linux-kernel - Re: [PATCH] kprobes: Fix kill kprobe which has been marked as gone

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Message-Id: <20200821212843.180dc6f2f417e60cff2b886c@kernel.org>
Date:   Fri, 21 Aug 2020 21:28:43 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     naveen.n.rao@...ux.ibm.com, anil.s.keshavamurthy@...el.com,
        davem@...emloft.net, songliubraving@...com,
        linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH] kprobes: Fix kill kprobe which has been marked as gone

Hi Muchun,

On Thu, 20 Aug 2020 11:19:33 +0800
Muchun Song <songmuchun@...edance.com> wrote:

> If a kprobe is marked as gone, we should not kill it again. Otherwise,
> we can disarm the kprobe more than once. In that case, the statistics
> of kprobe_ftrace_enabled can unbalance which can lead to that kprobe
> do not work.
> 

Good catch! Hmm, I think we also need an assertion in
kill_kprobe() so that p is already gone. Anyway, this looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks!

> Fixes: 0cb2f1372baa ("kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Co-developed-by: Chengming Zhou <zhouchengming@...edance.com>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  kernel/kprobes.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d36e2b017588..7bac3ea44ff4 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2422,7 +2422,10 @@ static int kprobes_module_callback(struct notifier_block *nb,
>  	mutex_lock(&kprobe_mutex);
>  	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
>  		head = &kprobe_table[i];
> -		hlist_for_each_entry(p, head, hlist)
> +		hlist_for_each_entry(p, head, hlist) {
> +			if (kprobe_gone(p))
> +				continue;
> +
>  			if (within_module_init((unsigned long)p->addr, mod) ||
>  			    (checkcore &&
>  			     within_module_core((unsigned long)p->addr, mod))) {
> @@ -2439,6 +2442,7 @@ static int kprobes_module_callback(struct notifier_block *nb,
>  				 */
>  				kill_kprobe(p);
>  			}
> +		}
>  	}
>  	if (val == MODULE_STATE_GOING)
>  		remove_module_kprobe_blacklist(mod);
> -- 
> 2.11.0
> 


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