linux-kernel - Re: [PATCH] tracepoints: prevents null probe from being added

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Message-ID: <1363800712.6345.17.camel@gandalf.local.home>
Date:	Wed, 20 Mar 2013 13:31:52 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	kpark3469@...il.com
Cc:	keun-o.park@...driver.com, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracepoints: prevents null probe from being added

On Wed, 2013-03-20 at 12:18 +0900, kpark3469@...il.com wrote:
> From: Sahara <keun-o.park@...driver.com>
> 
> Somehow tracepoint_entry_add/remove_probe functions allow a null probe
> function.

You actually hit this in practice, or is this just something that you
observe from code review?

>  Especially on getting a null probe in remove function, it seems
> to be used to remove all probe functions in the entry.

Hmm, that actually sounds like a feature.

> But, the code is not handled as expected. Since the tracepoint_entry
> maintains funcs array's last func as NULL in order to mark it as the end
> of the array. Also NULL func is used in for-loop to check out the end of
> the loop. So if there's NULL func in the entry's funcs, the for-loop
> will be abruptly ended in the middle of operation.
> Also checking out if probe is null in for-loop is not efficient.
> 
> Signed-off-by: Sahara <keun-o.park@...driver.com>
> ---
>  kernel/tracepoint.c |   18 ++++++++++++------
>  1 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 0c05a45..30f427e 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -112,7 +112,10 @@ tracepoint_entry_add_probe(struct tracepoint_entry *entry,
>  	int nr_probes = 0;
>  	struct tracepoint_func *old, *new;
>  
> -	WARN_ON(!probe);
> +	if (unlikely(!probe)) {
> +		WARN_ON(!probe);
> +		return ERR_PTR(-EINVAL);
> +	}

Um, you want:

	if (WARN_ON(!probe))
		return ERR_PTR(-EINVAL);

>  
>  	debug_print_probes(entry);
>  	old = entry->funcs;
> @@ -147,15 +150,19 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
>  
>  	old = entry->funcs;
>  
> +	if (unlikely(!probe)) {
> +		WARN_ON(!probe);
> +		return ERR_PTR(-EINVAL);
> +	}

Here too if it wasn't intended to allow removal of all probes from a
tracepoint.

> +
>  	if (!old)
>  		return ERR_PTR(-ENOENT);
>  
>  	debug_print_probes(entry);
>  	/* (N -> M), (N > 1, M >= 0) probes */
>  	for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> -		if (!probe ||
> -		    (old[nr_probes].func == probe &&
> -		     old[nr_probes].data == data))
> +		if (old[nr_probes].func == probe &&
> +		     old[nr_probes].data == data)
>  			nr_del++;
>  	}
>  
> @@ -173,8 +180,7 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
>  		if (new == NULL)
>  			return ERR_PTR(-ENOMEM);
>  		for (i = 0; old[i].func; i++)
> -			if (probe &&
> -			    (old[i].func != probe || old[i].data != data))
> +			if (old[i].func != probe || old[i].data != data)

This makes it look like the null probe was intentional.

-- Steve

>  				new[j++] = old[i];
>  		new[nr_probes - nr_del].func = NULL;
>  		entry->refcount = nr_probes - nr_del;


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