Local service interruption via request-statistic overflow

Divide by zero in the Linux kernel block layer from 4.15 allows local users to crash the system through request-statistic overflow. blk_rq_stat_sum() adds dst->nr_samples and src->nr_samples without detecting unsigned wraparound, then uses the zero result as a divisor while merging block request statistics. Exploitation requires local low-privilege access and enough statistic samples to wrap the counter; the reported consequence is a kernel crash, not data disclosure or modification.