linux-kernel - Re: [PATCH 4.19 119/131] tracing: Fix event trigger to accept redundant spaces

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Date:   Thu, 2 Jul 2020 23:17:28 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 4.19 119/131] tracing: Fix event trigger to accept
 redundant spaces

Hi!

> commit 6784beada631800f2c5afd567e5628c843362cee upstream.
> 
> Fix the event trigger to accept redundant spaces in
> the trigger input.
> 
> For example, these return -EINVAL
> 
> echo " traceon" > events/ftrace/print/trigger
> echo "traceon  if common_pid == 0" > events/ftrace/print/trigger
> echo "disable_event:kmem:kmalloc " > events/ftrace/print/trigger
> 
> But these are hard to find what is wrong.
> 
> To fix this issue, use skip_spaces() to remove spaces
> in front of actual tokens, and set NULL if there is no
> token.

For the record, I'm not fan of this one. It is ABI change, not a
bugfix.

Yes, it makes kernel interface "easier to use". It also changes
interface in the middle of stable series, and if people start relying
on new interface and start putting extra spaces, they'll get nasty
surprise when they move code to the older kernel.

Best regards,
								Pavel

> +++ b/kernel/trace/trace_events_trigger.c
> @@ -211,11 +211,17 @@ static int event_trigger_regex_open(struct inode *inode, struct file *file)
>  
>  static int trigger_process_regex(struct trace_event_file *file, char *buff)
>  {
> -	char *command, *next = buff;
> +	char *command, *next;
>  	struct event_command *p;
>  	int ret = -EINVAL;
>  
> +	next = buff = skip_spaces(buff);
>  	command = strsep(&next, ": \t");
> +	if (next) {
> +		next = skip_spaces(next);
> +		if (!*next)
> +			next = NULL;
> +	}
>  	command = (command[0] != '!') ? command : command + 1;
>  
>  	mutex_lock(&trigger_cmd_mutex);
> @@ -624,8 +630,14 @@ event_trigger_callback(struct event_command *cmd_ops,
>  	int ret;
>  
>  	/* separate the trigger from the filter (t:n [if filter]) */
> -	if (param && isdigit(param[0]))
> +	if (param && isdigit(param[0])) {
>  		trigger = strsep(&param, " \t");
> +		if (param) {
> +			param = skip_spaces(param);
> +			if (!*param)
> +				param = NULL;
> +		}
> +	}
>  
>  	trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
>  
> @@ -1361,6 +1373,11 @@ int event_enable_trigger_func(struct event_command *cmd_ops,
>  	trigger = strsep(&param, " \t");
>  	if (!trigger)
>  		return -EINVAL;
> +	if (param) {
> +		param = skip_spaces(param);
> +		if (!*param)
> +			param = NULL;
> +	}
>  
>  	system = strsep(&trigger, ":");
>  	if (!trigger)

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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