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Date:   Thu, 26 Oct 2017 15:21:30 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     chenjiankang <chenjiankang1@...wei.com>
Cc:     <ananth@...ux.vnet.ibm.com>, <anil.s.keshavamurthy@...el.com>,
        <linux-kernel@...r.kernel.org>, <xieyisheng1@...wei.com>,
        <wangkefeng.wang@...wei.com>, <davem@...emloft.net>
Subject: Re: [PATCH] kernel/kprobes: add check to avoid kprobe memory leak

On Thu, 26 Oct 2017 09:22:23 +0800
chenjiankang <chenjiankang1@...wei.com> wrote:

> > On Tue, 24 Oct 2017 20:17:02 +0800
> > JianKang Chen <chenjiankang1@...wei.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;

Yeah, this looks much better for me :)

Thanks,

> 
> Thank you!
>  
> 


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

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