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Subject: Re: [PATCH] kernel/kprobes: add check to avoid kprobe memory leak
To: Masami Hiramatsu <mhiramat@kernel.org>
CC: <ananth@linux.vnet.ibm.com>, <anil.s.keshavamurthy@intel.com>,
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References: <1508847422-63641-1-git-send-email-chenjiankang1@huawei.com>
 <20171026015453.ba08699319ffaa9a18bbd8e3@kernel.org>
From: chenjiankang <chenjiankang1@huawei.com>
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Date: Thu, 26 Oct 2017 09:22:23 +0800
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> On Tue, 24 Oct 2017 20:17:02 +0800
> JianKang Chen <chenjiankang1@huawei.com> wrote:
> 
>> The function register_kretprobe is used to initialize a struct
>> kretprobe and allocate a list table for kprobe instance.
>> However,in this function, there is a memory leak.
>>
>> The test case:
>>
>> static struct kretprobe rp;
>> struct  kretprobe *rps[10]={&rp ,&rp ,&rp ,
>> &rp ,&rp ,&rp ,&rp ,&rp ,&rp,&rp};
> 
> What ? this is buggy code. you must not list same kretprobe.
> But, year, since register_kprobe() already has similar protection against
> reusing, register_kretprobe() should do so.
> 
> [..]
>>  	raw_spin_lock_init(&rp->lock);
>> +
>> +	if (!hlist_empty(&rp->free_instances))
>> +		return -EBUSY;
>> +
> 
> Hmm, but can you use check_kprobe_rereg() before raw_spin_lock_init()?
> If user reuses rp after it starts, rp->lock can already be used.

Hmm, your advice is very good, we can use check_kprobe_rereg() at 
the beginning of the register_kretprobe();

For example:

int register_kretprobe(struct kretprobe *rp)
{
        int ret = 0;
        struct kretprobe_instance *inst;
        int i;
        void *addr;

        ret = check_kprobe_rereg(&rp->kp);
        if (ret)
                return ret;

Thank you!