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

Link: https://lore.kernel.org/all/20221108015130.28326-2-shangxiaojing@huawei.com/

Fixes: 64836248 ("tracing: Add kprobe event command generation test module")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

kernel/trace/kprobe_event_gen_test.c

@@ -73,6 +73,10 @@ static struct trace_event_file *gen_kretprobe_test;
 #define KPROBE_GEN_TEST_ARG3	NULL
 #endif
 
+static bool trace_event_file_is_valid(struct trace_event_file *input)
+{
+	return input && !IS_ERR(input);
+}
 
 /*
  * Test to make sure we can create a kprobe event, then add more
@@ -217,10 +221,12 @@ static int __init kprobe_event_gen_test_init(void)
 
 	ret = test_gen_kretprobe_cmd();
 	if (ret) {
+		if (trace_event_file_is_valid(gen_kretprobe_test)) {
 			WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
 							  "kprobes",
 							  "gen_kretprobe_test", false));
 			trace_put_event_file(gen_kretprobe_test);
+		}
 		WARN_ON(kprobe_event_delete("gen_kretprobe_test"));
 	}
 
@@ -229,6 +235,7 @@ static int __init kprobe_event_gen_test_init(void)
 
 static void __exit kprobe_event_gen_test_exit(void)
 {
+	if (trace_event_file_is_valid(gen_kprobe_test)) {
 		/* Disable the event or you can't remove it */
 		WARN_ON(trace_array_set_clr_event(gen_kprobe_test->tr,
 						  "kprobes",
@@ -236,10 +243,13 @@ static void __exit kprobe_event_gen_test_exit(void)
 
 		/* Now give the file and instance back */
 		trace_put_event_file(gen_kprobe_test);
+	}
+
 
 	/* Now unregister and free the event */
 	WARN_ON(kprobe_event_delete("gen_kprobe_test"));
 
+	if (trace_event_file_is_valid(gen_kretprobe_test)) {
 		/* Disable the event or you can't remove it */
 		WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
 						  "kprobes",
@@ -247,6 +257,8 @@ static void __exit kprobe_event_gen_test_exit(void)
 
 		/* Now give the file and instance back */
 		trace_put_event_file(gen_kretprobe_test);
+	}
+
 
 	/* Now unregister and free the event */
 	WARN_ON(kprobe_event_delete("gen_kretprobe_test"));