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Subject: Re: [PATCH] tracing/kprobes: Check whether get_kretprobe() returns
 NULL in kretprobe_dispatcher()
To:     "Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, Yonghong Song <yhs@fb.com>,
        bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <165366693881.797669.16926184644089588731.stgit@devnote2>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <0204f480-cdb0-e49f-9034-602eced02966@iogearbox.net>
Date:   Mon, 30 May 2022 21:33:23 +0200
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On 5/27/22 5:55 PM, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.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@fb.com>
> Fixes: d741bf41d7c7 ("kprobes: Remove kretprobe hash")
> Cc: stable@vger.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Steven, I presume you'll pick this fix up?

Thanks,
Daniel