From: Richard Weinberger <richard@nod.at>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ast@kernel.org
Subject: Re: [PATCH 3/3] bpf: Make sure that ->comm does not change under us.
Date: Mon, 16 Oct 2017 23:10:37 +0200 [thread overview]
Message-ID: <2144178.MA8iAIlUE0@blindfold> (raw)
In-Reply-To: <59E51E4E.4060009@iogearbox.net>
Am Montag, 16. Oktober 2017, 23:02:06 CEST schrieb Daniel Borkmann:
> On 10/16/2017 10:55 PM, Richard Weinberger wrote:
> > Am Montag, 16. Oktober 2017, 22:50:43 CEST schrieb Daniel Borkmann:
> >>> struct task_struct *task = current;
> >>>
> >>> + task_lock(task);
> >>>
> >>> strncpy(buf, task->comm, size);
> >>>
> >>> + task_unlock(task);
> >>
> >> Wouldn't this potentially lead to a deadlock? E.g. you attach yourself
> >> to task_lock() / spin_lock() / etc, and then the BPF prog triggers the
> >> bpf_get_current_comm() taking the lock again ...
> >
> > Yes, but doesn't the same apply to the use case when I attach to strncpy()
> > and run bpf_get_current_comm()?
>
> You mean due to recursion? In that case trace_call_bpf() would bail out
> due to the bpf_prog_active counter.
Ah, that's true.
So, when someone wants to use bpf_get_current_comm() while tracing task_lock,
we have a problem. I agree.
On the other hand, without locking the function may return wrong results.
Thanks,
//richard
next prev parent reply other threads:[~2017-10-16 21:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-16 18:18 [PATCH 1/3] bpf: Don't check for current being NULL Richard Weinberger
2017-10-16 18:18 ` [PATCH 2/3] bpf: Remove dead variable Richard Weinberger
2017-10-16 18:54 ` Daniel Borkmann
2017-10-16 18:59 ` Richard Weinberger
2017-10-16 19:11 ` Daniel Borkmann
2017-10-16 19:22 ` Richard Weinberger
2017-10-16 20:48 ` Daniel Borkmann
2017-10-16 18:18 ` [PATCH 3/3] bpf: Make sure that ->comm does not change under us Richard Weinberger
2017-10-16 20:50 ` Daniel Borkmann
2017-10-16 20:55 ` Richard Weinberger
2017-10-16 21:02 ` Daniel Borkmann
2017-10-16 21:10 ` Richard Weinberger [this message]
-- strict thread matches above, loose matches on Subject: below --
2017-10-16 22:10 Alexei Starovoitov
2017-10-16 22:19 ` Daniel Borkmann
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