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Date:   Fri, 28 Aug 2020 23:19:20 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     peterz@infradead.org
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Subject: Re: [RFC][PATCH 3/7] kprobes: Remove kretprobe hash
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On Fri, 28 Aug 2020 15:58:24 +0200
peterz@infradead.org wrote:

> On Fri, Aug 28, 2020 at 10:51:13PM +0900, Masami Hiramatsu wrote:
>  
> > OK, schedule function will be the key. I guess the senario is..
> > 
> > 1) kretporbe replace the return address with kretprobe_trampoline on task1's kernel stack
> > 2) the task1 forks task2 before returning to the kretprobe_trampoline
> > 3) while copying the process with the kernel stack, task2->kretprobe_instances.first = NULL
> > 4) task2 returns to the kretprobe_trampoline
> > 5) Bomb!
> > 
> > Hmm, we need to fixup the kernel stack when copying process. 
> 
> How would that scenario have been avoided in the old code? Because there
> task2 would have a different has and not have found a kretprobe_instance
> either.

Good question, I think this bug has not been solved in old code too.
Let me check.

Thanks,

-- 
Masami Hiramatsu <mhiramat@kernel.org>