might be nice.
Well, while
const int fd = open("/dev/fb0", O_ACCMODE); struct fb_var_screeninfo var = { }; ioctl(fd, FBIOGET_VSCREENINFO, &var); var.xres = var.yres = 4; var.xoffset = 4294967292U; ioctl(fd, FBIOPUT_VSCREENINFO, &var);
bypassed
(var->xoffset + var->xres) > par->max_width
check in vmw_fb_check_var(),
---------- --- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -216,6 +216,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info, region.color = color; region.rop = ROP_COPY;
+ printk(KERN_INFO "%s info->var.xoffset=%u rs=%u info->var.yoffset=%u bs=%u\n", __func__, info->var.xoffset, rs, info->var.yoffset, bs); if ((int) rw > 0 && !bottom_only) { region.dx = info->var.xoffset + rs; region.dy = 0; ----------
says that info->var.xoffset does not come from the user.
---------- bit_clear_margins info->var.xoffset=0 rs=1024 info->var.yoffset=0 bs=800 ----------