CVE-2026-72117: can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()

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

can: bcm: fix data race on rxstamp/rxifindex in bcmrxhandler()

For an rx op subscribed on all interfaces (ifindex == 0), the same op is registered once in the shared per-netns wildcard filter list, so bcmrxhandler() can run concurrently on different CPUs for frames arriving on different net devices.

op->rxstamp and op->rxifindex were written before bcmrxupdatelock was taken, allowing concurrent writers to race each other - including a torn store of the 64-bit rxstamp on 32-bit platforms.

Beyond a torn store bcmsendtouser() must report the timestamp/ifindex of the very same frame whose content it is delivering. So the assignment is placed in the same unbroken bcmrxupdatelock section as the content comparison.

As a side effect, the RTR-request frame feature (which never reach bcmsendtouser()) no longer updates rxstamp/rxifindex, since only the notification path needs them.