linux-kernel - Re: [oss-drivers] [PATCH AUTOSEL 5.4 326/350] bpf: Switch bpf_map ref counter to atomic64_t so bpf_map

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Message-ID: <20191219232504.GV17708@sasha-vm>
Date:   Thu, 19 Dec 2019 18:25:04 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Andrii Nakryiko <andriin@...com>,
        Song Liu <songliubraving@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, oss-drivers@...ronome.com
Subject: Re: [oss-drivers] [PATCH AUTOSEL 5.4 326/350] bpf: Switch bpf_map
 ref counter to atomic64_t so bpf_map_inc() never fails

On Thu, Dec 12, 2019 at 05:25:13PM +0100, Daniel Borkmann wrote:
>On Tue, Dec 10, 2019 at 01:28:34PM -0800, Jakub Kicinski wrote:
>> On Tue, 10 Dec 2019 16:07:11 -0500, Sasha Levin wrote:
>> > From: Andrii Nakryiko <andriin@...com>
>> >
>> > [ Upstream commit 1e0bd5a091e5d9e0f1d5b0e6329b87bb1792f784 ]
>> >
>> > 92117d8443bc ("bpf: fix refcnt overflow") turned refcounting of bpf_map into
>> > potentially failing operation, when refcount reaches BPF_MAX_REFCNT limit
>> > (32k). Due to using 32-bit counter, it's possible in practice to overflow
>> > refcounter and make it wrap around to 0, causing erroneous map free, while
>> > there are still references to it, causing use-after-free problems.
>>
>> I don't think this is a bug fix, the second sentence here is written
>> in a quite confusing way, but there is no bug.
>>
>> Could you drop? I don't think it's worth the backporting pain since it
>> changes bpf_map_inc().
>
>Agree, this is not a bug fix and should not go to stable. (Also agree that
>the changelog is super confusing here and should have been done differently
>to avoid exactly where we are here. I think I pointed that out in the
>original patch, but seems this slipped through the cracks :/)

Sure, dropped, thanks!

-- 
Thanks,
Sasha