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

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Date:   Fri, 27 Oct 2017 14:16:59 +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 v2] kprobes: avoid the kprobe being re-registered

On 2017/10/27 13:57, Masami Hiramatsu wrote:
> On Fri, 27 Oct 2017 09:56:40 +0800
> Zhou Chengming<zhouchengming1@...wei.com>  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,

Ok, it seems more reasonable. I will split this patch into two patches later.

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@...wei.com>
>> ---
>>   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
>>
>