tracing: kprobe: Fix potential null-ptr-deref on trace_event_file in kprobe_event_gen_test_exit()

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

tracing: kprobe: Fix potential null-ptr-deref on trace_event_file in kprobe_event_gen_test_exit()

When trace_get_event_file() failed, gen_kretprobe_test will be assigned

as the error code. If module kprobe_event_gen_test is removed now, the

null pointer dereference will happen in kprobe_event_gen_test_exit().

Check if gen_kprobe_test or gen_kretprobe_test is error code or NULL

before dereference them.

BUG: kernel NULL pointer dereference, address: 0000000000000012

PGD 0 P4D 0

Oops: 0000 [#1] SMP PTI

CPU: 3 PID: 2210 Comm: modprobe Not tainted

6.1.0-rc1-00171-g2159299a3b74-dirty #217

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS

rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014

RIP: 0010:kprobe_event_gen_test_exit+0x1c/0xb5 [kprobe_event_gen_test]

Code: Unable to access opcode bytes at 0xffffffff9ffffff2.

RSP: 0018:ffffc900015bfeb8 EFLAGS: 00010246

RAX: ffffffffffffffea RBX: ffffffffa0002080 RCX: 0000000000000000

RDX: ffffffffa0001054 RSI: ffffffffa0001064 RDI: ffffffffdfc6349c

RBP: ffffffffa0000000 R08: 0000000000000004 R09: 00000000001e95c0

R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000800

R13: ffffffffa0002420 R14: 0000000000000000 R15: 0000000000000000

FS: 00007f56b75be540(0000) GS:ffff88813bc00000(0000)

knlGS:0000000000000000

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

CR2: ffffffff9ffffff2 CR3: 000000010874a006 CR4: 0000000000330ee0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

<TASK>

__x64_sys_delete_module+0x206/0x380

? lockdep_hardirqs_on_prepare+0xd8/0x190

? syscall_enter_from_user_mode+0x1c/0x50

do_syscall_64+0x3f/0x90

entry_SYSCALL_64_after_hwframe+0x63/0xcd