linux-kernel - Re: [PATCH 1/2] tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth

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Date:   Sat, 12 Nov 2022 15:12:17 -0600
From:   Tom Zanussi <zanussi@...nel.org>
To:     Shang XiaoJing <shangxiaojing@...wei.com>, rostedt@...dmis.org,
        mhiramat@...nel.org, fengguang.wu@...el.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] tracing: Fix memory leak in test_gen_synth_cmd()
 and test_empty_synth_event()

Hi Shang,

Thanks for finding this bug, comment below...

On Tue, 2022-11-08 at 16:31 +0800, Shang XiaoJing wrote:
> test_gen_synth_cmd() only free buf in fail path, hence buf will leak
> when there is no failure. Add kfree(buf) to prevent the memleak. The
> same reason and solution in test_empty_synth_event().
> 
> unreferenced object 0xffff8881127de000 (size 2048):
>   comm "modprobe", pid 247, jiffies 4294972316 (age 78.756s)
>   hex dump (first 32 bytes):
>     20 67 65 6e 5f 73 79 6e 74 68 5f 74 65 73 74 20   gen_synth_test
>     20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69 64 5f   pid_t next_pid_
>   backtrace:
>     [<000000004254801a>] kmalloc_trace+0x26/0x100
>     [<0000000039eb1cf5>] 0xffffffffa00083cd
>     [<000000000e8c3bc8>] 0xffffffffa00086ba
>     [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
>     [<00000000aa189e6d>] do_init_module+0x1cf/0x680
>     [<00000000d513222b>] load_module+0x6a50/0x70a0
>     [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
>     [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
>     [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> unreferenced object 0xffff8881127df000 (size 2048):
>   comm "modprobe", pid 247, jiffies 4294972324 (age 78.728s)
>   hex dump (first 32 bytes):
>     20 65 6d 70 74 79 5f 73 79 6e 74 68 5f 74 65 73   empty_synth_tes
>     74 20 20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69  t  pid_t next_pi
>   backtrace:
>     [<000000004254801a>] kmalloc_trace+0x26/0x100
>     [<00000000d4db9a3d>] 0xffffffffa0008071
>     [<00000000c31354a5>] 0xffffffffa00086ce
>     [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
>     [<00000000aa189e6d>] do_init_module+0x1cf/0x680
>     [<00000000d513222b>] load_module+0x6a50/0x70a0
>     [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
>     [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
>     [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Fixes: 9fe41efaca08 ("tracing: Add synth event generation test
> module")
> Signed-off-by: Shang XiaoJing <shangxiaojing@...wei.com>
> ---
>  kernel/trace/synth_event_gen_test.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/synth_event_gen_test.c
> b/kernel/trace/synth_event_gen_test.c
> index 0b15e975d2c2..db1ec4809ad1 100644
> --- a/kernel/trace/synth_event_gen_test.c
> +++ b/kernel/trace/synth_event_gen_test.c
> @@ -120,6 +120,7 @@ static int __init test_gen_synth_cmd(void)
>  
>         /* Now generate a gen_synth_test event */
>         ret = synth_event_trace_array(gen_synth_test, vals,
> ARRAY_SIZE(vals));
> +       kfree(buf);
>   out:
>         return ret;
>   delete:
> @@ -227,6 +228,7 @@ static int __init test_empty_synth_event(void)
>  
>         /* Now trace an empty_synth_test event */
>         ret = synth_event_trace_array(empty_synth_test, vals,
> ARRAY_SIZE(vals));
> +       kfree(buf);
>   out:
>         return ret;
>   delete:

Makes sense, and if you do this then you could probably remove the
other kfree() at the bottom and clean the code up a bit, like change
this:

       /* Now generate a gen_synth_test event */
       ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
       kfree(buf);
 out:
        return ret;
 delete:
        /* We got an error after creating the event, delete it */
	synth_event_delete("gen_synth_test");
 free:
        kfree(buf);

	goto out;
}

to this:

       /* Now generate a gen_synth_test event */
       ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
 free:
       kfree(buf);
       return ret;
 delete:
        /* We got an error after creating the event, delete it */
	synth_event_delete("gen_synth_test");
 	goto free;
}

What do you think?

Tom