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

Vulnerability Description

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 lookup_rec Read of size 8 at addr ffff000199270ff0 by task modprobe CPU: 2 Comm: modprobe Call trace: kasan_report __asan_load8 lookup_rec ftrace_location arch_check_ftrace_location check_kprobe_address_safe register_kprobe When checking pg->records[pg->index - 1].ip in lookup_rec(), it can get a pg which is newly added to ftrace_pages_start in ftrace_process_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.

References

• https://git.kernel.org/stable/c/2de28e5ce34b22b73b833a21e2c45ae3aade3964
• https://git.kernel.org/stable/c/7569ee04b0e3b32df79f64db3a7138573edad9bc
• https://git.kernel.org/stable/c/ac58b88ccbbb8e9fb83e137cee04a856b1ea6635
• https://git.kernel.org/stable/c/83c3b2f4e7c61367c7b24551f4c6eb94bbdda283
• https://git.kernel.org/stable/c/2a0d71fabfeb349216d33f001a6421b1768bd3a9
• https://git.kernel.org/stable/c/4f84f31f63416b0f02fc146ffdc4ab32723eb7e8
• https://git.kernel.org/stable/c/f1bd8b7fd890d87d0dc4dedc6287ea34dd07c0b4
• https://git.kernel.org/stable/c/ee92fa443358f4fc0017c1d0d325c27b37802504