On Wed, Aug 26, 2020 at 12:16:59AM +0800, yanfei.xu@xxxxxxxxxxxxx wrote:
> From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
>
> When using systemcall to read the rawdescriptors, make sure we won't
> access to the rawdescriptors never allocated, which are number
> exceed the USB_MAXCONFIG.
>
> Reported-by: syzbot+256e56ddde8b8957eabd@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
> ---
> drivers/usb/core/sysfs.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
> index a2ca38e25e0c..1a7a625e5f55 100644
> --- a/drivers/usb/core/sysfs.c
> +++ b/drivers/usb/core/sysfs.c
> @@ -895,7 +895,8 @@ read_descriptors(struct file *filp, struct kobject *kobj,
> * configurations (config plus subsidiary descriptors).
> */
> for (cfgno = -1; cfgno < udev->descriptor.bNumConfigurations &&
> - nleft > 0; ++cfgno) {
> + nleft > 0 &&
> + cfgno < USB_MAXCONFIG; ++cfgno) {
> if (cfgno < 0) {
> src = &udev->descriptor;
> srclen = sizeof(struct usb_device_descriptor);
This is not the right way to fix the problem.
Instead, we should make sure that udev->descriptor.bNumConfigurations is
always <= USB_MAXCONFIG. That's what this code in
usb_get_configuration() is supposed to do:
int ncfg = dev->descriptor.bNumConfigurations;
...
if (ncfg > USB_MAXCONFIG) {
dev_warn(ddev, "too many configurations: %d, "
"using maximum allowed: %d\n", ncfg, USB_MAXCONFIG);
dev->descriptor.bNumConfigurations = ncfg = USB_MAXCONFIG;
}
If you want to fix the bug, you need to figure out why this isn't
working.
Alan Stern
