netdev - Re: [PATCH net] bpf: one perf event close won't free bpf program attached by another perf event

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Message-Id: <20170920.141248.405636883631460038.davem@davemloft.net>
Date:   Wed, 20 Sep 2017 14:12:48 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     yhs@...com
Cc:     peterz@...radead.org, rostedt@...dmis.org, ast@...com,
        daniel@...earbox.net, netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net] bpf: one perf event close won't free bpf program
 attached by another perf event

From: Yonghong Song <yhs@...com>
Date: Mon, 18 Sep 2017 16:38:36 -0700

> This patch fixes a bug exhibited by the following scenario:
>   1. fd1 = perf_event_open with attr.config = ID1
>   2. attach bpf program prog1 to fd1
>   3. fd2 = perf_event_open with attr.config = ID1
>      <this will be successful>
>   4. user program closes fd2 and prog1 is detached from the tracepoint.
>   5. user program with fd1 does not work properly as tracepoint
>      no output any more.
> 
> The issue happens at step 4. Multiple perf_event_open can be called
> successfully, but only one bpf prog pointer in the tp_event. In the
> current logic, any fd release for the same tp_event will free
> the tp_event->prog.
> 
> The fix is to free tp_event->prog only when the closing fd
> corresponds to the one which registered the program.
> 
> Signed-off-by: Yonghong Song <yhs@...com>

I've applied this and queued it up for -stable as it looks good
to me and 2 days is enough time for waiting for any other reviews.

Thanks.