netdev - 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: <20191210132834.157d5fc5@cakuba.netronome.com>
Date:   Tue, 10 Dec 2019 13:28:34 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        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 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().