usb: dwc3: gadget: check that event count does not exceed event buffer length

In the Linux kernel, the following vulnerability has been resolved:

usb: dwc3: gadget: check that event count does not exceed event buffer length

The event count is read from register DWC3_GEVNTCOUNT.

There is a check for the count being zero, but not for exceeding the

event buffer length.

Check that event count does not exceed event buffer length,

avoiding an out-of-bounds access when memcpy'ing the event.

Crash log:

Unable to handle kernel paging request at virtual address ffffffc0129be000

pc : __memcpy+0x114/0x180

lr : dwc3_check_event_buf+0xec/0x348

x3 : 0000000000000030 x2 : 000000000000dfc4

x1 : ffffffc0129be000 x0 : ffffff87aad60080

Call trace:

__memcpy+0x114/0x180

dwc3_interrupt+0x24/0x34