Re: [PATCH v2] kprobes: avoid the kprobe being re-registered

[Masami Hiramatsu]

On Fri, 27 Oct 2017 09:56:40 +0800
Zhou Chengming <zhouchengming1@xxxxxxxxxx> wrote:

> Changes from v1:
> - We should put the modifies of the kprobe after the re-reg check.
> - And then the address_safe check.
> - When check_kprobe_address_safe() return fail, the *probed_mod
>   should be set to NULL, and no module refcount held.

Could you split this item from this patch (with initializing probe_mod = NULL),
since it is another bug?

Thank you,

> 
> Old code use check_kprobe_rereg() to check if the kprobe has been
> registered already, but check_kprobe_rereg() will release the
> kprobe_mutex then, so maybe two paths will pass the check and
> register the same kprobe. This patch put the check inside the mutex.
> 
> Signed-off-by: Zhou Chengming <zhouchengming1@xxxxxxxxxx>
> ---
>  kernel/kprobes.c | 28 +++++++++-------------------
>  1 file changed, 9 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index a1606a4..f622639 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1443,19 +1443,6 @@ static struct kprobe *__get_valid_kprobe(struct kprobe *p)
>  	return ap;
>  }
>  
> -/* Return error if the kprobe is being re-registered */
> -static inline int check_kprobe_rereg(struct kprobe *p)
> -{
> -	int ret = 0;
> -
> -	mutex_lock(&kprobe_mutex);
> -	if (__get_valid_kprobe(p))
> -		ret = -EINVAL;
> -	mutex_unlock(&kprobe_mutex);
> -
> -	return ret;
> -}
> -
>  int __weak arch_check_ftrace_location(struct kprobe *p)
>  {
>  	unsigned long ftrace_addr;
> @@ -1501,6 +1488,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  		 * its code to prohibit unexpected unloading.
>  		 */
>  		if (unlikely(!try_module_get(*probed_mod))) {
> +			*probed_mod = NULL;
>  			ret = -ENOENT;
>  			goto out;
>  		}
> @@ -1536,9 +1524,13 @@ int register_kprobe(struct kprobe *p)
>  		return PTR_ERR(addr);
>  	p->addr = addr;
>  
> -	ret = check_kprobe_rereg(p);
> -	if (ret)
> -		return ret;
> +	mutex_lock(&kprobe_mutex);
> +
> +	/* Return error if the kprobe is being re-registered */
> +	if (__get_valid_kprobe(p)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
>  
>  	/* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
>  	p->flags &= KPROBE_FLAG_DISABLED;
> @@ -1547,9 +1539,7 @@ int register_kprobe(struct kprobe *p)
>  
>  	ret = check_kprobe_address_safe(p, &probed_mod);
>  	if (ret)
> -		return ret;
> -
> -	mutex_lock(&kprobe_mutex);
> +		goto out;
>  
>  	old_p = get_kprobe(p->addr);
>  	if (old_p) {
> -- 
> 1.8.3.1
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>