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
----------
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