kprobes: avoid crash when rmmod/insmod after ftrace killed

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

kprobes: avoid crash when rmmod/insmod after ftrace killed

After we hit ftrace is killed by some errors, the kernel crash if

we remove modules in which kprobe probes.

BUG: unable to handle page fault for address: fffffbfff805000d

PGD 817fcc067 P4D 817fcc067 PUD 817fc8067 PMD 101555067 PTE 0

Oops: Oops: 0000 [#1] SMP KASAN PTI

CPU: 4 UID: 0 PID: 2012 Comm: rmmod Tainted: G W OE

Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE

RIP: 0010:kprobes_module_callback+0x89/0x790

RSP: 0018:ffff88812e157d30 EFLAGS: 00010a02

RAX: 1ffffffff805000d RBX: dffffc0000000000 RCX: ffffffff86a8de90

RDX: ffffed1025c2af9b RSI: 0000000000000008 RDI: ffffffffc0280068

RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed1025c2af9a

R10: ffff88812e157cd7 R11: 205d323130325420 R12: 0000000000000002

R13: ffffffffc0290488 R14: 0000000000000002 R15: ffffffffc0280040

FS: 00007fbc450dd740(0000) GS:ffff888420331000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: fffffbfff805000d CR3: 000000010f624000 CR4: 00000000000006f0

Call Trace:

<TASK>

notifier_call_chain+0xc6/0x280

blocking_notifier_call_chain+0x60/0x90

__do_sys_delete_module.constprop.0+0x32a/0x4e0

do_syscall_64+0x5d/0xfa0

entry_SYSCALL_64_after_hwframe+0x76/0x7e

This is because the kprobe on ftrace does not correctly handles

the kprobe_ftrace_disabled flag set by ftrace_kill().

To prevent this error, check kprobe_ftrace_disabled in

__disarm_kprobe_ftrace() and skip all ftrace related operations.