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

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Date:   Tue, 31 May 2022 00:00:06 +0200
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Borkmann <daniel@...earbox.net>,
        "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 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 ;-)

-- Steve
>
>Thanks,
>Daniel

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