linux-kernel - Re: [PATCH] tracing/kprobes: Check whether get_kretprobe() returns NULL in kretprobe

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Date:   Wed, 8 Jun 2022 14:38:39 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Steven Rostedt <rostedt@...dmis.org>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Yonghong Song <yhs@...com>,
        bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] tracing/kprobes: Check whether get_kretprobe() returns
 NULL in kretprobe_dispatcher()

On 5/31/22 12:00 AM, Steven Rostedt wrote:
> On May 30, 2022 9:33:23 PM GMT+02:00, Daniel Borkmann <daniel@...earbox.net> wrote:
>> On 5/27/22 5:55 PM, Masami Hiramatsu (Google) wrote:
>>> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>>>
>>> There is a small chance that get_kretprobe(ri) returns NULL in
>>> kretprobe_dispatcher() when another CPU unregisters the kretprobe
>>> right after __kretprobe_trampoline_handler().
>>>
>>> To avoid this issue, kretprobe_dispatcher() checks the get_kretprobe()
>>> return value again. And if it is NULL, it returns soon because that
>>> kretprobe is under unregistering process.
>>>
>>> This issue has been introduced when the kretprobe is decoupled
>>> from the struct kretprobe_instance by commit d741bf41d7c7
>>> ("kprobes: Remove kretprobe hash"). Before that commit, the
>>> struct kretprob_instance::rp directly points the kretprobe
>>> and it is never be NULL.
>>>
>>> Reported-by: Yonghong Song <yhs@...com>
>>> Fixes: d741bf41d7c7 ("kprobes: Remove kretprobe hash")
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>>
>> Steven, I presume you'll pick this fix up?
> 
> I'm currently at Embedded/Kernel Recipes, but yeah, I'll take a look at it. (Just need to finish my slides first ;-)

Ok, thanks. If I don't hear back I presume you'll pick it up then.