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Date:   Fri, 27 Oct 2017 09:24:07 +0800
From:   zhouchengming <zhouchengming1@...wei.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
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 2017/10/26 22:39, Masami Hiramatsu wrote:
> 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,

Ah, right. We should put the modifies after the re-reg check. I will send a patch-v2.

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
>>
>


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