CVE-2023-53075

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

ftrace: Fix invalid address access in lookup_rec() when index is 0

KASAN reported follow problem:

BUG: KASAN: use-after-free in lookuprec Read of size 8 at addr ffff000199270ff0 by task modprobe CPU: 2 Comm: modprobe Call trace: kasanreport __asanload8 lookuprec ftracelocation archcheckftracelocation checkkprobeaddresssafe registerkprobe

When checking pg->records[pg->index - 1].ip in lookuprec(), it can get a pg which is newly added to ftracepagesstart in ftraceprocess_locs(). Before the first pg->index++, index is 0 and accessing pg->records[-1].ip will cause this problem.

Don't check the ip when pg->index is 0.