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Date:   Thu, 26 Oct 2017 23:39:44 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Zhou Chengming <zhouchengming1@...wei.com>
Cc:     <ananth@...ux.vnet.ibm.com>, <anil.s.keshavamurthy@...el.com>,
        <davem@...emloft.net>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kprobes: avoid the kprobe being re-registered

On Thu, 26 Oct 2017 20:11:25 +0800
Zhou Chengming <zhouchengming1@...wei.com> wrote:

> 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.

Still no good, see below comment.

> 
> Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com>
> ---
>  kernel/kprobes.c | 23 ++++++-----------------
>  1 file changed, 6 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index a1606a4..2a4873a 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;
> @@ -1536,10 +1523,6 @@ int register_kprobe(struct kprobe *p)
>  		return PTR_ERR(addr);
>  	p->addr = addr;
>  
> -	ret = check_kprobe_rereg(p);
> -	if (ret)
> -		return ret;
> -
>  	/* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
>  	p->flags &= KPROBE_FLAG_DISABLED;
>  	p->nmissed = 0;

here, we already modifies the kprobe. We need to check and reject before modifying it.

Thank you,

> @@ -1551,6 +1534,12 @@ int register_kprobe(struct kprobe *p)
>  
>  	mutex_lock(&kprobe_mutex);
>  
> +	/* Return error if the kprobe is being re-registered */
> +	if (__get_valid_kprobe(p)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
>  	old_p = get_kprobe(p->addr);
>  	if (old_p) {
>  		/* Since this may unoptimize old_p, locking text_mutex. */
> -- 
> 1.8.3.1
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>

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