Re: [BUGFIX] kprobes: prevent re-registration of the same kprobe - take2

[Masami Hiramatsu <mhiramat@redhat.com>]

Ananth N Mavinakayanahalli wrote:
> On Mon, Sep 14, 2009 at 12:25:41PM -0400, Masami Hiramatsu wrote:
>> Ananth N Mavinakayanahalli wrote:
>>> On Sun, Sep 13, 2009 at 09:47:39PM -0400, Masami Hiramatsu wrote:
>>>> Ananth N Mavinakayanahalli wrote:
>>>>> On Fri, Sep 11, 2009 at 05:12:54AM +0200, Frederic Weisbecker wrote:
>>>>>> On Thu, Sep 10, 2009 at 07:53:30PM -0400, Masami Hiramatsu wrote:
> 
> ...
> 
>>> +static inline int check_kprobe_rereg(struct kprobe *p)
>>> +{
>>> +	int ret = 0;
>>> +	struct kprobe *old_p;
>>> +
>>> +	mutex_lock(&kprobe_mutex);
>>> +	old_p = __get_valid_kprobe(p);
>>> +	if (old_p == p)
>>
>> Here, since __get_valid_kprobe(p) will return aggr_kprobe of 'p',
>> you just need to check old_p != NULL.
> 
> Right!
> 
> ---
> Prevent re-registration of the same kprobe. This situation, though
> unlikely, needs to be flagged since it can lead to a system crash if its
> not handled.
> 
> The core change itself is small, but the helper routine needed to be
> moved around a bit; hence the diffstat.
> 
> Signed-off-by: Ananth N Mavinakayanahalli<ananth@in.ibm.com>

Acked-by: Masami Hiramatsu <mhiramat@redhat.com>

> ---
>  kernel/kprobes.c |   58 ++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 38 insertions(+), 20 deletions(-)
> 
> Index: linux-2.6.31/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.31.orig/kernel/kprobes.c
> +++ linux-2.6.31/kernel/kprobes.c
> @@ -681,6 +681,40 @@ static kprobe_opcode_t __kprobes *kprobe
>  	return (kprobe_opcode_t *)(((char *)addr) + p->offset);
>  }
>  
> +/* Check passed kprobe is valid and return kprobe in kprobe_table. */
> +static struct kprobe * __kprobes __get_valid_kprobe(struct kprobe *p)
> +{
> +	struct kprobe *old_p, *list_p;
> +
> +	old_p = get_kprobe(p->addr);
> +	if (unlikely(!old_p))
> +		return NULL;
> +
> +	if (p != old_p) {
> +		list_for_each_entry_rcu(list_p, &old_p->list, list)
> +			if (list_p == p)
> +			/* kprobe p is a valid probe */
> +				goto valid;
> +		return NULL;
> +	}
> +valid:
> +	return old_p;
> +}
> +
> +/* Return error if the kprobe is being re-registered */
> +static inline int check_kprobe_rereg(struct kprobe *p)
> +{
> +	int ret = 0;
> +	struct kprobe *old_p;
> +
> +	mutex_lock(&kprobe_mutex);
> +	old_p = __get_valid_kprobe(p);
> +	if (old_p)
> +		ret = -EINVAL;
> +	mutex_unlock(&kprobe_mutex);
> +	return ret;
> +}
> +
>  int __kprobes register_kprobe(struct kprobe *p)
>  {
>  	int ret = 0;
> @@ -693,6 +727,10 @@ int __kprobes register_kprobe(struct kpr
>  		return -EINVAL;
>  	p->addr = addr;
>  
> +	ret = check_kprobe_rereg(p);
> +	if (ret)
> +		return ret;
> +
>  	preempt_disable();
>  	if (!kernel_text_address((unsigned long) p->addr) ||
>  	    in_kprobes_functions((unsigned long) p->addr)) {
> @@ -762,26 +800,6 @@ out:
>  }
>  EXPORT_SYMBOL_GPL(register_kprobe);
>  
> -/* Check passed kprobe is valid and return kprobe in kprobe_table. */
> -static struct kprobe * __kprobes __get_valid_kprobe(struct kprobe *p)
> -{
> -	struct kprobe *old_p, *list_p;
> -
> -	old_p = get_kprobe(p->addr);
> -	if (unlikely(!old_p))
> -		return NULL;
> -
> -	if (p != old_p) {
> -		list_for_each_entry_rcu(list_p, &old_p->list, list)
> -			if (list_p == p)
> -			/* kprobe p is a valid probe */
> -				goto valid;
> -		return NULL;
> -	}
> -valid:
> -	return old_p;
> -}
> -
>  /*
>   * Unregister a kprobe without a scheduler synchronization.
>   */

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com