tracing: kprobe: Fix memory leak in test_gen_kprobe/kretprobe_cmd()

test_gen_kprobe_cmd() only free buf in fail path, hence buf will leak
when there is no failure. Move kfree(buf) from fail path to common path
to prevent the memleak. The same reason and solution in
test_gen_kretprobe_cmd().

unreferenced object 0xffff888143b14000 (size 2048):
  comm "insmod", pid 52490, jiffies 4301890980 (age 40.553s)
  hex dump (first 32 bytes):
    70 3a 6b 70 72 6f 62 65 73 2f 67 65 6e 5f 6b 70  p:kprobes/gen_kp
    72 6f 62 65 5f 74 65 73 74 20 64 6f 5f 73 79 73  robe_test do_sys
  backtrace:
    [<000000006d7b836b>] kmalloc_trace+0x27/0xa0
    [<0000000009528b5b>] 0xffffffffa059006f
    [<000000008408b580>] do_one_initcall+0x87/0x2a0
    [<00000000c4980a7e>] do_init_module+0xdf/0x320
    [<00000000d775aad0>] load_module+0x3006/0x3390
    [<00000000e9a74b80>] __do_sys_finit_module+0x113/0x1b0
    [<000000003726480d>] do_syscall_64+0x35/0x80
    [<000000003441e93b>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

Link: https://lore.kernel.org/all/[email protected]/

Fixes: 6483624 ("tracing: Add kprobe event command generation test module")
Cc: [email protected]
Signed-off-by: Shang XiaoJing <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>

Author: Shang XiaoJing

kernel/trace/kprobe_event_gen_test.c

@@ -100,20 +100,20 @@ static int __init test_gen_kprobe_cmd(void)
 					 KPROBE_GEN_TEST_FUNC,
 					 KPROBE_GEN_TEST_ARG0, KPROBE_GEN_TEST_ARG1);
 	if (ret)
-		goto free;
+		goto out;
 
 	/* Use kprobe_event_add_fields to add the rest of the fields */
 
 	ret = kprobe_event_add_fields(&cmd, KPROBE_GEN_TEST_ARG2, KPROBE_GEN_TEST_ARG3);
 	if (ret)
-		goto free;
+		goto out;
 
 	/*
 	 * This actually creates the event.
 	 */
 	ret = kprobe_event_gen_cmd_end(&cmd);
 	if (ret)
-		goto free;
+		goto out;
 
 	/*
 	 * Now get the gen_kprobe_test event file.  We need to prevent
@@ -136,13 +136,11 @@ static int __init test_gen_kprobe_cmd(void)
 		goto delete;
 	}
  out:
+	kfree(buf);
 	return ret;
  delete:
 	/* We got an error after creating the event, delete it */
 	ret = kprobe_event_delete("gen_kprobe_test");
- free:
-	kfree(buf);
-
 	goto out;
 }
 
@@ -170,14 +168,14 @@ static int __init test_gen_kretprobe_cmd(void)
 					    KPROBE_GEN_TEST_FUNC,
 					    "$retval");
 	if (ret)
-		goto free;
+		goto out;
 
 	/*
 	 * This actually creates the event.
 	 */
 	ret = kretprobe_event_gen_cmd_end(&cmd);
 	if (ret)
-		goto free;
+		goto out;
 
 	/*
 	 * Now get the gen_kretprobe_test event file.  We need to
@@ -201,13 +199,11 @@ static int __init test_gen_kretprobe_cmd(void)
 		goto delete;
 	}
  out:
+	kfree(buf);
 	return ret;
  delete:
 	/* We got an error after creating the event, delete it */
 	ret = kprobe_event_delete("gen_kretprobe_test");
- free:
-	kfree(buf);
-
 	goto out;
 }