CVE-2026-43210: tracing: ring-buffer: Fix to check event length before using

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

tracing: ring-buffer: Fix to check event length before using

Check the event length before adding it for accessing next index in rbreaddatabuffer(). Since this function is used for validating possibly broken ring buffers, the length of the event could be broken. In that case, the new event (e + len) can point a wrong address. To avoid invalid memory access at boot, check whether the length of each event is in the possible range before using it.