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From: Steven Rostedt <rostedt@goodmis.org>
To: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Shuah Khan <shuah@kernel.org>,
	Hiraku Toyooka <hiraku.toyooka@cybertrust.co.jp>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 1/3] [BUGFIX] tracing: Fix double free of event_trigger_data
Date: Tue, 24 Jul 2018 17:30:08 -0400
Message-ID: <20180724173008.454cdf10@gandalf.local.home> (raw)
In-Reply-To: <20180724164959.3cbc1422@gandalf.local.home>

On Tue, 24 Jul 2018 16:49:59 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> > Hmm it seems we should review the register_trigger() implementation.
> > It should return the return value of trace_event_trigger_enable_disable(),
> > shouldn't it?
> >  
> 
> Yeah, that's not done well. I'll fix it up.
> 
> Thanks for pointing it out.

Tom,

register_trigger() is messed up. I should have caught this when it was
first submitted, but I'm totally confused. The comments don't match the
code.

First we have this:

	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
	/*
	 * The above returns on success the # of functions enabled,
	 * but if it didn't find any functions it returns zero.
	 * Consider no functions a failure too.
	 */

Which looks to be total BS.

As we have this:

/**
 * register_trigger - Generic event_command @reg implementation
 * @glob: The raw string used to register the trigger
 * @ops: The trigger ops associated with the trigger
 * @data: Trigger-specific data to associate with the trigger
 * @file: The trace_event_file associated with the event
 *
 * Common implementation for event trigger registration.
 *
 * Usually used directly as the @reg method in event command
 * implementations.
 *
 * Return: 0 on success, errno otherwise
 */
static int register_trigger(char *glob, struct event_trigger_ops *ops,
			    struct event_trigger_data *data,
			    struct trace_event_file *file)
{
	struct event_trigger_data *test;
	int ret = 0;

	list_for_each_entry_rcu(test, &file->triggers, list) {
		if (test->cmd_ops->trigger_type == data->cmd_ops->trigger_type) {
			ret = -EEXIST;
			goto out;
		}
	}

	if (data->ops->init) {
		ret = data->ops->init(data->ops, data);
		if (ret < 0)
			goto out;
	}

	list_add_rcu(&data->list, &file->triggers);
	ret++;

	update_cond_flag(file);
	if (trace_event_trigger_enable_disable(file, 1) < 0) {
		list_del_rcu(&data->list);
		update_cond_flag(file);
		ret--;
	}
out:
	return ret;
}

Where the comment is total wrong. It doesn't return 0 on success, it
returns 1. And if trace_event_trigger_enable_disable() fails it returns
zero.

And that can fail with the call->class->reg() return value, which could
fail for various strange reasons. I don't know why we would want to
return 0 when it fails?

I don't see where ->reg() would return anything but 1 on success. Maybe
I'm missing something. I'll look some more, but I'm thinking of changing
->reg() to return zero on all success, and negative on all errors and
just check those results.

-- Steve

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-13 16:27 [PATCH 0/3] tracing: Fix bugs on snapshot feature Masami Hiramatsu
2018-07-13 16:27 ` [PATCH 1/3] [BUGFIX] tracing: Fix double free of event_trigger_data Masami Hiramatsu
2018-07-24  2:10   ` Steven Rostedt
2018-07-24 15:09     ` Masami Hiramatsu
2018-07-24 20:49       ` Steven Rostedt
2018-07-24 21:30         ` Steven Rostedt [this message]
2018-07-24 23:13           ` Steven Rostedt
2018-07-25  1:16             ` Masami Hiramatsu
2018-07-25  2:41               ` Steven Rostedt
2018-07-25 14:14                 ` Masami Hiramatsu
2018-07-25 16:01           ` Tom Zanussi
2018-07-25 16:09             ` Steven Rostedt
2018-07-25  1:05         ` Masami Hiramatsu
2018-07-13 16:28 ` [PATCH 2/3] [BUGFIX] ring_buffer: tracing: Inherit the tracing setting to next ring buffer Masami Hiramatsu
2018-07-24  2:25   ` Steven Rostedt
2018-07-24 14:30     ` Masami Hiramatsu
2018-07-13 16:28 ` [PATCH 3/3] selftests/ftrace: Add snapshot and tracing_on test case Masami Hiramatsu

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