On Mon, Feb 07, 2022 at 12:50:41PM +0100, Hans Verkuil wrote:
> Hi Dan,
>
> On 2/7/22 12:34, Dan Carpenter wrote:
> > [ This code is older, but it showed up as a new warning because of
> > moving the files around - dan ]
> >
> > Hello Hans Verkuil,
> >
> > The patch 71c689dc2e73: "media: v4l2-ctrls: split up into four source
> > files" from Apr 27, 2021, leads to the following Smatch static
> > checker warning:
> >
> > drivers/media/v4l2-core/v4l2-ctrls-api.c:374 v4l2_g_ext_ctrls_common() warn: uncapped user size for kvmalloc() will WARN
> > drivers/media/v4l2-core/v4l2-ctrls-api.c:545 try_set_ext_ctrls_common() warn: uncapped user size for kvmalloc() will WARN
> >
> > drivers/media/v4l2-core/v4l2-ctrls-api.c
> > 351 int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
> > 352 struct v4l2_ext_controls *cs,
> > 353 struct video_device *vdev)
> > 354 {
> > 355 struct v4l2_ctrl_helper helper[4];
> > 356 struct v4l2_ctrl_helper *helpers = helper;
> > 357 int ret;
> > 358 int i, j;
> > 359 bool is_default, is_request;
> > 360
> > 361 is_default = (cs->which == V4L2_CTRL_WHICH_DEF_VAL);
> > 362 is_request = (cs->which == V4L2_CTRL_WHICH_REQUEST_VAL);
> > 363
> > 364 cs->error_idx = cs->count;
> > 365 cs->which = V4L2_CTRL_ID2WHICH(cs->which);
> > 366
> > 367 if (!hdl)
> > 368 return -EINVAL;
> > 369
> > 370 if (cs->count == 0)
> > 371 return class_check(hdl, cs->which);
> > 372
> > 373 if (cs->count > ARRAY_SIZE(helper)) {
> > --> 374 helpers = kvmalloc_array(cs->count, sizeof(helper[0]),
> >
> > These days if "cs->count" is larger than INT_MAX it will trigger a
> > WARN() because basically "people shouldn't be so trusting of user
> > space". kvmalloc() used to be able to allocate more than INT_MAX but
> > that led to integer overflow problmes and security bugs.
> >
> > This "cs->count" value comes from the user via the ioctl. I don't know
> > what a sensible upper bound is though.
>
> cs->count is capped to 1024 in drivers/media/v4l2-core/v4l2-ioctl.c.
> Search for V4L2_CID_MAX_CTRLS.
>
> There is no way for smatch to know this of course.
Yeah. It's tricky. The switch statement in check_array_args() is too
much data for Smatch and the void *arg confuses Smatch as well. :/
Thanks for looking at this.
regards,
dan carpenter
