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Date:   Mon, 28 Nov 2022 17:48:43 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Li Huafei <lihuafei1@huawei.com>
Cc:     <naveen.n.rao@linux.ibm.com>, <anil.s.keshavamurthy@intel.com>,
        <rostedt@goodmis.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kprobes: Fix check for probe enabled in kill_kprobe()
Message-Id: <20221128174843.244d5485156daf53b6406482@kernel.org>
In-Reply-To: <20221126114316.201857-1-lihuafei1@huawei.com>
References: <20221126114316.201857-1-lihuafei1@huawei.com>
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On Sat, 26 Nov 2022 19:43:16 +0800
Li Huafei <lihuafei1@huawei.com> wrote:

> In kill_kprobe(), the check whether disarm_kprobe_ftrace() needs to be
> called always fails. This is because before that we set the
> KPROBE_FLAG_GONE flag for kprobe so that "!kprobe_disabled(p)" is always
> false.

Good catch!

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thank you!

> 
> The disarm_kprobe_ftrace() call introduced by commit:
> 
>   0cb2f1372baa ("kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler")
> 
> to fix the NULL pointer reference problem. When the probe is enabled, if
> we do not disarm it, this problem still exists.
> 
> Fix it by putting the probe enabled check before setting the
> KPROBE_FLAG_GONE flag.
> 
> Fixes: 3031313eb3d54 ("kprobes: Fix to check probe enabled before disarm_kprobe_ftrace()")
> Signed-off-by: Li Huafei <lihuafei1@huawei.com>
> ---
>  kernel/kprobes.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 3050631e528d..a35074f0daa1 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2364,6 +2364,14 @@ static void kill_kprobe(struct kprobe *p)
>  
>  	lockdep_assert_held(&kprobe_mutex);
>  
> +	/*
> +	 * The module is going away. We should disarm the kprobe which
> +	 * is using ftrace, because ftrace framework is still available at
> +	 * 'MODULE_STATE_GOING' notification.
> +	 */
> +	if (kprobe_ftrace(p) && !kprobe_disabled(p) && !kprobes_all_disarmed)
> +		disarm_kprobe_ftrace(p);
> +
>  	p->flags |= KPROBE_FLAG_GONE;
>  	if (kprobe_aggrprobe(p)) {
>  		/*
> @@ -2380,14 +2388,6 @@ static void kill_kprobe(struct kprobe *p)
>  	 * the original probed function (which will be freed soon) any more.
>  	 */
>  	arch_remove_kprobe(p);
> -
> -	/*
> -	 * The module is going away. We should disarm the kprobe which
> -	 * is using ftrace, because ftrace framework is still available at
> -	 * 'MODULE_STATE_GOING' notification.
> -	 */
> -	if (kprobe_ftrace(p) && !kprobe_disabled(p) && !kprobes_all_disarmed)
> -		disarm_kprobe_ftrace(p);
>  }
>  
>  /* Disable one kprobe */
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>